The Importance of Natural Selection
Zarrar Said April 2, 2008
#604 Posted by VRV on April 19, 2008 3:21:26 am
Long Post (C&P from
http://www.newscientist.com/channel/life/dn13620-evolution-24-myths-and-misc onceptions.html?DCMP=ILC-hmts&nsref=top1_head_Evolution:%2024%20myths%20and% 20misconceptions )
Cover page article in New Scientist. Very long post but very interesting.
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If you think you understand it, you don't know nearly enough about it
It will soon be 200 years since the birth of Charles Darwin and 150 years since the publication of On the Origin of Species, arguably the most important book ever written. In it, Darwin outlined an idea that many still find shocking – that all life on Earth, including human life, evolved through natural selection.
Darwin presented compelling evidence for evolution in On the Origin and, since his time, the case has become overwhelming. Countless fossil discoveries allow us to trace the evolution of today's organisms from earlier forms. DNA sequencing has confirmed beyond any doubt that all living creatures share a common origin. Innumerable examples of evolution in action can be seen all around us, from the pollution-matching pepper moth to fast-changing viruses such as HIV and H5N1 bird flu. Evolution is as firmly established a scientific fact as the roundness of the Earth.
And yet despite an ever-growing mountain of evidence, most people around the world are not taught the truth about evolution, if they are taught about it at all. Even in the UK, the birthplace of Darwin with an educated and increasingly secular population, one recent poll suggests less than half the population accepts evolution.
For those who have never had the opportunity to find out about biology or science, claims made by those who believe in supernatural alternatives to evolutionary theory can appear convincing. Meanwhile, even among those who accept evolution, misconceptions abound.
Most of us are happy to admit that we do not understand, say, the string theory in physics, yet we are all convinced we understand evolution. In fact, as biologists are discovering, its consequences can be stranger than we ever imagined. Evolution must be the best-known yet worst-understood of all scientific theories.
So here is New Scientist's guide to some of the most common myths and misconceptions about evolution.
Shared misconceptions:
Everything is an adaptation produced by natural selection
Natural selection is the only means of evolution
Natural selection leads to ever-greater complexity
Evolution produces creatures perfectly adapted to their environment
Evolution always promotes the survival of species
It doesn't matter if people do not understand evolution
"Survival of the fittest" justifies "everyone for themselves"
Evolution is limitlessly creative
Evolution cannot explain traits such as homosexuality
Creationism provides a coherent alternative to evolution
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We tend to assume that all characteristics of plants and animals are adaptations that have arisen through natural selection. Many are neither adaptations nor the result of selection at all.
Why do so many of us plonk ourselves down in front of the telly with a microwave meal after a tiring day? Because it's convenient? Or because TV meals are "the natural consequence of hundreds of thousands of years of human evolution"?
Stop laughing. You've probably made similar assumptions. For just about every aspect of our bodies and behaviour, it's easy to invent evolutionary "Just So" stories to explain how they came to be that way. We tend to assume that everything has a purpose, but often we are wrong.
Take male nipples. Male mammals clearly don't need them: they have them because females do and because it doesn't cost much to grow a nipple. So there has been no pressure for the sexes to evolve separate developmental pathways and "switch off" nipple growth in males. Some people claim the female orgasm exists for the same reason as male nipples, though this is a far more controversial idea.
Then there's our sense of smell. Do you find the scent of roses overwhelming or do you struggle to detect it? Can you detect the distinctive odour that most people's urine acquires after eating asparagus? People vary greatly when it comes to smell, largely due to chance mutations in the genes that code for the smell receptors rather than for adaptive reasons.
Yet other features are the result of selection, but not for the trait in question. For instance, the short stature of pygmies could be a side effect of selection for early childbearing in populations where mortality is high, rather than an adaptation in itself.
Multiskilled genes
Another reason why apparent adaptations can be side effects of selection for other traits is that genes can have different roles at different times of development or in different parts of the body. So selection for one variant can have all sorts of seemingly unrelated effects. Male homosexuality might be linked to gene variants that increase fertility in females, for instance.
A non-adaptive or detrimental gene variant can also spread rapidly through a population if it is on the same DNA strand as a highly beneficial variant. This is one reason why sex matters: when bits of DNA are swapped between chromosomes during sexual reproduction, good and bad variants can be split up.
Other features of plants and animals, such as the wings of ostriches, may once have been adaptations but are no longer needed for their original purpose. Such "vestigial traits" can persist because they are neutral, because they have taken on another function or because there hasn't been enough evolution to eliminate them even though they have become disadvantageous. Take the appendix. There are plenty of claims that it has this or that function but the evidence is clear: you are more likely to survive without an appendix than with one.
So why hasn't it disappeared? Because evolution is a numbers game. The worldwide human population was tiny until a few thousand years ago, and people have few children with long periods between each generation. That means fewer chances for evolution to throw up mutations that would reduce the size of the appendix or eliminate it altogether – and fewer chances for those mutations to spread through populations by natural selection. Another possibility is that we are stuck in an evolutionary Catch-22 where, as the appendix shrinks, appendicitis becomes more likely, favouring its retention.
Wisdom teeth are another vestigial remnant. A smaller, weaker jaw allowed our ancestors to grow larger brains, but left less room for molars. Yet many of us still grow teeth for which there is no room, with potentially fatal consequences. One possible reason why wisdom teeth persist is that they usually appear after people reach reproductive age, meaning selection against them is weak.
For all these reasons and more, we need to be sceptical of headline-grabbing claims about evolutionary explanations for different behaviours. Evolutionary psychology in particular is notorious for attempting to explain every aspect of behaviour, from gardening to rape, as an adaptation that arose when our ancestors lived on the African savannah.
Needless to say, without solid evidence, claims about how, for instance, TV dinners "evolved" should be taken with a large pinch of salt.
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Much change is due to random genetic drift rather than positive selection. It could be called the survival of the luckiest.
Take a look in the mirror. The face you see is rather different to that of a Neanderthal. Why? The unflattering answer could be for no other reason than random genetic drift. With features that can vary somewhat in form without greatly affecting function, such as the shape of the skull, chance might play a bigger role in their evolution than natural selection.
The DNA in all organisms is under constant attack from highly reactive chemicals and radiation, and errors are often made when it is copied. As a result, there are at least 100 new mutations in each human embryo, possibly far more. Some are harmful and are likely to be eliminated by natural selection – by death of the embryo, for instance. Most make no difference to our bodies, because most of our DNA is useless junk anyway. A few cause minor changes that are neither particularly harmful nor beneficial.
You might think that largely neutral mutations would remain restricted to a few individuals. In fact, while the vast majority of neutral mutations die out, a few spread throughout a population and thus become "fixed". It is pure chance – some just happen to be passed on to more and more individuals in each generation.
Although the likelihood of any neutral mutation spreading by chance is tiny, the enormous number of mutations in each generation makes genetic drift a significant force. It's a little like a lottery: the chance of winning is minuscule but because millions buy a ticket every week there is usually a winner.
As a result, most changes in the DNA of complex organisms over time are due to drift rather than selection, which is why biologists focus on sequences that are similar, or conserved, when they compare genomes. Natural selection will preserve sequences with vital functions, but the rest of the genome will change because of drift.
Drifting through bottlenecks
Genetic drift can even counteract natural selection. Many slightly beneficial mutations can be lost by chance, while mildly deleterious ones can spread and become fixed in a population. The smaller a population, the greater the role of genetic drift.
Population bottlenecks can have the same effect. Imagine an island where most mice are plain but a few have stripes. If a volcanic eruption wipes out all of the plain mice, the island will be repopulated by striped mice. It's a case of survival not of the fittest, but of the luckiest.
Random genetic drift has certainly played a big role in human evolution. Human populations were tiny until around 10,000 years ago, and went through a major bottleneck around 2 million years ago. Other bottlenecks occurred when a few individuals migrated out of Africa around 60,000 years ago and colonised other regions.
There is no doubt that most of the genetic differences between humans and other apes – and between different human populations – are due to genetic drift. However, most of these mutations are in the nine-tenths of our genome that is junk, so they make no difference. The interesting question is which mutations affecting our bodies or behaviour have spread because of drift rather than selection, but this is far from clear.
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In fact, natural selection often leads to ever greater simplicity. And, in many cases, complexity may initially arise when selection is weak or absent.
If you don't use it, you tend to lose it. Evolution often takes away rather than adding. For instance, cave fish lose their eyes, while parasites like tapeworms lose their guts.
Such simplification might be much more widespread than realised. Some apparently primitive creatures are turning out to be the descendants of more complex creatures rather than their ancestors. For instance, it appears the ancestor of brainless starfish and sea urchins had a brain.
Nevertheless, there is no doubt that evolution has produced more complex life-forms over the past four billion years. The tough question is: why? It is usually simply assumed to be the result of natural selection, but recently a few biologists studying our own bizarre and bloated genomes have challenged this idea.
Rather than being driven by selection, they propose that complexity initially arises when selection is weak or absent. How could this be? Suppose an animal has a gene that carries out two different functions. If mutation results in some offspring getting two copies of this gene, these offspring won't be any fitter as a result. In fact, they might be slightly less fit due to a double dose of the gene. In a large population where the selective pressure is strong, such mutations are likely to be eliminated. In smaller populations, where selective pressure is much weaker, these mutations could spread as a result of random genetic drift (see Natural selection is the only means of evolution) despite being slightly disadvantageous.
