Why haven’t murderers reached 100% penetrance of the human population?
Do you think there is a “murder” gene? Or genes that make people prone to violence?
As far as being prone to violence I would say there is no human population that hasn’t demonstrated this tendency.
Some have, historically, been better at it than others; but the tendency to violence, and organized violence - is a human universal.
Do you think people who kill people against the laws and customs of their people tended to have higher or lower reproductive success? Usually the penalty for such is death, exile, or imprisonment - all three which tend to curtail reproductive activity.
Science is now showing people who have murdered people or have very violent outburst tend to not have a certain part of the brain working that produces a chemicals inhibiting such violence as normal people have.
Not letting these people off the hook..they should be in jail but one day medical science will be able to diagnose, then cure through an operation or drugs this inactive chemical condition before they do kill somebody.