The Chronicle: 4/7/2006: The Case for Evolution, in Real Life

The Chronicle: 4/7/2006: The Case for Evolution, in Real Life: "By DAVID P. BARASH

Noting the role of the Royal Air Force in saving his country during the Battle of Britain, Winston Churchill observed that never had so many owed so much to so few. We owe a great deal — indeed, literally everything — to evolution, and yet never have so many said and written so much about something they understood so poorly. Not that evolution is all that difficult to understand. Rather, so many people have such strong feelings about it, often connected to so many regrettable stock phrases, that clear thought has often been obscured. This is especially unfortunate in today's intellectual — or, more to the point, anti-intellectual — climate, with the Bush administration persistently seeking to trump science with ideology.

Notwithstanding recent victories of science over so-called intelligent design in Pennsylvania and Utah, this particular struggle is not likely to end soon. The following catalog of misconceptions, along with responses, is therefore offered for scholars who may well find themselves confronting voices whose amplitude and frequency exceed their wisdom.

'It's only a theory.' Biologists often speak of 'the theory of evolution,' but not because evolution is a guess or mere speculation. My Random House Dictionary provides, among its definitions of "theory," the following: "a proposed explanation whose status is still conjectural, in contrast to well-established propositions that are regarded as reporting matters of actual fact." Someone might express a "theory" that Elvis Presley still lives, or that trailer parks attract tornadoes. The same person might also say, "Biologists have a theory that human beings evolved," in which case, knowingly or not, a very different use of the word has been employed. Indeed, my dictionary also gives this definition of "theory": "a more or less verified established explanation accounting for known facts or phenomena," with examples that include number theory, the theory of relativity, atomic theory, and so forth. In this sense, and this only, evolution is a theory. It is, in fact, as close to truth as any science is ever likely to get. (And, proudly situated in the old-fashioned, pre-postmodernist tradition, I assert that this is very, very close indeed.)

"Evolutionary logic is circular: The fittest are those that survive, and those that survive are the fittest. So it doesn't say anything." First, natural selection is not about survival, but reproduction: specifically, individuals' and genes' reproducing themselves. Survival is evolutionarily important because — and only because — it contributes to reproduction. Second, "fitness" does not determine natural selection; rather, natural selection is the unavoidable result of how "fit" something is, which is to say, how successful it is in promoting its genes. Fitness leads to the important prediction that natural selection favoring a particular type should result in a larger proportion of that type in future populations. This prediction has been repeatedly tested and confirmed.

"Natural selection is just a negative process; it cannot create anything new." Natural selection is only "negative" in that certain individuals and their genes fall by the evolutionary wayside in preference to others, which prosper. But evolution is not merely a question of deleting those organisms that are less fit; because of mutation (which provides genetic novelty) and sexual reproduction (which combines DNA in unique ways), new genetic material is constantly being produced. And much depends on this regular generation of genetic diversity, on the world being, as the poet Louis MacNeice put it, "incorrigibly plural." In his poem "Snow," MacNeice went on to feel "the drunkenness of things being various," a variousness that is essential as the building blocks from which evolution constructs those things that we identify as highly adapted organisms, including ourselves.

But although the production of diversity is fundamentally random, the power of natural selection is that it is not simply at the mercy of haphazard events, merely eliminating the unfit. It creates novelty because it adds a crucial process: a mechanism for "selective retention."

Imagine that instead of those hypothetical monkeys creating all of Shakespeare, we wanted just a single phrase, "to be or not to be." It consists of 18 characters, including spaces. Given the alphabet plus a possible blank space, we have a total of 27 possibilities for each slot. The chance that one of our monkeys might randomly get the initial "t" is thus 1/27. The chance that it would simultaneously and randomly place an "o" in the second slot is 1/27 x 1/27 = 1/729. The chance of getting all 18 characters correct, by chance alone, is thus 1/27 times itself 17 times, which is inconceivably small. (The following analysis, with some modification, was inspired by Richard Dawkins's superb book The Blind Watchmaker.)

But what if, instead of tossing out every meaningless word and having to start afresh each time, those patterns that were promising — even by a little bit — were retained, and then randomly modified yet again, once more retaining (that is, selecting) those that were more "fit"? I started with 18 random strikes on a computer keyboard and programmed the machine to make a few small changes — introduce some new letters — every "generation." Those changes are equivalent to mutation and sexual recombination, providing regular sources of random variation on an existing theme. Next I added the simple requirement of selectively retaining whatever most closely approximates "to be or not to be," after which the "organism" randomly varies again, with the outcome screened once more for resemblance — however slight — to the target. The result was that after a very small number of generations — usually on the order of 30 — the desired outcome was obtained.

