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Sexual adaptations: Compiling the evidence and how it relates to human evolution,
This review is from: The Descent of Man (Penguin Classics) (Paperback)
It wasn't until a few years after the publication of The Origin of Species (1859) that natural selection completely overhauled biology as the unification principle widely sought after to explain uniformity and diversity in living things, Darwin had himself uncovered a type of natural selection, sexual selection, mentioned it briefly in Origin but held back on explaining it fully because it would require more work to do so. The result was the 2 volume The Descent of Man, and Selection in Relation to Sex published in 1871 that spanned nearly 700 pages. Here both volumes are presented in one.
Darwin and Wallace had co-discovered natural selection as the main mechanism of evolution. Wallace however had succumbed to supernatural explanations and had largely refused to accept that sexual selection could produce some adaptations. Maybe this was because he thought that some adaptations could be explained another way but Darwin had compiled enough evidence to suggest that sexual selection was responsible for many adaptations and was also thusly more evidence for his theory of natural selection. There was only one way to do this and that was to set about documenting as much as Darwin could on sexually selective traits. It is a mammoth undertaking and is primarily the book that got the ball rolling on explaining these adaptations.
As someone who has read this book I am surprised by how it is often wrongly misrepresented by creationists as a work of unabashed racism. Out of the 700 pages I found maybe a few lines that would today require some more elaboration to make the intention clear. That is for today, nearly 140 years since it was written and only 50 years after western civilization had abandoned segregation. Darwin's work is nothing short of 140 years ahead of its time during an era that was still working to abolish slavery. Still we are always going to have some individuals who do not understand this context (maybe deliberately) so reasons are given by way of a 21st century introduction (James Moore and Adrian Desmond in my edition). There is no excuse for the detractors to be ignorant about this matter, an issue that only appears in possibly several lines out of the hundreds of thousands that are here. So let's be done with that and move on to the science.
Darwin sets out by indicating homologous structures among organisms classed as different species. During correlation he also introduces vestiges as evidence of our origins. He then turns to mental powers and instinct, especially between humans and other primates, their ability to reason and use tools and awareness. Darwin directly implies that god belief could stem from evolution as does morality. He talks about social structures, especially with insects. He analyzes indigenous peoples (called savages back then) as evidence for descent and compares developments through variations, inheritance and their causes. The important point here is that the ultimate causes are the same for all living things including humans. Darwin looks at parts that we use and do not use, gives reasons for them, treats the topic of erect walking, canine teeth, skull shape, nakedness, our tail bone, brain expansion, our ranking in the animal kingdom, the various races and their extinctions.
Darwin then turns to sexual selection as an explanation for a variety of adaptations. He looks at polygamy, variability, proportions of males to females and the question surrounding this. Turning to the animal kingdom he looks closely at colours, dimorphism, structures for holding during mating, musical instruments (stridulating), pugnacity, adaptations for sexual conflict, courting, colour protection and differences in colour between males and females and mimicry. He covers all of these with birds, fishes, amphibians, reptiles, insects and mammals.
He expands on them in advanced chapters such as on the topics of building nests, parental care, laws of battle, dancing, seasonal variations, moults, female choice, exceptions to these observations, sex-limited traits, male and female role reversals, absence of weapons in females, weapons with both sexes, vocals, odours, hair, skin colour, spots and stripes.
Now that Darwin has firmly established sexual selection he then turns to humans, the differences between the sexes, commonalities, law of battle, mental powers, voice, beauty and marriage, exaggerations, beauty standards, bodily hair, skin colour and the final conclusion that man is descended from some lower form and is self evidence of his lowly origin.
Most of the book is devoted to comparing sexual traits between varieties of organisms. There are very clear illustrations (something Origin doesn't have) every few pages. The style is very much fact upon fact upon fact. There is a huge amount of footnotes on every page with Darwin referencing everything meticulously. There are lists of birds after amphibians after mammals after fish after insects. It is a globe sprawling nature walk. We are talking hundreds of pages on observed facts. Darwin even discusses behaviour in relation to animal signalling.
His description of sexual selection among organisms vastly outweighs the actual topic of the descent of man and makes it almost seem redundant but the purpose is clear. Once Darwin has established sexual selection with other organisms and shows how the adaptations appear he then applies the same criteria to humans and abruptly we emerge from the picture of an ape-type hominid ancestor. Sexual selection makes it all too evident why we appear the way we do. Ideas that our attributes are based on a divine representation for a sanctified existence have lost. We are shaped by our desires.