Social behavior is common across a broad spectrum of species. You can see this for yourself. Watch a pack of dogs or a herd of elephants for a while. As for humans, if we hadn't been social animals, we would not have survived long enough to evolve into what we are now. No,it has little to do with intelligence. Yes, it is a part of our biological makeup. And, yes, it is necessary.

Socialization in humans is the result of genetic selection; it is a survival strategy evolved most likely because of how long it takes our young to mature.
We socialize outside our familial group but, the familial group is likely the original social group, we formed social groups to assure the survival of our clans common genome.
At some point in our past we began to co-operate outside our clan likely as a survival strategy that benefited all members of the none familial group, so, I doubt bonding had a lot to do with it. Bonding likely came after we formed non-familial groups.
Victoria is correct in saying we are mentally hard wired to seek the company of others but, so are most primates.
In some ways we now behave a lot more like herd animals. I have noted that cows form bonds with non related individuals bonds that remain for the life time of the animals and have nothing to do with survival of shared genes or even rearing of young. Another words cows form friendships much as humans do.

Evolution has produced humans as social animals. Prior sub-species that were not social did not survive to pass on their genes.

We evolved as social animals, because ti was a successful survival strategy. We still have all those innate instincts of wanting to belong to a group, which is the primary why so many persons are religious. Most religious persons have doubts, but their need to belong is stronger than their sense of reason and rationality.