In one test, for example, I started with "fuwl sazgh ekm fje." Discouraging, perhaps, but after several runs it had become the dimly recognizable "tubl hot nnoq ioby." By run 22, it was "tu bep ok not ts e." And by 29, "to be ok not to bo," which even the most cynical monkey is likely to acknowledge as having just about arrived, and a whole lot more quickly than 1/27 to the 18th power would suggest.

Starting with gobbledygook, and using only random variation and selective retention, something new had been created, something so nonrandom, in fact, that it is perhaps the most famous phrase in the English language! One might object, of course, that there is a crucial added factor: Human intelligence was injected into the process. For example, "to pee or not to pee" is also syntactically correct — and an appropriate query on certain occasions — but is unlikely to have echoed down the corridors of literature for 400 years.

Shakespeare presumably considered various possible alternatives to Hamlet's renowned dilemma, although he assuredly didn't puzzle through every option. Like a human chess master, as opposed to IBM's chess-playing program, Deep Blue, a creative intellect takes numerous shortcuts. But this, too, is very much what natural selection does. Living things offer only a very limited subset of what is possible. Instead of a creative human intelligence rejecting certain verbal combinations over others, the environment faced by every living thing rejects certain genetic combinations over others. In arid conditions, it rejects combinations that waste water; in cold conditions, it rejects combinations that waste heat. Among predators it rejects combinations that are clumsy at stalking their prey, while among prey species, it rejects those that are incautious or inept when it comes to avoiding their predators. As Robinson Jeffers put it, in "The Bloody Sire":

What but the wolf's tooth whittled so fine

The fleet limbs of the antelope?

What but fear winged the birds, and hunger

Jeweled with such eyes the great gos hawk's head?

The fleet limbs of the antelope, the wings of birds, and the eyes of the goshawk are all marvels of natural design, in no way inferior to the human design of Hamlet's melancholy question. And to understand how these were created, we need only understand how natural selection, based on random building blocks, can nonetheless generate highly nonrandom results.

"Evolution is no longer going on, especially in the case of human beings." Evolution happens anytime there are changes in a population's genetic makeup. The most powerful mechanism of evolutionary change is natural selection, which operates whenever some individuals leave more genetic representatives than others do. The only way for evolution to cease would be if everyone reproduced equally; more precisely, if genes continued to replace themselves in exactly the same proportion as they currently exist. Just a moment's reflection should convince anyone that evolution is very alive, for human beings as for everything else, so long as "differential reproduction" is going on.

That doesn't mean, however, that the conditions of evolution are the same as they have been in the past. The "selective environment" for human beings, for example, has changed dramatically from the Pleistocene. Certain traits that almost certainly were strongly selected against, such as myopia and diabetes, are now neutral or, at worst, only mildly negative. Human ingenuity has come up with eyeglasses and insulin, which only scratch the surface of how modern Homo sapiens has modified natural selection, hence its own evolution. Whereas it might have been selectively advantageous to be a good hunter, gatherer, or mastodon-avoider, now it is selectively advantageous to be able to reproduce despite strontium-90 in our bones or DDT in our fat, and, perhaps, to be positively attracted to ideologies that are unsympathetic to birth control. In any event, we have changed our own evolution, but not ended it.

"Biological evolution no longer matters, having been superseded by cultural evolution." Cultural evolution is real, and it may in fact be the one sense in which human beings do experience Lamarckian evolution, via a kind of inheritance of acquired characteristics. Cultural evolution, like biological evolution, involves change, but instead of genes, it is based on cultural practice: language; technology; styles of clothing; ways of living; traditions including culinary, religious, military, intellectual, social, sexual; and just about everything else that human beings do outside the anatomy and physiology of their own bodies. Cultural evolution, like biological evolution, requires variation, but instead of genetic mutations, its raw material comes from ideas and concepts, innovations of mind and matter that may ultimately be traceable — however indirectly — to humanity's DNA, but which are not a simple matter of biochemical alterations in genetic material. Cultural evolution, like biological evolution, proceeds by selective retention of whatever works or is favored for any other reason (such as obvious efficiency, the vagaries of fashion, or even the dictates of the powerful). Most important, cultural evolution, because it is Lamarckian and can be "inherited" nongenetically and passed on to others within a single generation, is much faster than biological evolution. To some extent, human beings are like a train traveling on two tracks, but in our case, the wheels on one track (biological evolution) move slowly while those on the other (cultural evolution) move rapidly. No wonder our species feels pulled apart. But this disparity, rather than negating the impact of biological evolution, only italicizes its significance.

