As Darwin wrote, he sent chapters to his daughter Henrietta for editing to ensure that damaging inferences could not be drawn, and also took advice from his wife Emma.

From this Darwin then provides evidence for similar mental powers and characteristics in certain animals, focusing especially on apes, monkeys, and dogs for his analogies for love, cleverness, religion, kindness, and altruism.

"[5] He additionally turns to the behaviour of "savages" to show how many aspects of Victorian England's society can be seen in more primitive forms.

In particular, Darwin argues that even moral and social instincts are evolved, comparing religion in man to fetishism in "savages" and his dog's inability to tell whether a wind-blown parasol was alive or not.

Darwin notes that, as had been discussed by Alfred Russel Wallace and Galton, natural selection seemed to no longer act upon civilised communities in the way it did upon other animals: With savages, the weak in body or mind are soon eliminated; and those that survive commonly exhibit a vigorous state of health.

The surgeon may harden himself whilst performing an operation, for he knows that he is acting for the good of his patient; but if we were intentionally to neglect the weak and helpless, it could only be for a contingent benefit, with an overwhelming present evil.

[25][23] Darwin commented that the "question whether mankind consists of one or several species has of late years been much agitated by anthropologists, who are divided into two schools of monogenists and polygenists."

The latter had to "look at species either as separate creations or as in some manner distinct entities" but those accepting evolution "will feel no doubt that all the races of man are descended from a single primitive stock".

He drew on his memories of Jemmy Button and John Edmonstone to emphasise "the numerous points of mental similarity between the most distinct races of man.

"[26][27] Darwin concluded that "when the principles of evolution are generally accepted, as they surely will be before long, the dispute between the monogenists and the polygenists will die a silent and unobserved death.

Part II of the book begins with a chapter outlining the basic principles of sexual selection, followed by a detailed review of many different taxa of the kingdom Animalia which surveys various classes such as molluscs and crustaceans.

[36] She wrote of "defrauded womanhood" and her fears that "the human race, forever retarding its own advancement...could not recognize and promote a genuine, broad, and healthful equilibrium of the sexes".

[39] As recently as 2004, Griet Vandermassen, aligned with other Darwinian feminists of the 1990s and early 2000s (decade), wrote that a unifying theory of human nature should include sexual selection.

In On the Origin of Species, Darwin wrote that to use natural selection to explain something as complicated as a human eye, "with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration" might at first appear "absurd in the highest possible degree," but nevertheless, if "numerous gradations from a perfect and complex eye to one very imperfect and simple, each grade being useful to its possessor, can be shown to exist", then it seemed quite possible to account for within his theory.

Writing to colleague Asa Gray in 1860, Darwin commented that he remembered well a "time when the thought of the eye made me cold all over, but I have got over this stage of the complaint, & now small trifling particulars of structure often make me very uncomfortable.

[43] Darwin had developed his ideas about sexual selection for this reason since at least the 1850s, and had originally intended to include a long section on the theory in his large, unpublished book on species.

When it came to writing Origin (his "abstract" of the larger book), though, he did not feel he had sufficient space to engage in sexual selection to any strong degree, and included only three paragraphs devoted to the subject.

Coming out so late into that particular debate, while it was clearly Darwin's intent to weigh in on this question, his goal was to approach it through a specific theoretical lens (sexual selection), which other commentators at the period had not discussed, and consider the evolution of morality and religion.

The theory of sexual selection was also needed to counter the argument that beauty with no obvious utility, such as exotic birds' plumage, proved divine design, which had been put strongly by the Duke of Argyll in his book The Reign of Law (1868).

[45][page needed][46] Darwin also was perplexed by the "savage races" he saw in South America at Tierra del Fuego, which he saw as evidence of man's more primitive state of civilisation.

During his years in London, his private notebooks were riddled with speculations and thoughts on the nature of the human races, many decades before he published Origin and Descent.

But while Spencer did first introduce the phrase "survival of the fittest" in 1864, he always vigorously denied this interpretation of his works, arguing that the natural course of social evolution is toward greater altruism, and that the good done by charity and giving aid to the less fortunate, so long as done without coercion and in such a way as to foster independence rather than dependence, outweighs any harm done by saving the less fit.

In any case, Spencer was primarily a Lamarckian evolutionist; hence, fitness could be acquired in a single generation and thus in no way did "survival of the fittest" as a tenet of Darwinian evolution predate it.

Neither Galton nor Darwin, though, advocated any eugenic policies such as those undertaken in the early 20th century, as government coercion of any form was very much against their political opinions.

This has been questioned by later scholars as quite a stretch for Wallace, who in this particular instance abandoned his normally strict "adaptationist" agenda in asserting that the highly intricate and developed forms such as a peacock's tail resulted by sheer "physiological processes" that were somehow not at all subjected to adaptation.

[47] Joseph Jordania suggested that in explaining such human morphological and behavioural characteristics as singing, dancing, body painting, wearing of clothes, Darwin (and proponents of sexual selection) neglected another important evolutionary force, intimidation of predators and competitors with the ritualised forms of warning display.

Adeline Loyau and her colleagues responded to Takahashi's study by voicing concern that alternative explanations for these results had been overlooked and that these might be essential for the understanding of the complexity of mate choice.

In an anonymous Quarterly Review article, he claimed that the Descent of Man would unsettle "our half educated classes" and talked of people doing as they pleased, breaking laws and customs.

As 1872 began, Mivart politely inflamed the argument again, writing "wishing you very sincerely a happy new year" while wanting a disclaimer of the "fundamental intellectual errors" in the Descent of Man.