Questions for Darwin's "On the Races of Man" from The Descent of Man

What is the effect of Darwin adding the qualifier "so-called" to "races" when he opens his chapter "On the Races of Man" (i.e., Sentence 1: "It is not my intention here to describe the several so-called races of men")?
 

What rhetorical strategy does Darwin employ in order to present and refute counter-arguments regarding the significance of racial differences for classification purposes?
 

Because Darwin looks at both sides of the argument regarding racial difference from a seemingly objective point of view, his argument may appear impartial.  Do you think he has an opinion on the question of race as it applies or doesn't apply to humans?  If so, how does he convey it?
 

Look at Paragraph 2 on p. 41 (in the reader; p. 62 in the original text), which begins, "But the most weighty of all the arguments against treating the races of man as distinct species . . . "  What's Darwin's point in this paragraph?
 

According to Darwin, how many different races are there?
 

What is Darwin's conclusion regarding the terms "race" and "species" as they apply to humans?
 

What does Darwin mean when he says that humans are polymorphic?
 

Does he say or imply that non-white races are inferior?  Where?
 

How might we reconcile his apparently racist language and/or statements with other his apparently anti-racist language and/or arguments?
 

What's his overall thesis in this chapter?
 

In paragraph two of the excerpt from The Voyage of the Beagle, note that Darwin moves from a general indictment of slavery to a direct challenge to his readers to sympathize and identify with slavery’s victims.  What response does this aim to elicit from the predominantly Anglo audience?