The more widely the duplicated genes spread in a population, the faster they will acquire mutations. A mutation in one copy might destroy its ability to carry out the first of the original gene's two functions. Then the other copy might lose the ability to perform the second of the two functions. As before, these mutations won't make the animals any fitter – such animals would still look and behave exactly the same – so they will not be selected for, but they could nevertheless spread by genetic drift.
Use your mutations
In this way, a species can go from having one gene with two functions to two genes that each carry out one function. This increase in complexity occurs not because of selection but despite it.
Once the genome is more complex, however, further mutations can make a creature’s body or behaviour more complex. For instance, having two separate genes means each can be switched on or off at different time or in different tissues. As soon as any beneficial mutations arise, natural selection will favour its spread.
If this picture is correct, it means that there are opposing forces at the heart of evolution. Complex structures and behaviour such as eyes and language are undoubtedly the product of natural selection. But when selection is strong – as in large populations – it blocks the random genomic changes that throw up this greater complexity in the first place.
This idea might even explain why evolution appears to speed up after environmental catastrophes such as asteroid impacts. Such events would slash the population size of species that survive, weakening selection and increasing the chances of greater genomic complexity arising through non-adaptive processes, paving the way for greater physical or behavioural complexity to arise through adaptive processes.
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You don't have to be perfectly adapted to survive, you just have to be as well adapted as your competitors. The apparent perfection of plants and animals may be more a reflection of our poor imaginations than of reality.
It's a theme repeated endlessly in wildlife documentaries. Again and again we are told how perfectly animals are adapted to their environment. It is, however, seldom true.
Take the UK's red squirrel. It appeared perfectly well adapted to its environment. Until the grey squirrel arrived, that is, and proved itself rather better adapted to broadleaf forests thanks, in part, to its ability to digest acorns.
There are many reasons why evolution does not produce "designs" that are as good as they could be. Natural selection's only criterion is that something works, not that it works as well as it might. Botched jobs are common, in fact. The classic example is the panda's thumb, which it uses to grasp bamboo. "The panda's true thumb is committed to another role. So the panda must... settle for an enlarged wrist bone and a somewhat clumsy, but quite workable, solution," wrote Stephen Jay Gould in 1978.
As this example shows, evolution is far more likely to reshape existing structures than to throw up novel ones. The lobed fins of early fish have turned into structures as diverse as wings, fins, hoofs and hands. We have five fingers because our amphibian ancestors had five digits, not because five is necessarily the optimal number of fingers for the human hand.
Many groups simply never evolve features that might have made them even more successful. Sharks lack the gas bladder that allows bony fish to control their buoyancy precisely, for example, and instead have to rely on swimming, buoyant fatty livers and, occasionally, a gulp of air. Similarly, mammals' two-way lungs are far less efficient than birds' one-way lungs. And sometimes creatures evolve features that actually reduce their overall fitness rather than increase it, such as the peacock's tail (see Evolution always increases fitness).
Use it or lose it
Continual mutation also means that if you don't use it, you lose it. For instance, many primates cannot make vitamin C, because of a gene mutation. This mutation makes no difference to animals that get plenty of vitamin C in their diet. However, when the environment changes, such loss of function can make a big difference, as one primate discovered on long sea voyages.
Evolution's lack of foresight can produce inherently flawed designs. The vertebrate eye – with its back-to-front wiring and blind spot where the wiring goes through the retina – is one example. Later adaptations have compensated for these problems to a large extent but once natural selection fixes upon a flawed, but workable, design, a species' descendants are usually stuck with it.
An organism's fitness is also relative to its environment, which is usually changing. There is a constant arms race going on between predator and prey, parasite and host. Many species have to evolve continuously just to maintain their current level of relative fitness, let alone get fitter. As the Red Queen says in Through the Looking Glass: "It takes all the running you can do, to keep in the same place."
Evolution's peak?
Humans are not running fast enough. Evolving through natural selection is about time and numbers. The number of new mutations that appear, and the number of chances that natural selection has to eliminate the harmful and favour the beneficial ones, depends on the size of a population, the number of offspring each individual has and on the number of generations, among other things.
We might like to think of ourselves as the most "highly evolved" species but, in terms of how many rounds of mutation and selection we've undergone, we are one of the least evolved species.
Around 10 billion new viral particles can be produced every day in the body of a person infected with HIV. By contrast, the total human population on Earth was no more than a few million until a few thousand years ago.
Furthermore, in a decade bacteria can produce 200,000 generations -- about the number of generations of humans there have been since our lineage split from that of chimpanzees. So it's hardly surprising that in less than a human lifespan we’ve seen the evolution of new diseases such as HIV and numerous antibiotic-resistant bacteria.
Although human evolution has sped up in the past 10,000 years, we are changing our environment faster still. As a result, instead of becoming better adapted we are actually becoming less well adapted to the world we are creating. Think of the huge range of modern afflictions, from obesity and allergies to short-sightedness and drug addiction, we suffer from. Viruses and bacteria might approach perfection, but we humans are at best a very rough first draft.
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The phrase "survival of fittest" is widely misunderstood (see 'Survival of the fittest' justifies everyone for themselves). Many wrongly assume it means that evolution always increases the chances of a species surviving.
Evolution sometimes results in individuals or populations becoming less fit and may occasionally even lead to extinction.
There are several ways in which evolution can reduce the overall fitness of individuals or of populations. For starters, natural selection can take place at different levels – genes, individuals, groups – and what promotes the survival of a gene does not necessarily increase the fitness of the individuals carrying it, or of groups of these individuals.
For example, parasitic DNA elements, or transposons, can spread through a population even though they make their host organisms less fit. Transposons are one cause of genetic diseases such as haemophilia.
Similarly, selfish individuals may thrive at the expense of altruistic individuals in a group – making them the "fittest" – even though they make the group as a whole less competitive. Such cheaters can have disastrous consequences.
In 1932, J. B. S. Haldane suggested this could even lead to the extinction of populations – a phenomenon called evolutionary suicide. Models and some experimental evidence suggest he was right.
For instance, when nutrients run low, individual myxobacteria (slime bacteria) may come together to form a fruiting body to produce spores. Lab studies have shown that cheating myxobacteria that only produce spores and never help form the non-spore producing parts of the fruiting body can drive populations to extinction.
Genes capable of driving populations to extinction might have a practical use, however. Biologists are exploring the possibility of releasing engineered parasitic DNA into populations of malaria-carrying mosquitoes.
There is concern that something similar could happen accidentally. Fish that have been genetically modified to produce a growth hormone grow faster and larger, mature earlier and produce more eggs. But they are less likely to survive in the wild than unmodified fish. According to the Trojan gene hypothesis, a gene variant that produces such characteristics could spread rapidly through a wild population despite reducing individual fitness, and eventually drive the population to extinction.
Another way in which evolution can reduce a species' chances of survival is through the accumulation of detrimental mutations. Mutations provide the vital raw material for natural selection, so if the mutation rate is too low a population will not be able to evolve fast enough to keep up with environmental changes.
If, on the other hand, a population's mutation rate is too high, detrimental mutations may accumulate faster than natural selection can eliminate them. Eventually, the number of mutations can exceed the "error catastrophe threshold", again leading to the extinction of a population.
In theory, any species with a very small population could accumulate deleterious mutations faster than it can eliminate them. The problem is especially severe for asexual organisms such as the Amazon molly – an effect known as Muller's rachet.
It is far less of a problem for sexually reproducing species because the exchange of genetic material between chromosomes can separate good and bad mutations. Some unlucky offspring get saddled with lots of nasty mutations and die out, while the lucky ones get hardly any.
In theory, a mutation catastrophe can also occur as a result of linkage. This refers to gene variants that are inherited together because they sit next to each other on a chromosome. Suppose a mutation that greatly increases the mutation rate somehow ends up next to a new mutation that greatly increases fitness. The immediate fitness benefits of the beneficial mutation will initially mask the deleterious effects of the "mutator" mutation, meaning both mutations will rapidly sweep through a population, ultimately with disastrous consequences.
A few doctors hope to exploit mutation accumulation to treat diseases. Certain viruses such as HIV are already close to the error catastrophe threshold. Drugs that increase the mutation rate of the viruses still further might push them over the threshold and drive a population of viruses inside a person's body to extinction.
Finallly, it has long been recognised that the competition between members of the same species to reproduce – sexual selection – can favour traits that reduce a species' overall fitness. Male peacocks with the biggest and brightest tails might get the females' attention, but lugging around a heavy, conspicuous tail reduces their chances of survival.
Studies of threatened bird species suggest that sexual selection can indeed drive populations to extinction. Some biologists go so far as to blame sexual selection for the conspicuous consumption that threatens humanity's future.
According to the handicap principle, features such as peacocks' tails evolve precisely because they are disadvantageous. Consider an individual who is trying to signal to females how fit and strong he is. If the signal is easy to make, weaker males can easily cheat by making the same signal. But if making the signal is costly – such as growing a large, clumsy tail or giving away food – there's no way to cheat.
