Not to turn on the religion-rant button again, but The New York Times had an interesting review of a book that argues that a basic sense of right and wrong are hard-wired into humans, much as Noam Chomsky argues that the the capacity for language is also part of our innate neural machinery. To quote the Times article: This "moral grammar... is a system for generating moral behavior and not a list of specific rules. It constrains human behavior so tightly that many rules are in fact the same or very similar in every society — do as you would be done by; care for children and the weak; don’t kill; avoid adultery and incest; don’t cheat, steal or lie. But it also allows for variations, since cultures can assign different weights to the elements of the grammar’s calculations."
The book then "suggests that religions are not the source of moral codes but, rather, social enforcers of instinctive moral behavior." Told ya so! you can be a good person (in fact, you're somehow neurally deficient if you're not) without the dogma and trappings of organized religion.
At the dawn of the species, the argument goes, evolution favored groups of people whose members helped each other survive and reproduce, hence the moral grammar. Of course there are still plenty of "bad" genes in the human genome that hinder successful reproduction (cystic fibrosis, etc.) but they're rare in terms of the whole human population, so the species isn't threatened by these genes. You could make a case that people who for some reason lack this "moral grammar" gene ARE in fact a threat to the species, given the technology for killing that we've evolved. Recent conscienceless psychopaths have been responsible for killing a large number of people (even millions); will there come a time when a combiniation of technology and a few people without moral grammar could in fact wipe out the whole lot of us? Only the shadow knows.