Why do volunteer firefighters rush into a burning building to try to save children from some family they have never met before? Every day we afforded examples of people sacrificing their personal interests for the benefit of others.

But also, biologists usually use a definition of "altruism" that does not include close kin. Richard Dawkins was explicit about this in his 1976 book "The Selfish Gene." Helping someone you are directly related to is not considered altruism.

It's literally a skill issue. The correct way to help a drowning person is to get behind them and then hook your weaker arm around their neck & head while doing backstroke with the other. Having them on their back facing up (and out of the water) dispels the panic reflex. But this obviously requires you to be comfortable int he water and have some prior rescue training.

I think in the premodern era, you never saw strangers (not like we do). You probably had a pretty good idea who everyone was, and probably knew most people pretty well. If that's even partially true, then although nowadays you might drive past a person on the highway, if your cousin or a lifelong trusted acquaintance asked for help you'd give it. It seems that everyone you saw, esp saw injured or sick, was probably someone you've known your whole life.

You're also heavily discounting the fact that you had to live not only with yourself if you did nothing, but the shame/angst of their family who you definitely lived next door to. TFA is about taking care of "their own", not strangers.