Proving that any of these phenomena have ever led to extinctions in the wild is far from easy, because any species to which this has happened are, of course, no longer around to study. The indirect evidence is growing ever stronger, though.
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At an individual level, it might not matter much. However, any modern society which bases major decisions on superstition rather than reality is heading for disaster
So your brother or mother is a creationist. Let them believe what they want, you might think. After all, it makes family get-togethers a lot easier and no difference to anyone else.
Or does it? Imagine if Mike Huckabee ends up as vice-president of the US – a mere heart attack away from the top job. Would you feel comfortable if the world's biggest superpower was run by a man who rejects evolution, thanks to the support of tens of millions of people who also refuse to accept the truth?
It is dangerous when leaders prefer dogma to biological reality: Stalin's support for the pseudoscience of Lysenko was a disaster for Soviet agriculture.
Evolving problems
The success of western civilisation is based on science and technology, on understanding and manipulating the world. Its continued success depends on this, perhaps now more than ever.
Any leader who thinks evolution is a matter of belief is arguably unfit for office. How can someone who dismisses the staggering amount of evidence for evolution assembled by researchers in myriad fields possibly evaluate more subtle scientific evidence for, say, climate change?
What's more, evolution is directly relevant to many policy decisions. Infectious diseases from tuberculosis to wheat rust are making a comeback as they evolve resistance to our defences. Antibiotic-resistant superbugs like MRSA are a growing problem. A deadly virus such as H5N1 bird flu or ebola might evolve the ability to spread from human to human at any time, leading to a devastating pandemic. It is not possible to grasp how serious these threats are and plan for them unless you understand the power of evolution.
There are many more subtle areas where understanding evolution matters too. For instance, fishing policies that allow fishermen to keep only large fish are actually leading to the evolution of smaller fish. The tremendous changes we are making to the environment are altering many species, from rats becoming resistant to poisons to urban birds changing their songs to counter noise pollution.
There is our future, too. Modern biology is on the brink of giving us previously unimaginable power over the human body, from reshaping embryos to rewriting the genetic code and delaying the effects of ageing. Societies' views on if and how these powers should be used will inevitably be shaped by people's understanding of their evolutionary origins. Things look rather different depending whether you think we are a perfect, finished product or crude early prototypes thrown up by a desperately cruel process from whose clutches we now have to break free.
This is not to say that evolutionary theory tells us how to run societies (see Survival of the fittest justifies everyone for themselves) or make ethical decisions (see Accepting evolution undermines morality). It doesn't. It is a descriptive science, not a prescriptive one. It does, however, help us to make informed decisions.
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The "fittest" can be the most loving and selfless, not the most aggressive and violent. In any case, what happens in nature does not justify people behaving in the same way
The phrase "survival of the fittest", which was coined not by Darwin but by the philosopher Herbert Spencer, is widely misunderstood.
For starters, there is a lot more to evolution by natural selection than just the survival of the fittest. There must also be a population of replicating entities and variations between them that affect fitness – variation that must be heritable. By itself, survival of the fittest is a dead end. Business people are especially guilty of confusing survival of the fittest with evolution.
What's more, although the phrase conjures up an image of a violent struggle for survival, in reality the word "fittest" seldom means the strongest or the most aggressive. On the contrary, it can mean anything from the best camouflaged or the most fecund to the cleverest or the most cooperative. Forget Rambo, think Einstein or Gandhi.
What we see in the wild is not every animal for itself. Cooperation is an incredibly successful survival strategy. Indeed it has been the basis of all the most dramatic steps in the history of life. Complex cells evolved from cooperating simple cells. Multicellular organisms are made up of cooperating complex cells. Superorganisms such as bee or ant colonies consist of cooperating individuals.
Suicidal cells
When cooperation breaks down, the results can be disastrous. When cells in our bodies turn rogue, for instance, the result is cancer. So elaborate mechanisms have evolved to maintain cooperation and suppress selfishness, such as cellular "surveillance" programmes that trigger cell suicide if they start to turn cancerous.
Looked at from this point of view, the concept of the survival of the fittest could be used to justify socialism rather than laissez-faire capitalism. Then again, the success of social insects could be used to argue for totalitarianism. Which illustrates another point: it is nonsense to appeal to the "survival of the fittest" to justify any economic or political ideology, especially on the basis that it is "natural".
Is cannibalism fine because polar bears do it? Is killing your brother or sister fine because nestlings of many bird species do it? Is murdering your children fine because mice sometimes eat their own pups? Is paedophilia fine because bonobo adults have sex with juveniles?
Powerful grip
Just about every kind of behaviour that most of us regard as "unnatural" turns out to be perfectly natural in some nook or cranny of the animal kingdom. No one can plausibly argue that this justifies humans behaving in the same way.
Yet even though such examples expose the utter absurdity of appealing to what is "natural" to judge right from wrong – the naturalistic fallacy – we seem to have a strange blind spot when it comes to evolution. Survival of the fittest has been claimed to justify all kinds of things, from free markets to eugenics. Such notions still have a powerful grip in some circles.
However, natural selection is simply a description of what happens in the living world. It does not tell us how we should behave.
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It might seem like there is no end to nature's inventiveness but there are some features that could probably never evolve, at least on Earth
It often seems that nature invented pretty much everything that can be invented long before humans arrived on the scene – including the wheel, kind of. There is a salamander living in the Californian mountains that coils itself up and rolls downhill when threatened, for example. The pearl moth caterpillar goes one better and can roll itself along a flat surface for four or five revolutions to escape predators.
Nevertheless, there are structures that would clearly be useful but have never evolved. Zebras with built-in machine guns would rarely be bothered by lions, some point out. So why can evolution invent some things but not others?
This is an extremely difficult issue to tackle: how can we study something that has not happened? One way to approach it is to start with a question used by those who deny evolution and believe that many of nature's inventions, such as the eye or the bacterial flagellum, are simply too complex to have evolved. What use is half a wing, they ask? (see Half a wing is no use)
Very useful, it turns out. The wings of insects might have evolved from flapping gills that were originally used for rowing on the surface of water. This is an example of exaptation – structures and behaviours that evolved for one purpose but take on a wholly new one, while remaining useful at every intermediate stage.
Come in, over
Turn this argument around, however, and it suggests that some features cannot evolve because a half-way stage really would be of no use. For example, two-way radio might be useful for many different animals, for making silent alarm calls or locating other members of your species. So why hasn't it evolved? The recent invention of nanoscale radio receivers suggests it is not physically impossible.
The answer might be that half a radio really is useless. Detecting natural radio waves – from lightning, for instance – would not tell animals anything useful about their environment. That means there will be no selection for mutations that allow organisms to detect radio waves. Conversely, without any means of detecting radio waves, emitting them would serve no useful purpose. Radar might not be able to evolve for similar reasons.
The contrast with visible light could hardly be greater. It is clear that simply detecting the presence or absence of light would be advantageous in many environments, that even a blurry picture is better than nothing at all, and so on right up to hawk-eyed sharpness.
Seaweed skies
Emitting visible light can be helpful too, even for creatures that cannot detect it themselves. For the bioluminescent phytoplankton that light up ocean waves, for instance, it is a way of summoning predators that eat the phytoplankton's enemies. A similar argument applies to sound: it is not hard to see how forms of echolocation evolved independently in groups such as bats, cave swiftlets and whales.
One might also wonder why plants that float in the sky like balloons have never evolved. The idea does not seem too far-fetched at first glance: many seaweeds have floats called pneumatocysts, filled with oxygen or carbon dioxide. Other algae can produce hydrogen. So fill a large, thin pneumatocyst with hydrogen and perhaps a seaweed could fly. Flying plants would beat water and land plants to the light, giving them a big advantage, so why aren't our skies filled with living green balloons?
Perhaps partly because large pneumatocysts with extremely thin membranes would be far more vulnerable to predators and damage from waves, so an intermediate stage could never evolve. What's more, algae produce hydrogen only when there's a lack of sulphur in the water, and in any case the molecules of hydrogen gas are so tiny that they would leak out of any pneumatocyst. Half a hydrogen balloon doesn't look very good for anything, at least on our planet. Even evolution has its limits.
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There are numerous evolutionary mechanisms that might explain homosexual behaviour, which is common in many species of animals
"Simple reasoning shows that evolution cannot explain homosexuality – how would a homosexuality gene get selected for?" "Why have the genetic traits predisposing to homosexuality not been eliminated long ago?"
Such arguments are surprisingly common – and completely wrong.
Homosexual behaviour has been observed in hundreds of species, from bison to penguins. It is still not clear to what extent homosexuality in humans or other animals is genetic (rather than, say, due to hormonal extremes during embryonic development), but there are many mechanisms that could explain why gene variants linked to homosexuality are maintained in a population.
A common assumption is that homosexuality means not having children, but this is not necessarily true, especially in cultures other than our own. Until it became acceptable for same-sex couples to live together in western countries, many homosexual people had partners of the opposite sex. In some traditional societies, various forms of non-exclusive homosexuality were common.
Reasons why
Among animals, homosexual behaviour is usually non-exclusive. For instance, in some populations of Japanese macaques, females prefer female sexual partners to male ones but still mate with males – they are bisexual, in other words.
