Evolution 101

Sometime in 1991, when I was still in graduate school, I attended a meeting of the Muslim Students Association at Duke University in
Durham, North Carolina. About thirty people were present. There was a reading from the Quran followed by a discussion. I forget the exact
passages that were read, but somehow the topic of evolution came up. I was surprised by what happened next. Several people mocked
the idea of biological evolution, dismissing it as implausible, even comical. Most of the people at that gathering were undergraduates born
and raised in America; a few were off-the-boat desis like myself, physicians, engineers, business-school types. As the only biologist
present, I tried to convey the notion of evolution as bona fide scientific truth, but nothing I said was seriously entertained. I was
dumbfounded. This was not my dada’s generation - these were twenty-somethings who had risen to the stratosphere of the American
educational system but who were still denying that life forms on Earth had evolved from each other over time.

Then, and in the years since, I have realized that the idea of biological evolution - the proposition that all living things can be traced
back in time to a common origin - is an awkward intellectual blind spot for even the most informed Muslims. I have two main motives for
writing this article. First, if you are curious about evolution and want to know what all the fuss is about, you’ll get the important facts here.
Second, and perhaps more important, if you don’t believe in biological evolution, I hope this article will convince you of it.

The theory of biological evolution was proposed by Charles Darwin as an explanation for the diversity of life forms on our planet. The
‘species’ is the elementary unit in the classification of living things. Members of a species differ from each other in only very minor ways
and are able to reproduce with each other. All humans are one species, for example, but they differ from chimpanzees and gorillas, which
are separate species. Every form of life can be classified into a species, be it animal, plant, insect or germ. The diversity of life is
staggering: there are an estimated 30 million distinct species on Earth, of which less than 10% have so far been described! Surely such
immense biological variety calls for an explanation. The traditional view has been that each kind of living creature was specifically
designed by divine intent. This idea has been refuted in that there is now overwhelming evidence to confirm that, over many generations,
new species have arisen from existing ones. This is the central tenet of evolutionary theory. One implication of this conclusion is that
humans, if they go back far enough, can trace their ancestry to apes - a suggestion that many people find offensive. However, not only is
it true that we have descended from apes, if you go back far enough in geological time, you can indeed trace your family tree all the way
down to germs.

In 1859, Darwin published "On the Origin of Species by Means of Natural Selection," in which he proposed that complex life forms have
evolved from simpler life forms under pressure from environmental constraints that conferred differential survival advantage. According to
this thesis, living creatures are involved in a constant struggle to survive on limited resources and natural variation within a species can
confer, by chance, a survival advantage on some members of that species. A series of such events, Darwin argued, leads to life forms
sufficiently different from the parent species (i.e. a new species) resulting, over time, in the diversity of life that we see on our planet.
Because of its implications about human origins, the book provoked a storm of controversy. In many social and intellectual circles Darwin
was vilified, but accumulating scientific evidence has proved him to be right. An anti-evolution sentiment remains widespread, however
(as evidenced by that MSA meeting at Duke). In the United States, some state legislatures maintained a ban on the teaching of evolution
in schools well into the twentieth century. Indeed, it was only as recently as 1968 that the US Supreme Court declared any such ban
illegal.

Evidence in favor of evolution comes from four major sources. The simplest line of evidence is the fossil record. A fossil is the remains of a
life form preserved in rock. The age of a fossil can be reliably determined by radioactive dating techniques. The fossil record of life on
Earth shows that the simpler a fossil, the older it is. This suggests an orderly increase in the complexity of life with the passage of
geological time. For example, the earliest known fossils are over 3 billion years old and comprise microscopic life forms, such as bacteria;
the first vertebrates (creatures with backbones) appear in fossils that are 400 million years old; the first mammals in fossils that are 200
million years old; and the first apes in fossils that are 50 million years old. (By contrast, our own species, Homo sapiens, is very much the
new kid on the block, having evolved only 100, 000 to 200, 000 years ago.)

