The Accidental Species: Misunderstandings of Human Evolution (8 page)

Scholars before Darwin thus had two distinct phenomena to explain. First was evolution—sometimes called generation—in which a small and simple germ was elaborated (“evolved”) into a large and complex adult. The second was the apparent arrangement of life in a hierarchical or treelike fashion.

The analogy Darwin drew between evolution and transformation was not his own invention. Editions of William Harvey’s
Exercitationes de generatione animalium
(1651), one of the earliest works in the modern era to address the question of generation, bore engravings illustrating Zeus holding an egg from which all manner of creatures poured forth, with the legend “Ex Ovo, Omnia”—everything comes from the egg—a slogan that could be applied to generation and transformation with equal facility.

A more explicit connection between the two processes was drawn by the adherents of “nature philosophy,” a tendency popular in the late eighteenth and early nineteenth centuries, and particularly associated
with the poet, protoscientist, playwright, and all-around egghead Johann Wolfgang von Goethe. The nature philosophers were inclined to be somewhat romantic, which doesn’t always go down well among scientists, and it’s easy to make fun of them nowadays. However, they made two vital contributions to biological thought—one somewhat mystical, as one might expect; the other highly practical.

Although people saw life arranged as a tree, they also noticed that trees grow upward, from the ground; that you need a ladder to climb a tree if it is tall; and that it takes more effort getting to the upper branches than sitting on the ground. The treelike arrangement was therefore in accord with the ancient idea of the “great chain of being,” in which living creatures occupied a station in life according to their structure, the simpler ones (worms, insects, and so on) toward the bottom, the more complex ones (fishes, birds, mammals) toward the top. Human beings would—noblesse oblige—occupy the topmost rung, above the apes, but below the angels.

At first, this arrangement was simply a statement of the order of creation. There was no sense in which creatures on a lower rung could be transformed into creatures on a higher one. Some thinkers, however, began to question why the tree should be ordered in the way it was, rather than in any other way, and began to imagine processes whereby creatures might be transformed.

Perhaps the most famous exponent of transformation before Darwin was Jean Baptiste de Lamarck, who outlined a scheme in his book
Philosophie zoologique
(1809) in which creatures would be driven to transform by an inner force or
besoin
(need) in response to their environmental circumstances, and such transformations would be inherited by any offspring. Thus the canonical picture of giraffes extending their necks ever longer to reach the highest leaves, and passing the results of their exertions onto baby giraffes, which would tend to have longer necks than their parents. This idea sounds quaint today, but Lamarckism was a theory with legs.

Today we are inclined to think that after the publication of the
Origin
, Darwin’s ideas just went from strength to strength (such is our view of history as forever progressive), but this is not the case. Natural selection required that creatures provide a constant source of variation on which this selection could act. In Darwin’s time, though, no such mechanism was known. The discovery of genetics around the turn of
the twentieth century was to answer the question and so rehabilitate Darwin, but for half a century—between Darwin’s death in 1882 and the reconciliation of evolution and genetics in the late 1930s—evolution by natural selection was in eclipse: influential scientists turned away from Darwinism for want of an explanation of variation, leaving evolution as not much more than a set of just-so stories. William Bateson—the scientist who would later coin the term “genetics”—was typically scathing.
⁸
“In these discussions [of evolution] we are continually stopped by such phrases as ‘if such and such a variation then took place and was favourable,’ or, ‘we may easily suppose circumstances in which such and such a variation if it occurred might be beneficial,’ and the like . . . ‘If,’ say we with much circumlocution, ‘the course of Nature followed the lines we have suggested, then, in short, it did.’
” As a result of this Darwinian vacuum, many mainstream thinkers continued to favor Lamarckism, so much so that it formed the grounding of university-level textbooks such as E. S. Russell’s classic
Form and Function
(1916).

The nature philosophers looked at the pattern of life, but rather than Lamarckian
besoin
, a mechanism that was actually meant to cause transformation in the real world, they saw in each successively more elaborate form a more concrete manifestation of some ideal, cosmic striving toward perfection that would reach its acme in Man (with a capital
M
). Creatures in the real world were imperfect expressions of a transcendental ideal. No actual transformation was meant to have happened.

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 micro
scope. 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 scientists
¹⁰
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 their 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.