As an atheist, I don't have any problem in stating the evolution has caused humans not to kill members of their group, usually a tribe comprising no more than about 150 individuals, for genetic reasons, based on variations in frequencies of unknown but potentially knowable variants of genes.We know very little about the group dynamics of prehistoric man- that's what "prehistoric" means. The extent to which human behavior is genetic is hotly debated, and it's unclear how much of a role cultural learning vs natural selection played. I'm unaware of genes that cause or prevent in-group killing.
And all scientific speculation involves "unknown but potentially knowable" entities. Not much science and less logic there, and pretty thin gruel on which to base an understanding of moral law. Nice story, though.
Humans without this genetic aversion to intragroup murder would cause the destruction of the group. Everyone outside the group being regarded as 'fair game'.Actually, throughout human history there have been lots of cultures in which in-group killing is common and even integral to the social structure. Patriarchal polygamous societies intriniscally tend to this: if the alpha male has 10 wives, nine guys do without. Gets pretty violent. One might say that in-group and out-group killing has characterized many human societies.
Of course, you can explain this as evolution- the alpha male spreading his genes. Evolution explains nothing, because it can explain anything.
With civilization, the idea of the size of the group has progressively increased, hopefully to include the entire human population for most individuals.There are countless millions of people who would like to kill you. And me. Some human societies are less violent than in the past, some are more violent. Take a walk at midnight in bad neighborhoods of Baltimore or Chicago, or go to Mecca, touch the Kabba, and then announce that you're an infidel, and you'll get up to date on recent trends in violence.
I can well imagine that if civilization broke down, perhaps due to a global environmental disaster such as a global nuclear war, the size of the group inside which murder was discouraged would rapidly drop back to 150 or less, and it wouldn't matter whether they were theists or atheists, once it becomes a matter of survivalMaybe. There have been any number of disasters- wars, famines, natural disasters- in which your theory can be tested now. What's the data? Evolutionary stories are charming.
You still didn't address my point in my post on atheism and moral law:
Do you really believe that murder isn't wrong objectively and intrinsically, independent of evolution or of our opinions?