It has also been suggested that homosexuality boosts individuals' reproductive success, albeit indirectly. For instance, same-sex partners might have a better chance of rising to the top of social hierarchies and getting access to the opposite sex. In some gull species, homosexual partnerships might be a response to a shortage of males – rather than have no offspring at all, some female pairs raise offspring together after mating with a male from a normal male-female pair.
Another possibility is that homosexuality evolves and persists because it benefits groups or relatives, rather than individuals. In bonobos, homosexual behaviour might have benefits at a group level by promoting social cohesion. One study in Samoa found gay men devote more time to their nieces and nephews, suggesting it might be an example of kin selection (promoting your own genes in the bodies of others).
For your health
Or perhaps homosexuality is neutral, neither reducing nor boosting overall fitness. Attempts to find an adaptive explanation for homosexual behaviour in macaques have failed, leading to suggestions that they do it purely for pleasure.
Even if homosexuality does reduce reproductive success, as most people assume, there are plenty of possible reasons why it is so common. For instance, gene variants that cause homosexual behaviour might have other, beneficial effects such as boosting fertility in women, as one recent study suggests, just as the gene variant for sickle-cell anaemia is maintained because it reduces the severity of malaria. Homosexuality could also be a result of females preferring males with certain tendencies – sexual selection can favour traits that reduce overall fitness, such as the peacock's tail (see Evolution always increases fitness).
Given that, until recently, homosexual behaviour in animals was ignored or even denied, it's hardly surprising that we cannot yet say for sure which of these explanations is correct. It could well turn out that different explanations are true in different species.
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The only thing that creationists agree on is that they don't like evolution. Even Genesis gives two contradictory accounts of creation
If someone tells you that creationism provides a better explanation for life on Earth than the theory of evolution, ask them which version of creationism.
Among creationists, there is an extraordinary range of beliefs about how life came to be. A few creationists accept that evolution produced the great diversity of life on Earth – apart from humans. Others think all life evolved but that the process was guided by a supernatural being.
Other creationists accept that evolution can lead to minor changes (microevolution) but deny that lots of little changes can result in new species or even new groups of organisms (macroevolution). Some think a deity created the very first life but then left it to evolve by itself.
Then there's the vexed issue of timing. "Young Earth Creationists" regard the Genesis account as "inerrant" despite its contradictions (see Evolution is wrong because the Bible is inerrant), and claim the planet was created about 6000 years ago. "Old Earth Creationists" meanwhile accept the hundreds of lines of evidence suggesting otherwise.
God, amok
This schism is just the beginning. Some don't dispute the earth's apparent age but believe it is an illusion (the omphalos hypothesis, which some summarise as "God faked it"). Yet others claim that the planet itself is billions of years old but that life on it was created only recently.
Creationists do at least all believe in a creator. But who is it: God, Allah, Yahweh, Brahma, Zeus, Olorun, aliens or a giant hermaphrodite?
Those who have studied our planet and the life on it, however, have come to very clear conclusions: the Earth is around 4 billion years old and all the life on it gradually evolved from much simpler forms. There is no evidence of any kind of outside intervention, and no need to invoke it to explain what is known. Yes, there are many debates among biologists, geologists and cosmologists over the finer details, but these will be resolved sooner or later by new discoveries or experiments. Reality is the ultimate arbiter.
By contrast, there is no way to resolve the often vast differences between the numerous forms of creationism. Anyone can come up with their own version of creationism (and many do). How do you convince the followers of the Flying Spaghetti Monster, for instance, that his noodle is not the real creator?
http://www.newscientist.com/channel/life/dn13620-evolution-24-myths-and-misc onceptions.html?DCMP=ILC-hmts&nsref=top1_head_Evolution:%2024%20myths%20and% 20misconceptions )
Cover page article in New Scientist. Very long post but very interesting.
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If you think you understand it, you don't know nearly enough about it
It will soon be 200 years since the birth of Charles Darwin and 150 years since the publication of On the Origin of Species, arguably the most important book ever written. In it, Darwin outlined an idea that many still find shocking – that all life on Earth, including human life, evolved through natural selection.
Darwin presented compelling evidence for evolution in On the Origin and, since his time, the case has become overwhelming. Countless fossil discoveries allow us to trace the evolution of today's organisms from earlier forms. DNA sequencing has confirmed beyond any doubt that all living creatures share a common origin. Innumerable examples of evolution in action can be seen all around us, from the pollution-matching pepper moth to fast-changing viruses such as HIV and H5N1 bird flu. Evolution is as firmly established a scientific fact as the roundness of the Earth.
And yet despite an ever-growing mountain of evidence, most people around the world are not taught the truth about evolution, if they are taught about it at all. Even in the UK, the birthplace of Darwin with an educated and increasingly secular population, one recent poll suggests less than half the population accepts evolution.
For those who have never had the opportunity to find out about biology or science, claims made by those who believe in supernatural alternatives to evolutionary theory can appear convincing. Meanwhile, even among those who accept evolution, misconceptions abound.
Most of us are happy to admit that we do not understand, say, the string theory in physics, yet we are all convinced we understand evolution. In fact, as biologists are discovering, its consequences can be stranger than we ever imagined. Evolution must be the best-known yet worst-understood of all scientific theories.
So here is New Scientist's guide to some of the most common myths and misconceptions about evolution.
Shared misconceptions:
Everything is an adaptation produced by natural selection
Natural selection is the only means of evolution
Natural selection leads to ever-greater complexity
Evolution produces creatures perfectly adapted to their environment
Evolution always promotes the survival of species
It doesn't matter if people do not understand evolution
"Survival of the fittest" justifies "everyone for themselves"
Evolution is limitlessly creative
Evolution cannot explain traits such as homosexuality
Creationism provides a coherent alternative to evolution
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We tend to assume that all characteristics of plants and animals are adaptations that have arisen through natural selection. Many are neither adaptations nor the result of selection at all.
Why do so many of us plonk ourselves down in front of the telly with a microwave meal after a tiring day? Because it's convenient? Or because TV meals are "the natural consequence of hundreds of thousands of years of human evolution"?
Stop laughing. You've probably made similar assumptions. For just about every aspect of our bodies and behaviour, it's easy to invent evolutionary "Just So" stories to explain how they came to be that way. We tend to assume that everything has a purpose, but often we are wrong.
Take male nipples. Male mammals clearly don't need them: they have them because females do and because it doesn't cost much to grow a nipple. So there has been no pressure for the sexes to evolve separate developmental pathways and "switch off" nipple growth in males. Some people claim the female orgasm exists for the same reason as male nipples, though this is a far more controversial idea.
Then there's our sense of smell. Do you find the scent of roses overwhelming or do you struggle to detect it? Can you detect the distinctive odour that most people's urine acquires after eating asparagus? People vary greatly when it comes to smell, largely due to chance mutations in the genes that code for the smell receptors rather than for adaptive reasons.
Yet other features are the result of selection, but not for the trait in question. For instance, the short stature of pygmies could be a side effect of selection for early childbearing in populations where mortality is high, rather than an adaptation in itself.
Multiskilled genes
Another reason why apparent adaptations can be side effects of selection for other traits is that genes can have different roles at different times of development or in different parts of the body. So selection for one variant can have all sorts of seemingly unrelated effects. Male homosexuality might be linked to gene variants that increase fertility in females, for instance.
A non-adaptive or detrimental gene variant can also spread rapidly through a population if it is on the same DNA strand as a highly beneficial variant. This is one reason why sex matters: when bits of DNA are swapped between chromosomes during sexual reproduction, good and bad variants can be split up.
Other features of plants and animals, such as the wings of ostriches, may once have been adaptations but are no longer needed for their original purpose. Such "vestigial traits" can persist because they are neutral, because they have taken on another function or because there hasn't been enough evolution to eliminate them even though they have become disadvantageous. Take the appendix. There are plenty of claims that it has this or that function but the evidence is clear: you are more likely to survive without an appendix than with one.
So why hasn't it disappeared? Because evolution is a numbers game. The worldwide human population was tiny until a few thousand years ago, and people have few children with long periods between each generation. That means fewer chances for evolution to throw up mutations that would reduce the size of the appendix or eliminate it altogether – and fewer chances for those mutations to spread through populations by natural selection. Another possibility is that we are stuck in an evolutionary Catch-22 where, as the appendix shrinks, appendicitis becomes more likely, favouring its retention.
Wisdom teeth are another vestigial remnant. A smaller, weaker jaw allowed our ancestors to grow larger brains, but left less room for molars. Yet many of us still grow teeth for which there is no room, with potentially fatal consequences. One possible reason why wisdom teeth persist is that they usually appear after people reach reproductive age, meaning selection against them is weak.
For all these reasons and more, we need to be sceptical of headline-grabbing claims about evolutionary explanations for different behaviours. Evolutionary psychology in particular is notorious for attempting to explain every aspect of behaviour, from gardening to rape, as an adaptation that arose when our ancestors lived on the African savannah.
Needless to say, without solid evidence, claims about how, for instance, TV dinners "evolved" should be taken with a large pinch of salt.
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Much change is due to random genetic drift rather than positive selection. It could be called the survival of the luckiest.
