Shenvi claims that "it is incredibly hard to envision a scenario in which it is genetically advantageous to... adopt and raise children of another race." I disagree.
Children can be a source of cheap labor. For a struggling farmer, adopting a child or two, no matter their race, can be advantageous to the farmer, his wife, the children themselves, and perhaps even their community - if the farmer can produce enough to sell at a good price to his neighbors.
Adopting children is not always advantageous, however, as in the times when they become too burdensome and not help out on the farm. There are situations when adopting children would be beneficial, and when it would not. But the fact that it would sometimes be beneficial, however, is enough for the human desire to adopt children to persist through time and not be "weeded out of the human population by natural selection eons ago" as Shenvi would expect.
If there are other behaviors that may not be explained evolutionarily, I'd like to know about them.
Keep in mind, I'm not arguing evolution can tell us what is moral. Rather, I'm arguing there are better explanations for Shenvi's evidence. I'm explaining Shenvi's evidence without invoking objective morality.