That every human society has murders may be explained by the theory of evolution, that somehow committing murder provided the perpetrators (or their siblings) an advantage in natural selection advantage, and so murderous behavior, somehow imprinted in our genes (how is never explained), got propagated through the generations.
Even if we accept that genes determine murderous behavior, that possession of such genes could be natural selection-neutral or even negative, but not negative enough to ever go extinct, is not given an iota of thought, though if true would wipe out the evolutionary explanation.
Leaving aside these problems, the explanation has to confront the fact that different societies have different rates of murder, and that a given society may have murder rates that vary significantly even within the timespan of a single human lifetime. How genetics or evolution accounts for that, who knows? Nevertheless, the answer lies in evolution.
These so-called explanations explain nothing. They are the modern scientisms' equivalent of "this is due to the Will of God". The Will of God obviously determines everything. The tornado came because of the Will of God, and I survived it because God willed it so. We learn of the Will of God in retrospect only, of course; and from prophetic guesses.
Likewise, all phenomena that arise in anything biology obviously arise from genetics and evolution; and so such similar pseudo-explanations spring like weeds.
I use scientism here to mean the habit of latching onto science as a religion or an ideology; and coming up with seemingly "scientific explanations" without asking whether these explanations actually explain anything, or whether the explanation can be tested in the scientific method.
The main long-term effect of such scientism, I fear, is to vitiate science itself. People are able to glibly write about "the end of science" because they see that such scientisms do "explain" everything. That these are ad hoc; just-so stories. There is an enormous amount of hard work remaining to be done to build and establish the causal chains that would constitute a true explanation.
We actually have to be quite careful. To quote Adolf Grünbaum (from a different context):
Quite generally, ever since Francis Bacon taught, it has been known that, at least in the case of causal hypothesis, the mere deducibility of some data from some such hypotheses (together with known initial conditions) does not suffice to qualify the hypotheses as explanatory, nor does it quality the data as supporting evidence for the hypotheses. To believe that it does is to indulge in dubious hypothetico-deductive pseudo-confirmation. What is being overlooked by such a belief is that, although the causal hypotheses (in conjunction with the known initial conditions) entail the particular data, the hypothesized causal factors are often actually causally irrelevant to the data which are to be explained. If the causal hypotheses are to be explanatory, they need to meet further well-known epistemic requirements, such as furnishing suitable 'controls' instantiating actual causal relevance.