Take a look in the mirror. The face you see is rather different to that of a Neanderthal. Why? The unflattering answer could be for no other reason than random genetic drift. With features that can vary somewhat in form without greatly affecting function, such as the shape of the skull, chance might play a bigger role in their evolution than natural selection.
The DNA in all organisms is under constant attack from highly reactive chemicals and radiation, and errors are often made when it is copied. As a result, there are at least 100 new mutations in each human embryo, possibly far more. Some are harmful and are likely to be eliminated by natural selection – by death of the embryo, for instance. Most make no difference to our bodies, because most of our DNA is useless junk anyway. A few cause minor changes that are neither particularly harmful nor beneficial.
You might think that largely neutral mutations would remain restricted to a few individuals. In fact, while the vast majority of neutral mutations die out, a few spread throughout a population and thus become "fixed". It is pure chance – some just happen to be passed on to more and more individuals in each generation.
Although the likelihood of any neutral mutation spreading by chance is tiny, the enormous number of mutations in each generation makes genetic drift a significant force. It's a little like a lottery: the chance of winning is minuscule but because millions buy a ticket every week there is usually a winner.
As a result, most changes in the DNA of complex organisms over time are due to drift rather than selection, which is why biologists focus on sequences that are similar, or conserved, when they compare genomes. Natural selection will preserve sequences with vital functions, but the rest of the genome will change because of drift.
Drifting through bottlenecks
Genetic drift can even counteract natural selection. Many slightly beneficial mutations can be lost by chance, while mildly deleterious ones can spread and become fixed in a population. The smaller a population, the greater the role of genetic drift.
Population bottlenecks can have the same effect. Imagine an island where most mice are plain but a few have stripes. If a volcanic eruption wipes out all of the plain mice, the island will be repopulated by striped mice. It's a case of survival not of the fittest, but of the luckiest.
Random genetic drift has certainly played a big role in human evolution. Human populations were tiny until around 10,000 years ago, and went through a major bottleneck around 2 million years ago. Other bottlenecks occurred when a few individuals migrated out of Africa around 60,000 years ago and colonised other regions.
There is no doubt that most of the genetic differences between humans and other apes – and between different human populations – are due to genetic drift. However, most of these mutations are in the nine-tenths of our genome that is junk, so they make no difference. The interesting question is which mutations affecting our bodies or behaviour have spread because of drift rather than selection, but this is far from clear.
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In fact, natural selection often leads to ever greater simplicity. And, in many cases, complexity may initially arise when selection is weak or absent.
If you don't use it, you tend to lose it. Evolution often takes away rather than adding. For instance, cave fish lose their eyes, while parasites like tapeworms lose their guts.
Such simplification might be much more widespread than realised. Some apparently primitive creatures are turning out to be the descendants of more complex creatures rather than their ancestors. For instance, it appears the ancestor of brainless starfish and sea urchins had a brain.
Nevertheless, there is no doubt that evolution has produced more complex life-forms over the past four billion years. The tough question is: why? It is usually simply assumed to be the result of natural selection, but recently a few biologists studying our own bizarre and bloated genomes have challenged this idea.
Rather than being driven by selection, they propose that complexity initially arises when selection is weak or absent. How could this be? Suppose an animal has a gene that carries out two different functions. If mutation results in some offspring getting two copies of this gene, these offspring won't be any fitter as a result. In fact, they might be slightly less fit due to a double dose of the gene. In a large population where the selective pressure is strong, such mutations are likely to be eliminated. In smaller populations, where selective pressure is much weaker, these mutations could spread as a result of random genetic drift (see Natural selection is the only means of evolution) despite being slightly disadvantageous.
The more widely the duplicated genes spread in a population, the faster they will acquire mutations. A mutation in one copy might destroy its ability to carry out the first of the original gene's two functions. Then the other copy might lose the ability to perform the second of the two functions. As before, these mutations won't make the animals any fitter – such animals would still look and behave exactly the same – so they will not be selected for, but they could nevertheless spread by genetic drift.
Use your mutations
In this way, a species can go from having one gene with two functions to two genes that each carry out one function. This increase in complexity occurs not because of selection but despite it.
Once the genome is more complex, however, further mutations can make a creature’s body or behaviour more complex. For instance, having two separate genes means each can be switched on or off at different time or in different tissues. As soon as any beneficial mutations arise, natural selection will favour its spread.
If this picture is correct, it means that there are opposing forces at the heart of evolution. Complex structures and behaviour such as eyes and language are undoubtedly the product of natural selection. But when selection is strong – as in large populations – it blocks the random genomic changes that throw up this greater complexity in the first place.
This idea might even explain why evolution appears to speed up after environmental catastrophes such as asteroid impacts. Such events would slash the population size of species that survive, weakening selection and increasing the chances of greater genomic complexity arising through non-adaptive processes, paving the way for greater physical or behavioural complexity to arise through adaptive processes.
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You don't have to be perfectly adapted to survive, you just have to be as well adapted as your competitors. The apparent perfection of plants and animals may be more a reflection of our poor imaginations than of reality.
It's a theme repeated endlessly in wildlife documentaries. Again and again we are told how perfectly animals are adapted to their environment. It is, however, seldom true.
Take the UK's red squirrel. It appeared perfectly well adapted to its environment. Until the grey squirrel arrived, that is, and proved itself rather better adapted to broadleaf forests thanks, in part, to its ability to digest acorns.
There are many reasons why evolution does not produce "designs" that are as good as they could be. Natural selection's only criterion is that something works, not that it works as well as it might. Botched jobs are common, in fact. The classic example is the panda's thumb, which it uses to grasp bamboo. "The panda's true thumb is committed to another role. So the panda must... settle for an enlarged wrist bone and a somewhat clumsy, but quite workable, solution," wrote Stephen Jay Gould in 1978.
As this example shows, evolution is far more likely to reshape existing structures than to throw up novel ones. The lobed fins of early fish have turned into structures as diverse as wings, fins, hoofs and hands. We have five fingers because our amphibian ancestors had five digits, not because five is necessarily the optimal number of fingers for the human hand.
Many groups simply never evolve features that might have made them even more successful. Sharks lack the gas bladder that allows bony fish to control their buoyancy precisely, for example, and instead have to rely on swimming, buoyant fatty livers and, occasionally, a gulp of air. Similarly, mammals' two-way lungs are far less efficient than birds' one-way lungs. And sometimes creatures evolve features that actually reduce their overall fitness rather than increase it, such as the peacock's tail (see Evolution always increases fitness).
Use it or lose it
Continual mutation also means that if you don't use it, you lose it. For instance, many primates cannot make vitamin C, because of a gene mutation. This mutation makes no difference to animals that get plenty of vitamin C in their diet. However, when the environment changes, such loss of function can make a big difference, as one primate discovered on long sea voyages.
Evolution's lack of foresight can produce inherently flawed designs. The vertebrate eye – with its back-to-front wiring and blind spot where the wiring goes through the retina – is one example. Later adaptations have compensated for these problems to a large extent but once natural selection fixes upon a flawed, but workable, design, a species' descendants are usually stuck with it.
An organism's fitness is also relative to its environment, which is usually changing. There is a constant arms race going on between predator and prey, parasite and host. Many species have to evolve continuously just to maintain their current level of relative fitness, let alone get fitter. As the Red Queen says in Through the Looking Glass: "It takes all the running you can do, to keep in the same place."
Evolution's peak?
Humans are not running fast enough. Evolving through natural selection is about time and numbers. The number of new mutations that appear, and the number of chances that natural selection has to eliminate the harmful and favour the beneficial ones, depends on the size of a population, the number of offspring each individual has and on the number of generations, among other things.
We might like to think of ourselves as the most "highly evolved" species but, in terms of how many rounds of mutation and selection we've undergone, we are one of the least evolved species.
Around 10 billion new viral particles can be produced every day in the body of a person infected with HIV. By contrast, the total human population on Earth was no more than a few million until a few thousand years ago.
Furthermore, in a decade bacteria can produce 200,000 generations -- about the number of generations of humans there have been since our lineage split from that of chimpanzees. So it's hardly surprising that in less than a human lifespan we’ve seen the evolution of new diseases such as HIV and numerous antibiotic-resistant bacteria.
Although human evolution has sped up in the past 10,000 years, we are changing our environment faster still. As a result, instead of becoming better adapted we are actually becoming less well adapted to the world we are creating. Think of the huge range of modern afflictions, from obesity and allergies to short-sightedness and drug addiction, we suffer from. Viruses and bacteria might approach perfection, but we humans are at best a very rough first draft.
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The phrase "survival of fittest" is widely misunderstood (see 'Survival of the fittest' justifies everyone for themselves). Many wrongly assume it means that evolution always increases the chances of a species surviving.
Evolution sometimes results in individuals or populations becoming less fit and may occasionally even lead to extinction.
There are several ways in which evolution can reduce the overall fitness of individuals or of populations. For starters, natural selection can take place at different levels – genes, individuals, groups – and what promotes the survival of a gene does not necessarily increase the fitness of the individuals carrying it, or of groups of these individuals.
For example, parasitic DNA elements, or transposons, can spread through a population even though they make their host organisms less fit. Transposons are one cause of genetic diseases such as haemophilia.
Similarly, selfish individuals may thrive at the expense of altruistic individuals in a group – making them the "fittest" – even though they make the group as a whole less competitive. Such cheaters can have disastrous consequences.
