The Descent of Man is a much more daring book than The Origin of Species, yet Browne downplays its radicalism, presenting it largely as an endorsement of the Victorian status quo. And so for Browne, Darwin "believed that biology supported the marriage bond," and "although he rejected the outward trappings of the established Anglican religion, he subscribed wholeheartedly to its underlying values and the presumed onward march of civilization." Again, "the 'higher' values were, for him, self-evidently the values of his own class and nation." Although Browne doesn't praise Darwin's purported use of biology to reinforce conventional mores and gender roles, today many on the Right do. Browne's reading explains (albeit unintentionally) why these modern conservatives find Darwin so attractive. Longing for a way to defend traditional mores, they are entranced to learn that Darwinism may supply a biological basis for them.
Unfortunately, Browne's reading doesn't do justice to Darwin's full argument. While it's perfectly true that in The Descent of Man Darwin claims that some traditional virtues are sanctioned by nature, he also shows that a great many traditional vices are grounded there as well. Kindness may be natural according to Darwin, but so is cruelty and lust. Maternal instinct is natural, but so is infanticide. Monogamy is natural, but much more so is polygamy. Courage is natural, but so is cowardice. Care toward family members is natural, but so is euthanasia of the feeble, even if they happen to be one's parents (here Darwin mentions the practice some primitives have of burying their sick parents alive). If Darwin provides some examples of virtue in nature, he also presents nature's shocking immoralities.
What eventually becomes clear in The Descent of Man is that Darwin's view of nature points not to Aristotle or Aquinas, but to Thomas Hobbes. Nature may on occasion sanction certain traditional virtues, not because these virtues are intrinsically good, but only because at the moment they happen to promote biological survival. If circumstances should change, and these virtues no longer promoted survival, then for Darwin they would cease to be virtues. In the end, the only permanent and unchanging moral imperative is the drive for self-preservation.