"Evolution acts for the good of the species." All sorts of things evolve: galaxies, stars, a person's thinking, a government's policies. But none of those qualify as evolution as biologists understand the term. People have evolved; a person does not. Evolution involves change, but not the change that takes place in growth, aging, changing one's clothes or even one's mind. To qualify as biological evolution, there must be a change in a population's gene pool over time. This is why only populations evolve, not individuals — because each of us is stuck with our private genetic endowment. And yet individuals are crucial to evolution, both individual bodies and individual genes. In fact, one of the most important and useful realizations of recent years is that evolution operates most strongly at the lowest possible levels, notably that of individuals and genes, not groups or species.

Natural selection works by differential reproduction, with some individuals and their genes more successful than others. A species is the sum total of its individuals and their genes. It has no metaphysical existence of its own, and, as far as can be determined, no one is looking out for the good of the species as a whole, although each component has been selected to look out for itself. Analogously, in a free-market society, individuals and corporations seek to maximize their profits; any larger-order benefit derived by the nation is simply the unintentional summed effects of all those private, enterprising activities going on at a lower level. In the world of living things, there is no one looking out for collective benefit, no equivalent to Medicare, the FBI, or the Department of Education. Indeed, because individuals and genes are selected to maximize their own fitness, with none of them looking out for the interest of the larger group, the overwhelming majority of species that have ever lived are now extinct. Furthermore, when a species is endangered and thus at risk of going under, there is no indication that its constituent individuals are especially inclined to deprive themselves for the good of the threatened whole, and every sign that living things do whatever it takes to promote their own success, not that of the species.

The good of the species is purely an artificial construct of human beings, who, identifying an emergent whole (for our own convenience), misguidedly assume that its component parts see things the same way. But, in fact, when species benefit and individual benefit collide, the latter invariably wins.

"We've never found the 'missing link.'" Mark Twain once said that it was easy to stop smoking; he had done it hundreds of times. Similarly, there is no missing link; there are hundreds of them, or thousands, or millions. Consider two points, representing different species, one of which gave rise to the other. Think of them as connected by a line, representing evolutionary continuity. Now add a third point, more or less midway, and call it "the missing link." Having located this missing link, have you finished your task and bridged the gap between the two points? Not at all. In fact, you have just produced at least two new "missing links." Fill in both of them and you are faced with four. Like the horizon, which constantly recedes if pursued, the discovery of transitional forms merely adds to the transitional forms not yet identified. Mathematicians say there is an infinite number of points between any two identified points on a line; presumably there are fewer than an infinite number of missing links, but the more we find, the more there are.

The foolishness of the concept "missing link" becomes clear when you consider that for there to be some sort of midpoint, one must specify the two ends. Granted that one is modern Homo sapiens. But what ancestral form, precisely, holds down the other end of the linked chain: an anthropoid ape, a monkey, a primate, a mammal, a primitive reptile, an early amphibian, a primordial vertebrate, a pre-Cambrian worm? The "missing link" between modern human beings and the Devonian fishes, for example, might be a pre-dinosaurian reptile.

Nonetheless, some people are truly bothered by what they see as the paucity of transitional forms in the fossil record. They might just as well, however, be impressed with how many have been found. This applies to forms ancestral to Homo sapiens just as it does to other species. Probably the closest to a "missing link" in the human evolutionary lineage is the famous fossil Lucy, a female Australopithecine ("southern ape") of the species Australopithecus afarensis, who stood about three feet tall and weighed about 66 pounds. Lucy is as much an intermediate between apes and people as can be imagined. But she isn't alone.

There are several other species of Australopithecus, some relatively slender and most if not all of them on the line that gave rise to Homo sapiens. Others are heavy-bodied and — with the 20/20 vision of hindsight — identifiable as evolutionary dead ends whose descendants eventually went extinct. There is also a growing list of species belonging to the genus Homo, including Homo habilis, which is pretty much a link between Lucy and us, just as Lucy is a link between ancient apes and modern human beings. Other found links include Homo erectus, remains of which are known from Asia as well as Europe. My purpose here is not to provide a detailed list of fossil prehumans, their dates, cranial capacities, or precise relationships — a Sisyphean task, at any rate, because new ones are constantly turning up. Rather it is to note the existence of many links between Homo sapiens and earlier, ancestral animals.