In 1932, J. B. S. Haldane suggested this could even lead to the extinction of populations – a phenomenon called evolutionary suicide. Models and some experimental evidence suggest he was right.
For instance, when nutrients run low, individual myxobacteria (slime bacteria) may come together to form a fruiting body to produce spores. Lab studies have shown that cheating myxobacteria that only produce spores and never help form the non-spore producing parts of the fruiting body can drive populations to extinction.
Genes capable of driving populations to extinction might have a practical use, however. Biologists are exploring the possibility of releasing engineered parasitic DNA into populations of malaria-carrying mosquitoes.
There is concern that something similar could happen accidentally. Fish that have been genetically modified to produce a growth hormone grow faster and larger, mature earlier and produce more eggs. But they are less likely to survive in the wild than unmodified fish. According to the Trojan gene hypothesis, a gene variant that produces such characteristics could spread rapidly through a wild population despite reducing individual fitness, and eventually drive the population to extinction.
Another way in which evolution can reduce a species' chances of survival is through the accumulation of detrimental mutations. Mutations provide the vital raw material for natural selection, so if the mutation rate is too low a population will not be able to evolve fast enough to keep up with environmental changes.
If, on the other hand, a population's mutation rate is too high, detrimental mutations may accumulate faster than natural selection can eliminate them. Eventually, the number of mutations can exceed the "error catastrophe threshold", again leading to the extinction of a population.
In theory, any species with a very small population could accumulate deleterious mutations faster than it can eliminate them. The problem is especially severe for asexual organisms such as the Amazon molly – an effect known as Muller's rachet.
It is far less of a problem for sexually reproducing species because the exchange of genetic material between chromosomes can separate good and bad mutations. Some unlucky offspring get saddled with lots of nasty mutations and die out, while the lucky ones get hardly any.
In theory, a mutation catastrophe can also occur as a result of linkage. This refers to gene variants that are inherited together because they sit next to each other on a chromosome. Suppose a mutation that greatly increases the mutation rate somehow ends up next to a new mutation that greatly increases fitness. The immediate fitness benefits of the beneficial mutation will initially mask the deleterious effects of the "mutator" mutation, meaning both mutations will rapidly sweep through a population, ultimately with disastrous consequences.
A few doctors hope to exploit mutation accumulation to treat diseases. Certain viruses such as HIV are already close to the error catastrophe threshold. Drugs that increase the mutation rate of the viruses still further might push them over the threshold and drive a population of viruses inside a person's body to extinction.
Finallly, it has long been recognised that the competition between members of the same species to reproduce – sexual selection – can favour traits that reduce a species' overall fitness. Male peacocks with the biggest and brightest tails might get the females' attention, but lugging around a heavy, conspicuous tail reduces their chances of survival.
Studies of threatened bird species suggest that sexual selection can indeed drive populations to extinction. Some biologists go so far as to blame sexual selection for the conspicuous consumption that threatens humanity's future.
According to the handicap principle, features such as peacocks' tails evolve precisely because they are disadvantageous. Consider an individual who is trying to signal to females how fit and strong he is. If the signal is easy to make, weaker males can easily cheat by making the same signal. But if making the signal is costly – such as growing a large, clumsy tail or giving away food – there's no way to cheat.
Proving that any of these phenomena have ever led to extinctions in the wild is far from easy, because any species to which this has happened are, of course, no longer around to study. The indirect evidence is growing ever stronger, though.
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At an individual level, it might not matter much. However, any modern society which bases major decisions on superstition rather than reality is heading for disaster
So your brother or mother is a creationist. Let them believe what they want, you might think. After all, it makes family get-togethers a lot easier and no difference to anyone else.
Or does it? Imagine if Mike Huckabee ends up as vice-president of the US – a mere heart attack away from the top job. Would you feel comfortable if the world's biggest superpower was run by a man who rejects evolution, thanks to the support of tens of millions of people who also refuse to accept the truth?
It is dangerous when leaders prefer dogma to biological reality: Stalin's support for the pseudoscience of Lysenko was a disaster for Soviet agriculture.
Evolving problems
The success of western civilisation is based on science and technology, on understanding and manipulating the world. Its continued success depends on this, perhaps now more than ever.
Any leader who thinks evolution is a matter of belief is arguably unfit for office. How can someone who dismisses the staggering amount of evidence for evolution assembled by researchers in myriad fields possibly evaluate more subtle scientific evidence for, say, climate change?
What's more, evolution is directly relevant to many policy decisions. Infectious diseases from tuberculosis to wheat rust are making a comeback as they evolve resistance to our defences. Antibiotic-resistant superbugs like MRSA are a growing problem. A deadly virus such as H5N1 bird flu or ebola might evolve the ability to spread from human to human at any time, leading to a devastating pandemic. It is not possible to grasp how serious these threats are and plan for them unless you understand the power of evolution.
There are many more subtle areas where understanding evolution matters too. For instance, fishing policies that allow fishermen to keep only large fish are actually leading to the evolution of smaller fish. The tremendous changes we are making to the environment are altering many species, from rats becoming resistant to poisons to urban birds changing their songs to counter noise pollution.
There is our future, too. Modern biology is on the brink of giving us previously unimaginable power over the human body, from reshaping embryos to rewriting the genetic code and delaying the effects of ageing. Societies' views on if and how these powers should be used will inevitably be shaped by people's understanding of their evolutionary origins. Things look rather different depending whether you think we are a perfect, finished product or crude early prototypes thrown up by a desperately cruel process from whose clutches we now have to break free.
This is not to say that evolutionary theory tells us how to run societies (see Survival of the fittest justifies everyone for themselves) or make ethical decisions (see Accepting evolution undermines morality). It doesn't. It is a descriptive science, not a prescriptive one. It does, however, help us to make informed decisions.
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The "fittest" can be the most loving and selfless, not the most aggressive and violent. In any case, what happens in nature does not justify people behaving in the same way
The phrase "survival of the fittest", which was coined not by Darwin but by the philosopher Herbert Spencer, is widely misunderstood.
For starters, there is a lot more to evolution by natural selection than just the survival of the fittest. There must also be a population of replicating entities and variations between them that affect fitness – variation that must be heritable. By itself, survival of the fittest is a dead end. Business people are especially guilty of confusing survival of the fittest with evolution.
What's more, although the phrase conjures up an image of a violent struggle for survival, in reality the word "fittest" seldom means the strongest or the most aggressive. On the contrary, it can mean anything from the best camouflaged or the most fecund to the cleverest or the most cooperative. Forget Rambo, think Einstein or Gandhi.
What we see in the wild is not every animal for itself. Cooperation is an incredibly successful survival strategy. Indeed it has been the basis of all the most dramatic steps in the history of life. Complex cells evolved from cooperating simple cells. Multicellular organisms are made up of cooperating complex cells. Superorganisms such as bee or ant colonies consist of cooperating individuals.
Suicidal cells
When cooperation breaks down, the results can be disastrous. When cells in our bodies turn rogue, for instance, the result is cancer. So elaborate mechanisms have evolved to maintain cooperation and suppress selfishness, such as cellular "surveillance" programmes that trigger cell suicide if they start to turn cancerous.
Looked at from this point of view, the concept of the survival of the fittest could be used to justify socialism rather than laissez-faire capitalism. Then again, the success of social insects could be used to argue for totalitarianism. Which illustrates another point: it is nonsense to appeal to the "survival of the fittest" to justify any economic or political ideology, especially on the basis that it is "natural".
Is cannibalism fine because polar bears do it? Is killing your brother or sister fine because nestlings of many bird species do it? Is murdering your children fine because mice sometimes eat their own pups? Is paedophilia fine because bonobo adults have sex with juveniles?
Powerful grip
Just about every kind of behaviour that most of us regard as "unnatural" turns out to be perfectly natural in some nook or cranny of the animal kingdom. No one can plausibly argue that this justifies humans behaving in the same way.
Yet even though such examples expose the utter absurdity of appealing to what is "natural" to judge right from wrong – the naturalistic fallacy – we seem to have a strange blind spot when it comes to evolution. Survival of the fittest has been claimed to justify all kinds of things, from free markets to eugenics. Such notions still have a powerful grip in some circles.
However, natural selection is simply a description of what happens in the living world. It does not tell us how we should behave.
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It might seem like there is no end to nature's inventiveness but there are some features that could probably never evolve, at least on Earth
It often seems that nature invented pretty much everything that can be invented long before humans arrived on the scene – including the wheel, kind of. There is a salamander living in the Californian mountains that coils itself up and rolls downhill when threatened, for example. The pearl moth caterpillar goes one better and can roll itself along a flat surface for four or five revolutions to escape predators.
Nevertheless, there are structures that would clearly be useful but have never evolved. Zebras with built-in machine guns would rarely be bothered by lions, some point out. So why can evolution invent some things but not others?
This is an extremely difficult issue to tackle: how can we study something that has not happened? One way to approach it is to start with a question used by those who deny evolution and believe that many of nature's inventions, such as the eye or the bacterial flagellum, are simply too complex to have evolved. What use is half a wing, they ask? (see Half a wing is no use)
Very useful, it turns out. The wings of insects might have evolved from flapping gills that were originally used for rowing on the surface of water. This is an example of exaptation – structures and behaviours that evolved for one purpose but take on a wholly new one, while remaining useful at every intermediate stage.
