If you accept the argument in Descent of Man, you accept a racist argument
In Darwin's day, "polygenists" believed that the races had separate origins, and "monogenists" believed that we all have the same origins. Monogeny is, for example, the view advanced in the Biblical story of Adam and Eve. Darwin didn't believe Adam and Even had existed, but he did believe that we evolved from a common ancester with apes.
However, the notion that therefore Darwin wasn't a racist is completely unfounded (go here for racist statements in his Descent of Man. ). Flannery writes, "In fact, it could easily be argued Darwin cleared out the polygenists to give way to a new generation of racial discriminators and engineers." Precisely.
Quite honestly, I find current Darwinist efforts to get the old Brit toff off the hook for racism embarrassing. Far from differing from his generation's racist beliefs, Darwin wanted to provide solid scientific support for them. And to the extent that anyone accepts the argument in Descent of Man, they accept a racist argument.
Has anyone noticed how Darwinists carefully protect themselves from having the issue framed bluntly in those terms?
Part of their technique is to confuse racism with support for slavery. Many racists have opposed slavery, as Darwin did. As a social institution, slavery creates many evils. For example, young men can force slave women to have sex with them, and produce children that they do not regard - and are not expected to regard - with paternal care.
That, by the way, as British sociologist Hilary Rose has pointed out, makes nonsense of Dawkins's claims about selfish genes. Much misrepresentation in this area depends on people simply not knowing or not noticing certain well-established facts about human nature, because the institutions that reveal them - slavery, for example - are no longer current in their part of the world.
Incidentally, recognition (or otherwise) of fatherhood does not depend on race. Russian aristocrats ignored their children by serf women who were of the same race as themselves.
Lastly, while slavery was a race-based institution in the Southern States, in other times and places, slaves and serfs have often been of the same ethnic group as their masters. The link between slavery and racism - forged naturally in our minds because of that history - is incidental. It is also very convenient to those who would airbrush Darwin's racism by pointing to his opposition to slavery.
The question is, why do they need to do this. Why can't they just admit it and move on?
One reason might be that they do in fact accept the argument in Descent of Man, which means that ...