The Accidental Species: Misunderstandings of Human Evolution

by Henry Gee

  The practical aspect of nature philosophy came with nature philosophers’ approach to the problem of generation. The problem of generation was working out how a seemingly unformed germ (such as a seed or egg) evolved into a complex, adult creature. Where did all that complexity come from?

  Some scholars thought that it appeared out of nothing, whereas others, the so-called preformationists, thought that the adult form was there all the time, just in some occult, condensed form, waiting for the right cue to unravel. The problem was that investigating the subject directly proved impossible, and by the end of the eighteenth century the subject had reached an impasse. The problem couldn’t be solved until the adoption of the cell theory, in the 1840s, and with that, the invention (one is tempted to say “evolution”) of staining techniques whereby translucent, filmy cells could be made visible under a microscope. Only then was it realized that new organisms arise from the fusion of male and female sex cells (sperm and eggs) followed by a complex series of elaborations (“evolutions”).

  In the meantime, though, the nature philosophers took the view, possibly informed by their somewhat mystical outlook, that the earliest stages of generation might be forever hidden from view, impossible to discover even in principle. If this sounds familiar, it should—astrophysicists have adopted the same view about the birth and very earliest moments of the universe, ruled by physics beyond current theory to explain, and probably beyond any capacity of experiment or observation to penetrate. But that doesn’t stop astrophysicists observing and theorizing about the history of the universe after that mystical instant of birth, and nature philosophers took the same view of generation. If the earliest moments of generation could not be seen, there was still a wealth of information to be gained about embryos, and how they grew and developed.

  When German-speaking embryologists such as Karl Ernst von Baer and especially Ernst Haeckel, who had been drenched in the culture of nature philosophy, came to look at the embryology of various creatures, they found that the stages through which a developing organism “evolves” reflects its station in the grand ordering of Creation. Creatures start from single cells, much like blobs of protoplasm. They then form into balls of cells, similar to lowly algae or sponges, which fold into cup shapes, blind sacs with an opening at one end—much like simple polyps. They then elongate, coming to look like lowly worms, with yet further evolutions demarcating successively higher states. The necks of human embryos, for example, show rudiments of the gill slits that perforate the throats of fishes. They have tails, which are reabsorbed, and just before birth, some babies are quite furry. The elision, therefore, became obvious. The great tree of life, the great chain of being—whatever one wants to call it—maps the evolution of every individual creature as it develops. To put it another way, the evolution of any creature goes through a number of stages, the last one of which determines its place on the tree of life. The canonical summary of this idea is “ontogeny recapitulates phylogeny.” This concept was meat and drink to the nature philosophers, who could now see the archetypal ideas of creatures on the grandest scales played out everywhere in the dramas of individual development. As one nature philosopher put it: “What is the animal kingdom other than an anatomized man, the macrocosm of the microcosm?”9 It was the nature philosophers then, who, when they became embryologists, made the explicit connection between what might otherwise have been seen as two quite distinct processes—evolution and transformation. Partly for this reason, one can lay the blame for today’s muddled thinking about evolution at the door of the nature philosophers and their inheritors, especially Haeckel.

  The nature philosophers did not see the natural world in terms of actual transformation, only as the expression of cosmic or divine ideals. Haeckel, though, became a firm adherent of Darwin’s evolution, doing much to popularize it. Haeckel missed the essential metaphor of Darwin’s tangled bank, however, and saw natural selection instead as a kind of motor that would drive transformation from one preordained station on the ladder of life to the next. This is the view of natural selection—as another word for the cosmic urges of nature philosophers—that some scientists10 found exceptionable toward the end of the nineteenth century, leading to Darwinism’s eclipse, yet is the view that has become ingrained in the public mind whenever the word “evolution” is mentioned. It is this Haeckelian bastardization of natural selection that’s responsible for the arrows in figure 2, the engine that drives evolution forward, from simplicity to complexity, in a series of Ciceronian maneuvers with a definite beginning and a culmination in Man—as far from the undirected, contingent, and moment-by-moment actions of natural selection on the tangled bank as might be imagined.

  And if we think that this piebald view of evolution, as forever progressive and improving, striving ever toward the transcendent light, is something espoused only by misinformed journalists and newspaper readers who know no better, we must think again. When I was an undergraduate, back in the mists of time (okay, it was 1981), my zoology textbook was the very latest edition of The Life of Vertebrates, by the influential, immensely respected, and very sensible zoologist, the late John Zachary Young. Here is Young summarizing the evolution of mammals, the group of creatures to which we ourselves belong.

  We shall expect to find in the mammals even more devices for correcting the possible effects of external change than are found in other groups. Besides means for regulating such features as those mentioned above we shall find that the receptors are especially sensitive and the motor mechanisms able to produce remarkable adjustments of the environment to suit the organism, culminating in man with his astonishing perception of the “World” around him and his powers of altering the whole fabric of the surface of large parts of the earth to suit his needs.11

  Yes, you read that correctly—Young really does use the phrase “culminating in man.” And if that’s in a modern undergraduate textbook, written by an acknowledged authority, it is little wonder that people more generally find it hard to grasp what evolution (in the sense of descent with modification) is all about.