Come in, over
Turn this argument around, however, and it suggests that some features cannot evolve because a half-way stage really would be of no use. For example, two-way radio might be useful for many different animals, for making silent alarm calls or locating other members of your species. So why hasn't it evolved? The recent invention of nanoscale radio receivers suggests it is not physically impossible.
The answer might be that half a radio really is useless. Detecting natural radio waves – from lightning, for instance – would not tell animals anything useful about their environment. That means there will be no selection for mutations that allow organisms to detect radio waves. Conversely, without any means of detecting radio waves, emitting them would serve no useful purpose. Radar might not be able to evolve for similar reasons.
The contrast with visible light could hardly be greater. It is clear that simply detecting the presence or absence of light would be advantageous in many environments, that even a blurry picture is better than nothing at all, and so on right up to hawk-eyed sharpness.
Seaweed skies
Emitting visible light can be helpful too, even for creatures that cannot detect it themselves. For the bioluminescent phytoplankton that light up ocean waves, for instance, it is a way of summoning predators that eat the phytoplankton's enemies. A similar argument applies to sound: it is not hard to see how forms of echolocation evolved independently in groups such as bats, cave swiftlets and whales.
One might also wonder why plants that float in the sky like balloons have never evolved. The idea does not seem too far-fetched at first glance: many seaweeds have floats called pneumatocysts, filled with oxygen or carbon dioxide. Other algae can produce hydrogen. So fill a large, thin pneumatocyst with hydrogen and perhaps a seaweed could fly. Flying plants would beat water and land plants to the light, giving them a big advantage, so why aren't our skies filled with living green balloons?
Perhaps partly because large pneumatocysts with extremely thin membranes would be far more vulnerable to predators and damage from waves, so an intermediate stage could never evolve. What's more, algae produce hydrogen only when there's a lack of sulphur in the water, and in any case the molecules of hydrogen gas are so tiny that they would leak out of any pneumatocyst. Half a hydrogen balloon doesn't look very good for anything, at least on our planet. Even evolution has its limits.
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There are numerous evolutionary mechanisms that might explain homosexual behaviour, which is common in many species of animals
"Simple reasoning shows that evolution cannot explain homosexuality – how would a homosexuality gene get selected for?" "Why have the genetic traits predisposing to homosexuality not been eliminated long ago?"
Such arguments are surprisingly common – and completely wrong.
Homosexual behaviour has been observed in hundreds of species, from bison to penguins. It is still not clear to what extent homosexuality in humans or other animals is genetic (rather than, say, due to hormonal extremes during embryonic development), but there are many mechanisms that could explain why gene variants linked to homosexuality are maintained in a population.
A common assumption is that homosexuality means not having children, but this is not necessarily true, especially in cultures other than our own. Until it became acceptable for same-sex couples to live together in western countries, many homosexual people had partners of the opposite sex. In some traditional societies, various forms of non-exclusive homosexuality were common.
Reasons why
Among animals, homosexual behaviour is usually non-exclusive. For instance, in some populations of Japanese macaques, females prefer female sexual partners to male ones but still mate with males – they are bisexual, in other words.
It has also been suggested that homosexuality boosts individuals' reproductive success, albeit indirectly. For instance, same-sex partners might have a better chance of rising to the top of social hierarchies and getting access to the opposite sex. In some gull species, homosexual partnerships might be a response to a shortage of males – rather than have no offspring at all, some female pairs raise offspring together after mating with a male from a normal male-female pair.
Another possibility is that homosexuality evolves and persists because it benefits groups or relatives, rather than individuals. In bonobos, homosexual behaviour might have benefits at a group level by promoting social cohesion. One study in Samoa found gay men devote more time to their nieces and nephews, suggesting it might be an example of kin selection (promoting your own genes in the bodies of others).
For your health
Or perhaps homosexuality is neutral, neither reducing nor boosting overall fitness. Attempts to find an adaptive explanation for homosexual behaviour in macaques have failed, leading to suggestions that they do it purely for pleasure.
Even if homosexuality does reduce reproductive success, as most people assume, there are plenty of possible reasons why it is so common. For instance, gene variants that cause homosexual behaviour might have other, beneficial effects such as boosting fertility in women, as one recent study suggests, just as the gene variant for sickle-cell anaemia is maintained because it reduces the severity of malaria. Homosexuality could also be a result of females preferring males with certain tendencies – sexual selection can favour traits that reduce overall fitness, such as the peacock's tail (see Evolution always increases fitness).
Given that, until recently, homosexual behaviour in animals was ignored or even denied, it's hardly surprising that we cannot yet say for sure which of these explanations is correct. It could well turn out that different explanations are true in different species.
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The only thing that creationists agree on is that they don't like evolution. Even Genesis gives two contradictory accounts of creation
If someone tells you that creationism provides a better explanation for life on Earth than the theory of evolution, ask them which version of creationism.
Among creationists, there is an extraordinary range of beliefs about how life came to be. A few creationists accept that evolution produced the great diversity of life on Earth – apart from humans. Others think all life evolved but that the process was guided by a supernatural being.
Other creationists accept that evolution can lead to minor changes (microevolution) but deny that lots of little changes can result in new species or even new groups of organisms (macroevolution). Some think a deity created the very first life but then left it to evolve by itself.
Then there's the vexed issue of timing. "Young Earth Creationists" regard the Genesis account as "inerrant" despite its contradictions (see Evolution is wrong because the Bible is inerrant), and claim the planet was created about 6000 years ago. "Old Earth Creationists" meanwhile accept the hundreds of lines of evidence suggesting otherwise.
God, amok
This schism is just the beginning. Some don't dispute the earth's apparent age but believe it is an illusion (the omphalos hypothesis, which some summarise as "God faked it"). Yet others claim that the planet itself is billions of years old but that life on it was created only recently.
Creationists do at least all believe in a creator. But who is it: God, Allah, Yahweh, Brahma, Zeus, Olorun, aliens or a giant hermaphrodite?
Those who have studied our planet and the life on it, however, have come to very clear conclusions: the Earth is around 4 billion years old and all the life on it gradually evolved from much simpler forms. There is no evidence of any kind of outside intervention, and no need to invoke it to explain what is known. Yes, there are many debates among biologists, geologists and cosmologists over the finer details, but these will be resolved sooner or later by new discoveries or experiments. Reality is the ultimate arbiter.
By contrast, there is no way to resolve the often vast differences between the numerous forms of creationism. Anyone can come up with their own version of creationism (and many do). How do you convince the followers of the Flying Spaghetti Monster, for instance, that his noodle is not the real creator?
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#603 Posted by Skeptical on April 16, 2008 10:02:09 pm
Re: # 601
Well Nkg...
I have already said that religon is dogma....
And a problem is that dogma also tries to explain the evolution of the universe....
And those who profess faith unfortunately would try to profess beleif in its explanations...
You see the evolution or the qustion of being is he basic premise on which every religon stands...
It holds true for Islam, Christianity as well as Hinduism....
Well Nkg...
I have already said that religon is dogma....
And a problem is that dogma also tries to explain the evolution of the universe....
And those who profess faith unfortunately would try to profess beleif in its explanations...
You see the evolution or the qustion of being is he basic premise on which every religon stands...
It holds true for Islam, Christianity as well as Hinduism....
#602 Posted by tahir on April 16, 2008 7:24:24 am
Re: # 595
Admitting and declaring openly who one is without being afraid is not KUFR!
I did so because I did not want anyone to ask me what I believed in.
As for your disappointment with the doctor who deals with the brain-dead, well, he revealed who he really is, didn't he?
Pray for the cryogenically frozen editors of CHOWK, the vile satanic interacters, and their supporters. That's all one can do for them.
Peace.
Admitting and declaring openly who one is without being afraid is not KUFR!
I did so because I did not want anyone to ask me what I believed in.
As for your disappointment with the doctor who deals with the brain-dead, well, he revealed who he really is, didn't he?
Pray for the cryogenically frozen editors of CHOWK, the vile satanic interacters, and their supporters. That's all one can do for them.
Peace.
#601 Posted by nkg on April 16, 2008 3:14:49 am
Zeemax...
Enough. You ugly hindoo achoot, now go home and lie down with your ugly wife and produce ugly babies to populate your hindia.
Shut up now.
Ans: Ha ha ha...true muslim/scoundrel/barbarian....
Skeptical...
Khair I think the central problem is that religon is based upon unquestionable faith and those who profess to adhere will always be offended if its basic tenanats are questioned....
Ans: If you know that it is pure faith accept it. Don't try to prove that as truth with uttermost arrogance...There is no better explanation than evolution theory about the animal and plant world. Bible/Genesis can not explain existance of human life in South America, North America, Japan, Australia, China,North Europe, through this Adam & Eve theory. Human existance in these places are more than 5000 years old.
...
Coming to identity; it should not make people narrow minded. Broader the identity people take, better he/she becomes...
Enough. You ugly hindoo achoot, now go home and lie down with your ugly wife and produce ugly babies to populate your hindia.
Shut up now.
Ans: Ha ha ha...true muslim/scoundrel/barbarian....
