These results do not square with expert predictions_其他

These results do not square with expert predictions

Animal behaviorists have been trying to understand the motivation behind altruism for decades, with little success. Some suggest that acts of kindness do not square with our Darwinian view of natural selection. Others argue that animals are simply compassionate creatures, willing to help others even while incurring a cost to themselves.

Darwin’s law of natural selection, however, states that only the individuals who are most fit for their environment pass on their genes to the next generation. The “evolutionary game” is to increase copies of your genes at the expense of those of other individuals.

Adoption, then, does not seem to make sense under this law: By adopting another female’s offspring, you are passing on her genes instead of your own. In addition, you might be putting your own offspring at risk by having one more mouth to feed. Why, then, would a female choose to raise another female’s offspring?

My own research on North American red squirrels, a species known to be non-social, has shown that adoption can indeed be explained by Darwinian evolution. My findings challenge rather simplistic notions of animals as being either “selfish” or “altruistic.” Instead, our research suggests that selfish and selfless behaviors are often deeply, perhaps paradoxically, intertwined.

My colleagues and I have found that red squirrels do not treat all orphaned young equally. In fact, we found that red squirrels never adopt unrelated orphans but do adopt related orphans as long as they are related closely enough for the benefits of adoption to outweigh the costs. Relatives share a portion of their genes; the more closely related they are, the higher the proportion of genes shared. Adopting a relative means the surrogate female is helping to pass on the genes she has in common with her relative.