Charles Darwin scarcely mentioned the evolution of humanity in his most famed treatise On the Origin of Species. Darwin had hoped that some other competent evolutionist would trespass that taboo whenever the time was right. The naturalist realized in his increasingly fragile age that he would have to be the one to justify the claim that humanity had evolved from non-human animals. While vindicating this claim, Darwin unpacked a load of evidence in his volume The Descent of Man. In light of this treatise, the following summarizes some of the evidence Darwin purported that gave credence to the view that humanity had evolved from other animals.

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In chapter one of The Descent of Man, Darwin makes note of the similarities between the human skeleton and the skeleton of other mammals. For example, the bones of the bat’s flying wing and the human wrist are homologous. Darwin speculated that the two species had branched from a common ancestor. The same relationship held true for monkeys and the zeal. In order to drive his point further, Darwin flushed out even more similarities between man and monkeys. Monkeys, for example, are susceptible to the same diseases that plague humanity, including apoplexy and inflammation of the bowels. He even recounts social customs shared between monkeys and humans As Darwin highlights, “Many kinds of monkeys have a strong taste for tea, coffee, and spirituous liquors: they will also, as I myself have seen, smoke tobacco with pleasure (Darwin, The Descent p.6).” Here, Darwin is illustrating that there is not a strict dividing line between the monkeys and humans. In addition, Darwin highlighted superfluous animal features humanity shares, including excessive hair, eye brows and wisdom teeth.

In the second chapter, Darwin proposes that the processes that dictate natural selection are manifest in the human population. Darwin makes reference to the diversity of the human race as illustrated in the following:
‘No two individuals of the same race are quite alike. We may compare millions of faces, and each will be distinct. There is an equally great amount of diversity in the proportions and dimensions of the various parts of the body; the length of the legs being one of the most variable points (Darwin, The Descent, p. 20).’
He acknowledges that human variation is due to environmental pressures; however, Darwin suggests that there are internal factors at play as well. In addition, Darwin makes note of the mental differences between men of other races. Intelligence comes in different degrees. In continuation of mental powers, Darwin sites that baboons are remarkably intelligent creatures. Therefore, there are no dividing lines between animals that are intelligent versus those that are not intelligent. Rather, intelligence is a continuum marked by varying degrees. Due to the transparency of certain biological and mental capacities, Darwin argues that the kinship between the human race and monkeys is quite real.

Chapter three focuses on how mental powers could have evolved from lesser mental powers. Darwin emphasizes that there is no dividing line between man’s mental powers and the mental powers of other animals. Darwin begins by noting that human and non-human animals share many of the same instincts. These include self-preservation, sexual love and filial love. Furthermore, animals enjoy excitement and have a natural curiosity about the world. Even our sense of beauty is not unique to us, Darwin argues, since some male birds appear to exhibit an appreciation for beauty when singing. So why should it not be the case with respect to man’s intelligence?

Darwin then proceeds to focus on how language and intelligence could have evolved from primitive instincts. As Darwin conjectures:
‘The fewness and the comparative simplicity of the instincts in the higher animals are remarkable in contrast with those of the lower animals. Cuvier maintained that instinct and intelligence stand in an inverse ratio to each other; and some have thought that the intellectual faculties of the higher animals have been gradually developed from their instincts (Darwin, The Descent, p. 52).
For example, although dogs cannot speak language, they are capable of comprehending certain aspects of human language. Furthermore, Darwin illustrates that monkeys are capable of using a lesser form of language by communicating and responding to various howls and cries. Darwin highlights the primitive instincts of animals in order to illustrate how complex intelligence could evolve from simple precursors.

The Descent of Man is a magnificent bound collection of vignettes that makes it increasingly difficult to deny the human race’s kinship with the rest of the biological kingdom. Contrary to Darwin’s hesitations, many people had already figured out from The Origins that the principles of natural selection must transpire to humans as well. Nevertheless, the book served a lamppost to, as Darwin felicitously remarked, “throw light on man’s origins.”