Animal adoptions make no evolutionary sense, so why do they happen?
Scientists used to think that humans are special because we have larger brains than other animals. However, some experts in human evolution have suggested that it isn’t how we think that makes the difference, but how we feel. They suggest that humans may have evolved to be kinder to one another, or at least to suppress their tendency to lash out in anger.
Dominant males sometimes try to “guard” the female from competitors to ensure that she mates exclusively with him. In these cases, individuals only know their maternal kin: mother, siblings and perhaps aunts and cousins. Within a social group, a male has no way to know which babies might be his, so will generally be tolerant – but he might commit infanticide when he takes over a new group and knows they definitely are not his children.
Infanticide by a newly dominant male can also be explained by the fact that milk production acts as a natural contraceptive. So when a female stop nursing, she becomes fertile again. This makes her available to bear the new dominant male’s offspring much sooner than if she were to wait until her existing baby is weaned.
Humans are not so unique after all
We would argue, however, that the adoptions described above by gorillas, bonobos and dolphins don’t fit any of these models. Perhaps humans are not unique in their capacity for generosity after all?
After all, animal behaviour specialists have suggested that spontaneous generosity is actually well-known and it is well documented among other large-brained, highly-social animals, such as apes, dolphins and elephants. In addition to adoptions, chimpanzees routinely comfort the loser of a fight. They are also occasionally known to commit heroic acts of selflessness, like dying to rescue an infant from drowning.
Attempts have been made to look for “hidden” relationships between helper and recipient, to make altruism “fit” with evolutionary selfishness. Perhaps instead we may just have to accept that humans are not unique in their capacity to care for and help each other.