Darwin portrayed Indigenous peoples of the Americas and Australia as less than Europeans in capacity and behavior. Peoples of the African continent were consistently referred to as cognitively depauperate, less capable, and of a lower rank than other races...He went beyond simple racial rankings, offering justifications of empire and colonialism, and genocide, through "survival of the fittest...
However, some of tried to absolve Darwin of the charge of racism by pointing out that Darwin was an opponent of slavery. In fact, Darwin biographers Adrian Desmond and James Moore wrote a whole book making this argument: Darwin's Sacred Cause: How a Hatred of Slavery Shaped Darwin's View of Human Evolution. However, as Michael Flannery points out in his review of Desmond and Moore's book, "The central problem with Desmond and Moore's effort is their naive assumption that anti-slavery somehow means egalitarian and humanitarian." In reality, it was possible for someone to be both an abolitionist and a racist. To believe that slavery was wrong did not necessarily lead to the belief that whites and blacks were equal. Even the future "Great Emancipator" Abraham Lincoln said during the famous Lincoln-Douglas debates that "there is a physical difference between the white and black races which I believe will forever forbid the two races living together on terms of social and political equality" (see here for the source of this quotation)--a perspective that we would today view as racist (although it is believed Lincoln changed his racial views near the end of his life).
Does it matter that Darwin was a racist? I would answer "No" and "Yes." On the one hand, the fact that Darwin was a racist has no logical bearing on the validity of his theory of evolution. Although we tend to think otherwise, sometimes bad men have valid ideas, and sometimes good men have invalid ideas. Whether Darwin's theory of evolution is correct or not is solely dependent on the scientific evidence. I personally would argue that the scientific evidence, if carefully considered, does not support Darwin's theory. I believe this is amply proven by the writings of Michael Behe, Stephen Meyer and other Intelligent Design theorists. Others believe otherwise. Regardless, this is a question to be resolved through scientific (and maybe philosophical) debate.
On the other hand, Darwin's racism does matter in that his theory did, David Klinghoffer points out, give racism "a major boost in the 19th and 20th centuries." Klinghoffer goes on to quote science historian Michael Keas (who in turn quotes historian Richard Weikart):
The evil of racism was nothing new when Darwin and his evolutionary theory came on the scene, but according to Weikart, racist thinking, increased "by orders of magnitude" under the influence of Darwinism and evolutionary thinking and became mainstream science.
To be fair, some have tried to argue that Darwin is not responsible for the fact that some individuals used his theory to promote racist ideas. On a certain level this is true--Darwin had limited control over what others did with his theory. Nevertheless, it can still be argued that the racist views Darwin expressed lent intellectual respectability to the notion of "scientific racism," given his status as one of the great figures in modern science.
In short, the truth of Darwin's theory of evolution is not dependent upon Darwin's personal views about race, but Darwin and his theory gave intellectual legitimacy to racism.
Image of Charles Darwin from Wikimedia Commons