  We can’t put all the blame at Haeckel’s door, however. When the Origin first erupted (there is no other word) into the public consciousness, commentators were less worried about the niceties of natural selection, still less that Darwin could not explain the mechanism of inheritance on which his theory depended, but about the challenge that Darwin’s ideas made to established social orthodoxy. In place of a static social order, a possibility of change—of liberation, progression, advancement, improvement. What we would now call a left-wing thinker such as Harriet Martineau (who knew Darwin personally) and particularly Herbert Spencer (who coined the phrase “survival of the fittest”) co-opted Darwinian evolution in support of a general theory of social evolution that had all the hallmarks of the directed, progressive strivings that one would see turning up everywhere from manifest destiny and Marxism to fascism and advertising.

  The OED defines sense 10 of “evolution” as “progression from simple to complex forms, conceived as a universal principle of development, either in the natural world or in human societies and cultures” and cites Martineau.

  It was Spencer, not Haeckel, who championed evolution among what we might now call the “chattering classes,” in opposition to the nobility and the established church, and who wrote, just before the Origin was published, that “those who cavalierly reject the Theory of Evolution, as not adequately supported by the facts, seem quite to forget that their own theory is supported by no facts at all.” The battle lines were drawn between the agents of political progress, marching forward with evolution as a kind of justification for social improvement, and the established orthodoxy to which evolution was seen as a threat. One sees the same lines drawn to this day, especially in the United States. It’s a pity that somewhere along the line, the exquisite beauty and infinite subtlety of natural selection as a mechanism has been lost, trampled into the dust by the simplistic slogans of those who’d use evolution as a device to further t
heir own ends.

  The accretion of all this social, political, and philosophical baggage over the past century and a half has tended to dull any appreciation of the disarming simplicity and beauty of natural selection as a mechanism. All other schemes of transformation current in Darwin’s day required strange and mysterious ingredients, such as Lamarck’s besoin, or cosmic strivings for betterment favored by the nature philosophers—none of which could be seen or touched, and whose existence had to be taken on trust. Natural selection required nothing that couldn’t be seen, touched, and appreciated by anyone.

  Natural selection is unique in another way, too, for unlike all other theories of transformation, it has no inherent direction. Darwin’s contemporaries and antecedents looked at the tree of life and invented processes to “explain” it that were directional and improving. Darwin turned this idea on its head. He came up with a simple process in which no particular direction was implied, but whose result would be the treelike pattern we see. The tree is just natural selection summed over history.

  Natural selection, therefore, does not demand what we from our human perspective think of as “improvement.” To go further, natural selection cannot be seen as evolution’s guiding hand. It has no personality, no memory, no foresight, and no end in view. To be sure, it’s easy to see that natural selection, if left to operate for long enough, will create the branching patterns of the tree of life in much the way that Darwin suspected it did. However, there is nothing in natural selection that allows you to predict any particular pattern that it might generate. This marks a crucial distinction between natural selection and earlier ideas of transformation that presupposed a ladderlike scheme with Homo sapiens at the top. In natural selection, the pattern we see was not preordained, manifest, or inevitable in any way. Stephen Jay Gould expressed this idea very well in his book Wonderful Life—if we could rerun the tape of life, we shouldn’t necessarily expect the same result every time.

  I’d like to go much further than Gould did. In a famous scientific paper, Gould and his colleague Niles Eldredge proposed that evolution would not always proceed gradually, according to the “insensible gradations” proposed by Darwin, but might in some circumstances proceed very rapidly, and in other circumstances not move at all.12 This was the “punctuated equilibrium” model of evolution, much debated ever since. But the arguments about evolution’s speed—and these arguments have been fierce and acrimonious—all rest on the assumption that there is a narrative to be uncovered, a story that might be read from analysis of the fossil record.

  However, any patterns that we see in the fossil record are reconstructed by us, after the fact. Because the fossil record is so fragmentary and imperfect (a point that Darwin grasped with his usual percipience), it is easy for us to read into it any narrative we like and assume that this narrative must be the right one. It is only natural for us to compose a story that suits our own prejudices of evolution (driven by natural selection) leading to ever greater refinement. This is, however, a profound misreading of Darwin’s ideas and reflects a failure to understand the uniqueness of natural selection as a mechanism of transformation. With natural selection, no fate is ever inevitable, unless reinforced as such by hindsight.

  The blob of protoplasm in Darwin’s proverbial “warm little pond” could have evolved into anything—or nothing. The fact that evolution took the course it did was a result of natural selection acting on it and its descendants, moment by moment, according to the environmental circumstances prevalent at each given instant. Looking back at the course of evolution from our privileged height, we naturally assume that the only course of evolution possible was the one that led to ourselves.

