Charles Darwin was never one to understate his case. The Descent of Man is a 900-page barrage of evidence and argument, making the case that our own species, just like every other species on our planet, evolved from earlier species. Nobody capable of assessing the evidence now doubts this to be the case, but in 1871 such a view was still controversial with a sizeable portion of the general public, and with the more dyed-in-the-wool scientific establishment.
Famously, Darwin tactfully (and tactically) avoided treating the subject of human evolution in his most famous book, On the Origin of Species, limiting himself to the coy observation that ‘Light will be thrown on the origin of man and his history.’ In The Decent of Man, Darwin finally sets out to enlighten us on our origins.
Surprisingly, most of The Descent of Man does not directly address human evolution. Instead, Darwin discusses at length his second major theory of evolution: sexual selection. Nowadays, we tend to think of sexual selection as a special sub-set of his more famous theory, natural selection. But Darwin was careful to keep the two separate: while natural selection concerned the differential survival of individuals, sexual selection concerned their differential success at finding, attracting, and keeping hold of mates.
The evidence Darwin presents concerning sexual selection is vast. He systematically describes all manner of secondary sexual characteristics: adaptations evolved to help individuals breed successfully. Such characteristics include features to attract potential mates (alluring songs, sounds, smells, colours, ornaments, etc.), and features to deter or fight would-be sexual competitors (horns and antlers, protective armour, increased body size, and so on). Having been amassing evidence for decades, Darwin brain-dumps on us, presenting example after example of secondary sexual characteristics from throughout the Animal Kingdom. After the first couple of hundred pages, you find yourself waving a metaphorical white flag: OK, Charles, I get it: you’ve convinced me!
Either side of his huge thesis on sexual selection, Darwin discusses human evolution. At times, some of the language he uses is uncomfortable for modern readers. Like almost every other educated Westerner of his day, Darwin was in no doubt that white Europeans were superior to all other ‘races’ of human beings, and that the men of all races were generally more intelligent than the women. But in a number of places, he is careful to point out that he is judging other races by his own culture’s standards, not theirs. Likewise, we should not judge the upright Victorian Charles Darwin’s politically incorrect language by our own twenty-first-century standards. Darwin was a well-meaning man, who believed all human races were closely related and belonged to the same single species, Homo sapiens—a recognition not shared by certain less liberal scientists of his day.
After a relatively brief discussion of the ‘rudimentary’ human organs that provide clues to our ancestry, Darwin turns to the subjects of intelligence, morality, and civilised habits, arguing how something like their precursors is reflected in many other living species. While these topics clearly needed to be addressed, by their very nature they do not leave any physical evidence, so Darwin is forced to make conjectures of varying degrees of plausibility.
Darwin is on much firmer and more comfortable ground when he turns to the subject of our species’ genealogical descent, and our relatedness to other living species. Here, he takes us back in time, describing our increasingly remote common ancestry with apes, other mammals, reptiles, amphibians, and ultimately fish. This chapter (chapter VI) is Darwin at his most compelling. He concludes it with a wonderful passage that had me punching the air in agreement:
Thus we have given to man a pedigree of prodigious length, but not, it may be said, of noble quality. The world, it has often been remarked, appears as if it had long been preparing for the advent of man; and this, in one sense is strictly true, for he owes his birth to a long line of progenitors. If any single link in this chain had never existed, man would not have been exactly what he now is. Unless we wilfully close our eyes, we may, with our present knowledge, approximately recognise our parentage; nor need we feel ashamed of it. The most humble organism is something much higher than the inorganic dust under our feet; and no one with an unbiassed mind can study any living creature, however humble, without being struck with enthusiasm at its marvellous structure and properties.
As the above quotation demonstrates, Darwin writes with considerably more confidence in The Descent of Man than he did in On the Origin of Species. He treats evolution by means of natural selection as a given: a theory that has won the day, and need not be couched in conditionals, subjunctives, and double-negatives. I like this more confident Darwin. Strut your stuff, Charles!
Darwin returns to human evolution after his major detour into the subject of sexual selection. It is now that we finally begin to appreciate the relevance of the detour. Darwin needed to get us on board with sexual selection before he can use it to describe secondary sexual characteristics in humans. A large number of human characteristics, he argues, might well result from human sexual selection. It would seem to explain why men are generally larger (and, he would have us believe, more intelligent!) than women. It might also explain the differing standards of beauty and courtship rituals across different peoples. Ultimately it might even explain different skin colours and body-hair patterns across the ‘races’. As a proud beardy, I was delighted to hear I might owe my abundant facial hair to a long line of European female predecessors who found that sort of thing indescribably sexy—a trait that, sadly, seems to have died out in their less discerning female descendants.
The Descent of Man, and Selection in Relation to Sex is a colossal and daunting read, but it contains some wonderful observations, and plenty of food for thought, albeit some of the language used is uncomfortable to modern ears.
A really-ought-to-read for all my fellow Darwin groupies.