While it is alive, there is no way to identify a transitional form as such. Maybe its descendants will remain largely unchanged for millions of years, so that it is not transiting to anything else but is just something that evolved early and persisted late. Or maybe its descendants will go extinct, in which case it is transitional only to a dead end. Or maybe its descendants will be somehow recognizable in the present day, in which case it is transitional in the usual sense of the term. In any event, rather than missing, links are actually quite abundant.

"Disputes among evolutionary biologists show that the foundations of the enterprise are shaky." Exactly the opposite is true: Creative ferment is the stuff of science. Unlike theology, with which creationists are more familiar, science is founded on ideas, discovery, testing, and refinement rather than on presumably inerrant doctrines of faith. Disputes about the details of evolutionary fine-tuning, far from undermining the validity of evolution, are testimony to the vitality of the whole enterprise, since any worthwhile science raises more questions than it answers. Accordingly there is uncertainty as to whether evolution always proceeds gradually or is punctuated by occasional bursts of change, but no question that it proceeds, and that it does so by the accumulation of genetic modifications.

"Biologists have never actually witnessed natural selection causing an evolutionary change, so the whole enterprise is therefore conjectural." Wrong again. Evolution is slow, usually taking many thousands of generations. That is not surprising, since it takes time to accumulate an observable effect when, for example, a certain gene may enjoy an advantage of only one in one thousand over its fellows. Given enough time, such a "selection differential" will make a genuine difference — but no biologist has ever lived long enough to detect significant evolutionary change in sequoia trees, for instance, or blue whales, which take many years to produce even a single generation. Hence it is difficult to catch evolution in flagrante. But not impossible.

Famous cases involve so-called industrial melanism among English peppered moths, the evolution of antibiotic resistance among bacteria, and observations by Peter and Rosemary Grant of adaptive changes in beak shape among Galapagos finches as a result of continuing climate change. Admittedly we have yet to observe one species evolving into another, but that is simply because evolutionary change is slow compared with human life spans. Besides, there is nothing magical about one species' turning into another: Under the influence of artificial selection, people have caused St. Bernards and Chihuahuas, greyhounds and bulldogs to evolve.

The key point for our purposes is that once again natural selection has been shown to give rise to evolutionary change during a very short time scale. Of course, peppered moths amd finches' beaks may appear to be much ado about nothing, cases of evolution laboring mightily and then bringing forth mere trivialities. Such examples might seem a far cry from horses evolving from terrier-sized Hyracotherium to modern Budweiser behemoths, velociraptors arising from the swampy slime, or the human brain expanding from shrew-like insignificance to the crowning, cerebral glory of modern sapient humanity. All these have indeed happened, but to witness such major transitions directly, it is necessary to consult the fossil record. Nonetheless, all evolutionary journeys (including the big ones, so-called macroevolution) begin with small steps (so-called microevolution) and are nothing but their accumulated consequences, over time.

Finally, consider this, which I believe undergirds much opposition to evolutionary science, and which I present as distinct from the earlier misconceptions, since it is not a matter of scientific veracity but, rather, opinion: "Evolution is a put-down, diminishing the special status of human beings." At the bottom of much opposition to evolution, I suspect, lies a deeper anxiety, that of acknowledging our kinship with "lower" life forms. "In an aversion to animals," wrote the philosopher Walter Benjamin, "the predominant feeling is fear of being recognized by them through contact. The horror that stirs deep in man is an obscure awareness that in him something lives so akin to the animal that it might be recognized." That recognition does not need elaborate scientific backing; it is usually enough to look into a dog's eyes, an act which, interestingly, does not usually evoke horror.

In Civilization and Its Discontents, Sigmund Freud refers approvingly to a 19th-century German playwright, Christian Garber, who gave this advice to a would-be suicide: "We cannot fall out of this world. We are in it once and for all." That caution applies to us all: We'll eventually die, but aside from that, the world is irretrievably with us. We are stuck in the muck and glory of it all, living creatures among many, biological to the core, created by our biology no less than is a dandelion or a dolphin. We cannot fall out of it, nor is there any reason to do so. For Darwin there was "grandeur in this view of life," in which all living things are linked both by historical continuity — that is, common ancestry — and as the products of the same fundamental process: evolution.

David P. Barash is a professor of psychology at the University of Washington. His most recent book, written with Nanelle R. Barash, is Madame Bovary's Ovaries: A Darwinian Look at Literature, published last spring by Delacorte.

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Section: The Chronicle Review
Volume 52, Issue 31, Page B10

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