I think psychological experiments have pretty well concluded that there isn't any essential "human nature."
Some people are always altrustic and honest, some people are rotten to the core and always will be, and others are somewhere in the middle.
Whether they got that way by "nature" or "nuture" or some combination is hard to say. Maybe some of the rotten ones became that way due to poor environment in childhood, and maybe some just came that way from the factory. For my part think a lot of altruistim is probably learned/cultural and not innate. But it's likely that any human population can sustain a small number of sociopaths that prey on the rest of the population as an "evolutionary stable strategy." It's probably why high-conflict people are sometimes called "emotional vampires."
The whole "evolution" vs. "culture" thing is sort of a chimera anyway; we've had culture for by some estimates 2 million years. They're starting to become inseparable.