Man's Place in Nature - Comparison With The Descent of Man

Comparison With The Descent of Man

Eight years after Man's Place, Darwin's Descent of Man was published. In it Darwin faced the same task of persuading the reader of man's evolutionary heritage. He took, in Chapter 1 The evidence of the descent of man from some lower form, an approach which made good use of his vast supply of information on the natural history of mammals.

Darwin starts: "It is notorious that man is constructed on the same general type or model as other mammals..." (p6) He goes on to discuss infections by similar diseases, the similarity of non-contagious diseases compared with monkeys, the liking of monkeys for tea, coffee and alcohol. He draws a wonderful word picture of baboons grumpily holding their aching heads the day after a drinking session (p7). He was aware that closely related animals always seemed to suffer from closely related parasites. He follows Huxley in his account of man's embryonic development, and then considers the evidence of vestigial organs, which he (and Huxley) called rudiments (p11). The discussion of a rare human hereditary condition permitting its possessors to move their scalps is connected to the regular use of this ability in many monkeys. The fine lanugo, a covering of hair on the human foetus, is thought by Darwin to be a vestige of the first permanent coat of hair in those mammals which are born hairy. The existence of non-erupting third molars is connected to the shortening of the jaw in humans, and, like the shortened caecum in the alimentary canal, is an adaptation to the human change of diet from full herbivory (humans are omnivores) (p20–21).

"The bearing of the three great classes of facts now given is unmistakable... are intelligible if we admit their descent from a common ancestor, together with their subsequent adaptation to diversified conditions... Thus we can understand how it has come to pass that man and all other vertebrate animals have been constructed on the same general model, why they pass through the same early stages of development, and why they retain certain rudiments in common. Consequently we ought frankly to admit their community of descent" (p25).

Later, in Chapter 6, Darwin produces his famous passage on the birthplace and antiquity of man, quoting the Chimpanzee and Gorilla as evidence that "...as these two species are now man's nearest allies, it is somewhat more probable that our early progenitors lived on the African continent than elsewhere" (p155).