Skeptical...
Khair I think the central problem is that religon is based upon unquestionable faith and those who profess to adhere will always be offended if its basic tenanats are questioned....
Ans: If you know that it is pure faith accept it. Don't try to prove that as truth with uttermost arrogance...There is no better explanation than evolution theory about the animal and plant world. Bible/Genesis can not explain existance of human life in South America, North America, Japan, Australia, China,North Europe, through this Adam & Eve theory. Human existance in these places are more than 5000 years old.
...
Coming to identity; it should not make people narrow minded. Broader the identity people take, better he/she becomes...
#600 Posted by Skeptical on April 15, 2008 10:51:31 pm
Well the amount of heat this article has generated is enormous....
Khair I think the central problem is that religon is based upon unquestionable faith and those who profess to adhere will always be offended if its basic tenanats are questioned....
The funny thing is that their lives are full of contradictions of the preaching of religon.....
They dont often practice the those teaching which require moulding of the lives...
And yet are ferocious when a basic tenanat is even indirectly questioned......
Any how even then I think religon should not be abused on websites because it will also strenghten the reactionary elements..
Religon like ethinicity is identity....
or at least a part of identity...
After all even Einstien became proud of his faith despite being Athiest when jews were attacked...
Khair I think the central problem is that religon is based upon unquestionable faith and those who profess to adhere will always be offended if its basic tenanats are questioned....
The funny thing is that their lives are full of contradictions of the preaching of religon.....
They dont often practice the those teaching which require moulding of the lives...
And yet are ferocious when a basic tenanat is even indirectly questioned......
Any how even then I think religon should not be abused on websites because it will also strenghten the reactionary elements..
Religon like ethinicity is identity....
or at least a part of identity...
After all even Einstien became proud of his faith despite being Athiest when jews were attacked...
#599 Posted by akcheema on April 15, 2008 12:25:02 am
Re: # 598; Tahir
so I am a 'monkey' or a 'pig' now, am I? you need to get over your paranoia first before we can talk civily. I think there is enough of that on this site as it is.
Take care; just don't get carried away with negative emotions my friend
so I am a 'monkey' or a 'pig' now, am I? you need to get over your paranoia first before we can talk civily. I think there is enough of that on this site as it is.
Take care; just don't get carried away with negative emotions my friend
#598 Posted by tahir on April 14, 2008 5:55:40 am
Dear brothers in faith,
Don't let CHOWK's new look fool you into thinking that some 'new management' has taken over and that things will suddenly improve. If they do at all, let it be known that I have repeatedly requested CHOWK editors to MODERATE and control the RAW-agents who have nothing better to do than analyse Pakistani news and then stoop to abusing Islam and the Prophets by pretending to be interacters!
There is deathly silence at the editor's desk. Surprised? Not only this, they are guilty of killing quite a few of my articles over the years! I beleive, they still have not received the 'security clearance' to publish them.
One door closes but many others will open. CHOWK is not the final frontier; that it has degenerated into a hate-site should not come as a surprise to those who have turned it into one.
One evening's worth of search reveals that these anti-Islam half-humans will not reform. They are nicely linked; most 'kufr' is anyway. That goodnes stands squabbling amongst itself is a sad situation and I expect that born-Muslim interacters here will remember who they are, where they come from, and where they might be headed if they join hands with 'highly-educated satans'.
Indeed, the Qur'an calls all such persons who lapse into utter unbelief 'monkeys' and 'pigs'. Why? Because the outward behaviour and moral decadence begins to resemble that of such animals.
I must thank those who stood up for me, and those who even thought of doing the same but were afraid of being ridiculed or abused.
There are three kinds of men in this world; fighters, collaborators, and traitors.
See where you fit!
Regards.
Don't let CHOWK's new look fool you into thinking that some 'new management' has taken over and that things will suddenly improve. If they do at all, let it be known that I have repeatedly requested CHOWK editors to MODERATE and control the RAW-agents who have nothing better to do than analyse Pakistani news and then stoop to abusing Islam and the Prophets by pretending to be interacters!
There is deathly silence at the editor's desk. Surprised? Not only this, they are guilty of killing quite a few of my articles over the years! I beleive, they still have not received the 'security clearance' to publish them.
One door closes but many others will open. CHOWK is not the final frontier; that it has degenerated into a hate-site should not come as a surprise to those who have turned it into one.
One evening's worth of search reveals that these anti-Islam half-humans will not reform. They are nicely linked; most 'kufr' is anyway. That goodnes stands squabbling amongst itself is a sad situation and I expect that born-Muslim interacters here will remember who they are, where they come from, and where they might be headed if they join hands with 'highly-educated satans'.
Indeed, the Qur'an calls all such persons who lapse into utter unbelief 'monkeys' and 'pigs'. Why? Because the outward behaviour and moral decadence begins to resemble that of such animals.
I must thank those who stood up for me, and those who even thought of doing the same but were afraid of being ridiculed or abused.
There are three kinds of men in this world; fighters, collaborators, and traitors.
See where you fit!
Regards.
#597 Posted by akcheema on April 12, 2008 4:19:57 pm
Re: # 595; Zeemax
only after his assertions about the kadianis; fair dos I have no love lost but don't like bringing in the jews to blaim everytime the Ummah has issues!
only after his assertions about the kadianis; fair dos I have no love lost but don't like bringing in the jews to blaim everytime the Ummah has issues!
#596 Posted by arjun_5 on April 12, 2008 11:44:25 am
#578 Posted by izuber on April 11, 2008 11:55:53 am
Mirzai's the seedling sowed by British Jews!
How could a person who died in the toilet head down be considered a spiritual leader of the level he and his cronies claim to be?
what about a child rapists who married his daughter in law?
Mirzai's the seedling sowed by British Jews!
How could a person who died in the toilet head down be considered a spiritual leader of the level he and his cronies claim to be?
what about a child rapists who married his daughter in law?
#595 Posted by zeemax on April 12, 2008 10:38:57 am
akcheema,
Did you call taher saheb an imbecile? Didn't expect that from you - since after all, I thought you had some class amongst garbage. I hope I wasn't wrong.
Did you call taher saheb an imbecile? Didn't expect that from you - since after all, I thought you had some class amongst garbage. I hope I wasn't wrong.
#594 Posted by zeemax on April 12, 2008 10:36:02 am
nkg,
Enough. You ugly hindoo achoot, now go home and lie down with your ugly wife and produce ugly babies to populate your hindia.
Shut up now.
Enough. You ugly hindoo achoot, now go home and lie down with your ugly wife and produce ugly babies to populate your hindia.
Shut up now.
#593 Posted by nkg on April 12, 2008 3:58:32 am
http://www.thedailystar.net/story.php?nid=31858
Those who blame American conspiracy etc...please check...
Those who blame American conspiracy etc...please check...
#592 Posted by nkg on April 12, 2008 3:56:01 am
Tahir...
Little more...
I have stayed in a muslim house for more than 2 years. They had no son. I was (to what ever possible extent) ingrained within the family. Neither they have objected my Saraswati Puja, nor I have taunted them for animal sacrifice...
Coming to Muhammed matter, the similar opinion you will find about Bal Thackery & Siv Sena; Advani and his various Ratha Yatras; CPI(M) and their corruptions. Public figures will always be subject to scrutiny. I am not sure, whether you have access to watch "Devil's Adviocate" of CNN-IBN. Mocking our Gods (Krishna, Rama etc...) are very popular in many part of India. Unfortunately, people like you are also gaining ground in India (Baroda art galary, Taslima Nasreen etc...)...
Little more...
I have stayed in a muslim house for more than 2 years. They had no son. I was (to what ever possible extent) ingrained within the family. Neither they have objected my Saraswati Puja, nor I have taunted them for animal sacrifice...
Coming to Muhammed matter, the similar opinion you will find about Bal Thackery & Siv Sena; Advani and his various Ratha Yatras; CPI(M) and their corruptions. Public figures will always be subject to scrutiny. I am not sure, whether you have access to watch "Devil's Adviocate" of CNN-IBN. Mocking our Gods (Krishna, Rama etc...) are very popular in many part of India. Unfortunately, people like you are also gaining ground in India (Baroda art galary, Taslima Nasreen etc...)...
#591 Posted by akcheema on April 12, 2008 3:38:52 am
Re: # 590; nkg sahib
the man is an imbecile; you know better than that!
Cheers
the man is an imbecile; you know better than that!
Cheers
#590 Posted by nkg on April 12, 2008 3:37:06 am
Re: # 584
Tahir...
Scoundrel...Who are you to tell me, what should I post and what not? Keep your blasphemy, hudood concepts within your barbaric country...I have never used any abusive language. The words paedophile, rapist, cheat, liar are generic english terms, which has well defined....
You don't need to bother about my peace or peace in Bangalore...Look after your own country and community first...
Tahir...
Scoundrel...Who are you to tell me, what should I post and what not? Keep your blasphemy, hudood concepts within your barbaric country...I have never used any abusive language. The words paedophile, rapist, cheat, liar are generic english terms, which has well defined....
You don't need to bother about my peace or peace in Bangalore...Look after your own country and community first...
#589 Posted by HPsauce on April 12, 2008 1:03:22 am
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