Charles Darwin addresses the origin of mankind by evaluating whether human beings, like other species, descend from a pre-existing form. He gathers extensive evidence from human anatomy, pointing out the close correspondence between the bones, muscles, and viscera of humans and those of higher mammals and anthropoid apes. Special attention is given to rudimentary organs, such as the vermiform appendix and the os coccyx, which serve as structural vestiges of a shared evolutionary lineage.
The inquiry extends to embryological development, where Darwin demonstrates that human embryos share striking similarities with those of other vertebrates during early stages. He examines the laws of variation and inheritance, noting that humans are subject to the same variability as lower animals, driven by conditions of life, use and disuse, and reversion to ancient types. These biological principles lay the groundwork for understanding human descent from earlier, lower forms.
A central focus of the text is sexual selection, which Darwin explores at great length to account for secondary sexual characteristics that natural selection alone cannot explain. He details the principles of sexual selection across the animal kingdom, tracking ornamental plumage, weapons, and vocal powers through insects, fishes, amphibians, birds, and mammals. This mechanism relies on the eagerness of males and the power of choice exerted by females, shaping traits that enhance reproductive success.
Applying sexual selection to humans, Darwin examines the physical and mental differences between the sexes and the influence of varying standards of beauty across different human races. He argues that sexual selection has played a significant role in differentiating human populations and modifying traits such as hair distribution and skin color. These dynamics operate alongside natural selection, which acts through the struggle for existence and the survival of well-adapted groups.
In comparing mental powers, Darwin asserts that no fundamental difference exists between humans and higher mammals. He details how animals share emotions, attention, memory, imagination, and rudimentary reasoning. While human intellectual and linguistic capacities are vastly superior, they represent a difference in degree rather than kind, evolving through continuous mental exercise and social interaction.
The development of the moral sense is traced through social instincts, sympathy, and the influence of community opinion. Darwin explains how social animals acquire conscience as enduring social impulses overcome transient selfish desires. The work concludes by synthesizing these threads, arguing that humanity's exalted position is the result of natural and sexual selection operating over vast epochs of time.