The second major line of evidence is homology in structural design. For example, the skeletons of a human arm and a bat’s wing are
composed of the same structural elements, adapted in each case to the specialized demands of the species. There is a common theme of
design, which suggests a common origin. A special example of homology are the so-called vestigial organs, which are important
structures in some species but persist as functionless relics in more advanced life forms. The classic example is the human appendix,
which is a part of the intestine specialized for digesting cellulose and is best developed in animals that eat grass, such as rabbits. In
humans, this organ is a small and useless outpouching from the human gut that serves no purpose except to create mischief when it gets
inflamed, producing appendicitis. The existence of the appendix in both humans and rabbits, unnecessary in one yet critical in the other,
suggests a common origin for the two species.

The third major line of evidence comes from embryology, which is the study of living things that haven’t been born, like the human fetus or
the egg of a chicken. The embryos of creatures as varied as chickens, lizards and humans share common important features. That such
diverse organisms should go through the same stages in their early development from conception to birth argues for evolutionary ancestry
from a common source.

The capstone in the body of evidence supporting evolution is molecular biology. This is the study of the molecular basis of life. All living
things are made up of cells, which are tiny, microscopic chambers behaving as semi-independent functional units. The human brain is
made up of a billion brain cells, for example, and a human liver is made up of millions of liver cells. All cells, from creatures as complex as
humans or as simple as earthworms, work with the same basic molecular machinery. In fact, one critical component of cells, the
mitochondrion, looks and behaves for all purposes like bacteria, representing some kind of evolutionary signature of bacteria infecting
other cells. That the cells of all living things have the same basic design strongly argues for a common origin of life. But it gets even
better. The most convincing argument comes from DNA, the molecule of heredity. In 1944, Oswald Avery showed that the basis of
heredity is the transmission of a chemical - deoxyribonucleic acid or DNA - from parent to offspring. In 1953, Watson and Crick solved
the chemical structure of DNA and things have never been the same. DNA has four important chemical components, symbolized by the
letters A, G, T and C. Each DNA molecule is a long string in which these components are linked to each other in a specific sequence (for
e.g., A-A-G-C-C-T-A-G, etc.). The ability of a DNA molecule to carry information lies in its particular sequence of these components,
which represents a code that can be biochemically translated into unique proteins. This is the language of genetic transmission. The
proteins, in turn, effect the processes of life. The comparison of DNA from diverse life forms demonstrates remarkable sequence similarity,
thus providing a magnificent confirmation of the theory of evolution. The DNA of humans and chimpanzees, for example, is 98% identical;
it took many millions of years to produce the 2% divergence. Advances in molecular biology are an incredibly powerful development. The
comparative analysis of DNA sequences can precisely reconstruct not only the evolutionary lineage of all life forms but also the distance
that separates them in geological time.

Biological evolution is a certainty, indeed as much of a certainty as gravity, atoms, and planetary motion. To deny evolution is to deny
credible, convincing evidence - it is as ludicrous as saying that the Earth is flat. Nevertheless, some very important features of life on
Earth remain unexplained. First, since the biological basis of human consciousness is unknown, evolutionary theory provides only
conjectural insights into the emergence of human intelligence. Although many species in transition between chimpanzees and humans
have been recovered in fossil form (such as Homo habilis and Homo erectus), whatever we can know of the minds of these hominids will
remain sparse and indirect. Second, evolutionary theory does not explain the origin of life. Evolution shows how the complex
heterogeneity of life has come about according to natural laws, but it has no capacity to address how life itself came about in the first
place, which remains utterly mysterious. Third, the notion of chance genetic variation as the sole ultimate basis for the complexity of living
things is probably simplistic. This does not argue against evolution; it simply suggests that there may be more to the mechanism of
biological evolution than just the Darwinian concept of natural selection.

I am a Muslim and I accept the theory of biological evolution. At the same time, I can see how this idea can offend and how it can be
misconstrued as being in conflict with Quranic statements. Nevertheless, I would submit, with respect, that denying the phenomenon
would be irrational. I am not going to refer you to parts of the Quran or Hadees that contradict evolution, or parts that uphold it. I think it is
pointless to take recourse to words in a religious text in order to validate or invalidate the observation of natural phenomena. Different
people can always find different meanings in the same words, which is why observations that pass the rigors of the scientific method must
supersede any convictions based on the interpretations of language. The burden of proof, in other words, is no longer on Charles Darwin.