EngWiPy said:
It would be helpful if you could tell us exactly what you read, as there are more than one theory about the genetic basis of human behavior, and they don't all agree about the answers to the questions you're asking.
Humans do engage in behaviors that seem to provide nothing tangible in return. When I give a panhandler a dollar I'm going to be a dollar poorer, and I get nothing back except maybe a happy twinge in the pleasure centers of my brain or suppression of unhappy twinges in worry/anxiety centers. We can interpret this observation in several different ways:
1) I want the pleasure twinge badly enough to spend a dollar on it, and I wouldn't give the dollar otherwise; therefore my behavior is best interpreted as selfish and self-interested, not altruistic. Do note that the premise before the semicolon cannot be tested experimentally so what comes after the semicolon is an assertion, not an observationally supported scientific conclusion.
2) I gave a dollar away out of the goodness of my heart; obviously that behavior is altruistic and I'm a nice person (or at least I'm acting like one at the moment). Follow this line of thought and you'll find that you've just moved the problem around: Others seem to approve of my altruistic behavior, but is that because they are "naturally good" people or is some sort of self-interest at work with them as in my #1?
3) I am displaying a genetically determined behavior that cannot be meaningfully characterized as "altruistic" or "selfish"; it just is, one of those things like hair color that's just along for a ride in the genome. Presumably the behavior is not terribly maladaptive or it would have been selected out; but that doesn't mean that it has to be adaptive or there "for a reason".
4) I am acting according to genes that have evolved and persisted because their benefits (forming and maintaining communities) exceed their costs (occasionally waste a dollar). From this point of view my giving away the dollar is somewhat analogous to baby monkeys hiding from a cardboard cutout of a hawk as if it were the real thing - "hide from hawk-shaped objects" isn't at a strong selective disadvantage relative to "hide from hawks".
#4 is probably closer to the modern scientific consensus than anything else, but do note that it avoids the question you asked, whether we are "naturally selfish" or "naturally nice"; and also the follow-on question of whether there is morality beyond what is genetically determined.
Google for "Wilson altruism" for more on the subject. "The Selfish Gene" by Richard Dawkins is also worth a read, as long as you read the criticisms as well.