The wild is home to some of the weirdest family relations in the world. If you think human concubinage, adultery, or polygamy are pathological acts that have little biological basis, read more about how they do things in the rest of the animal kingdom and you might change your mind.
One of the most common things you’ve probably heard about is the taking over by one male of another’s family/group. The most common examples of this behaviour are the takeovers done between male lions and even between meek and mild dolphins. This, however, is as biologically natural as hunting for food. To eliminate rival DNA and propagate one’s own is an “evolutionarily stable strategy,” as zoologist Richard Dawkins put it.
There’s more to it than that, however, since there are times when the male who takes over actually rears the offspring of the previous male as his own. Now, why would anyone do that? As of now, this is yet a scientific anomaly that biologists are trying to understand, but there have already been numerous theories put forth out there to start the discussion.
One theory is that the species that do exhibit this behaviour observe polyandry. To the layman, this means females get in the sack with several other males who can’t be sure which offspring belong to which father. With this lingering crisis, the male has no choice but to distribute his paternal care to as many offspring as he can in order to cater to the slim chances of him nurturing his actual inheritor.
“If there is some chance the infant might be his, it's worth protecting and helping to raise that family,” says David C. Geary, an evolutionary psychologist at the University of Missouri.
Sometimes, there’s a trade-off involved. Animals, like baboons, take care of offspring not of their own genes in order to impress the female they're trying to mate with. The tacit agreement is that, “If you protect my kid, I’ll let you have one of your own.” Most baboons apparently think this to be a good deal, since scientists observe them even fighting off other males who physically harass their innocent adopted offspring.
Generally, though, being a friendly male looks good in front of the females since this usually signals reliability in other matters that have to do with survival in the wild and helping members of the family get out alive from the toughest conditions Mother Nature can bring. Geary says you can even consider this behaviour to be networking, if you’re that convinced.