  This idea seems to have made insufficient impact among science communicators, members of the public, and even some scientists. In the world at large, many evolutionary transformations and adaptations are assumed to have been imbued with purpose. For example, feathers are seen as adaptations that allow birds to fly, as if flight were somehow the manifest destiny of birds. That this idea is wrong is shown by the evidence, which suggests that feathers evolved many millions of years before birds took to the air, among dinosaurs that patently would not have been able to fly. It is even possible that some dinosaurs, having evolved feathers, lost them again. This kind of backward-reasoning, in which adaptations are seen as having a purpose in some great transcendental game that lasts for millions of years, is also widely seen in schemes of human evolution that suppose, for example, that humans stood on two legs in order to free up the hands for making tools, to nurse babies, and so on.

  This style of reasoning, in which evolution is assumed to have a purpose or a goal, is naturally accompanied by an assumption of progress, very much in the pre-Darwinian style. The assumption of progression is not only a misrepresentation of evolution, but ignores most of what is actually going on.

  When we strip away the assumption that evolution is progressive, we find a different picture, both richer and stranger. Most of what seems to be going on in evolution is not the acquisition of new, improved ways of living, but their wholesale loss. This is quite at variance with the picture of evolution most people have, of a march of greater complexity and improvement—a picture that, as I hope is becoming clear, is sometimes misinformed. The concept of loss is explored in the next chapter.

  3: Losing It

  Evolution by natural selection, then, is not a noble or divine force that carries organisms on tracks of inevitable and inexorable improvement from the past to the future. Once we’ve roasted that old canard and served it up with orange sauce, we can begin to demolish as spurious the case for human exceptionalism.

  But there’s a catch—such progressive and inexorable improvement seems to have been precisely what has happened. Over the eons, living things really do seem to have become more complicated. Simple creatures consisting of single cells, such as bacteria, evolved into complicated creatures consisting of trillions of cells, such as human beings. If “improvement” can be equated with “complexity,” then there seems to have been a general trend, throughout the history of life, for complexity to increase.

  It is said that it takes just one ugly fact to destroy a beautiful hypothesis—so how fares my contention that natural selection is a consequence of several circumstances acting together only in the here and now, without having any end in view?

  There are (at least) three answers to this. The first was very well put by Stephen Jay Gould in his book Full House. Yes, complexity has increased—but how could it not? If the earliest life was simple and microscopic, the only way was up. That aside, complexity seems to have been the concern of the rather small subset of creatures that includes ourselves. Even today, most creatures are simple and single-celled, and almost all of these are bacteria. Bacteria swarm on (and in, and around) every surface in uncounted profusion. Anyone who has eaten reheated cooked rice and come down with poisoning by Bacillus cereus might be astonished to know that the symptoms of poisoning are apparent only if there are more than 100,000 bacterial cells per gram of food.1 This means that you can still swallow hordes of germs—cities, dynasties, empires of them—without even noticing, and suffer no ill effects whatsoever. Unbeknownst to our everyday selves, our skins crawl with bacteria, and bacteria in billions infest our guts.2 Were every living creature counted as an equal, the total sum of nonbacterial living creation would be utterly insignificant. Complex organisms, rather than representing a general trend toward improvement, seem to have been a somewhat esoteric diversion.

  Second, it all depends on what you mean by “complexity.” How can such a thing be measured, and can it really be equated with “improvement” in any simple way? The simplicity of bacteria is more apparent than real. Bacterial cells might look simple—they are usually spherical or sausage-shaped, and their innards seem entirely featureless—but they are supremely adaptable. Many have digestions far more robust than the most adventurous gourmand, and can live in conditions that would kill any human being (and virtuall
y anything else) instantly.3 Bacteria live in the upper atmosphere, and deep underground.4 There are bacteria that live in dumps of toxic effluent and in radioactive waste.5 There are even bacteria so tough that they can survive exposure to the hard vacuum and intense radiation of space.6 My point is that there are other ways of measuring complexity than numbers of cells, or the numbers of different types of cells in any given creature, or elaborateness of construction—in other words, according to the criterion by which we measure all things, that is, ourselves. More than 150 years after The Origin of Species was published, we are still wedded to the cosmic urgings of the nature philosophers, and accept it as axiomatic that Man is the microcosm that measures the macrocosm. In terms of chemical complexity, however, bacteria are far more complex than Man.

  The third answer is more involved than either of these two, and goes deep into the mechanics of complexity increase.

  The evolution of complexity is a hot topic in modern biology. The late John Maynard Smith, one of the finest biological minds of the past century, broke down complexity into a number of discrete steps, each of which had to be overcome before complexity could increase any further.7 These steps included (among many other things) the evolution of very simple bacterial cells into the complex cells with which we are familiar, with discrete nuclei and subcellular compartments. Science needs its visionaries, and few were more visionary than Lynn Margulis,8 who was the first to elaborate the idea that complex cells developed from simple cells working together to such an extent that they merged to become a single organism.9 This idea, once dismissed as far-out, is now very well established and can be seen in various stages of completion, even today.