Often, it is the "survival of the fittest."

The number of human beings that would consciously take another human life in circumstances other than in a moment of mortal danger to themselves, in a kill or be killed situation, is surely tiny? I imagine that would be when evolutionary processes take over, with a heady burst of adrenaline boosting latent testosterone.

Persuading another human being to kill another human being is another matter entirely and can be explained by manipulation of innate biases and scion-cultural (implanted) belief systems. War is a good example of that. A country is made up of individuals and individuals are extremely nuanced creatures. Spreading the idea that a 'country' is somehow 'evil' allows otherwise good people to take the lives of individuals they might otherwise be best friends with on a 1:1 basis. Generally it's powerful individuals with a similar view on the world that send off individuals to fight and die on their behalf. I don't know the last time a leader went to war, leading 'his' men on a horse.

Hunter gather tribes are not as violent as we think and when they recently showed a tribe from the Brazilian rain forest a film of modern warfare they couldn't understand the logic of it. Taking a life, animal or human, has a deep spiritual resonance for them and one life equates to another. Human on human violence is more likely to happen in agricultural societies where there is plenty to go round, like in the West. And as it's frowned on to kill our neighbours we find someone far away to kill instead. As Friedrich Nietzsche said, “Under peaceful conditions a warlike man sets upon himself.”

Many people, most I hope, can't get their heads around killing because it seems and feels so alien to them. But if social violence comes as a result of biological and environmental processes we can understand, why are those at the top of the food chain, our leaders, not talking about it? That bothers me.
Comparing us to animals has a logic but we are also distinct from them because we have a spoken language and can justify with thought, 'intelligence' and by persuading others to do our bidding. And it starts in the classroom.
Robert Sapolsky, professor of neurology and neurological science, speaks of the confusion of violence, the multiple levels of causality, in a very interesting TED Talk, "The Biology of our Best and Worst Selves." He gives a few examples of how individual humans, and groups of humans, changed their behaviour and attitude to killing, as adults, hang been around killing, almost like a switch was pressed. Interesting stuff.
In my view, we are primarily social creatures and rose to dominance because the group recognised the need for utility of the individual in order for the group to thrive. We are unique as a species insofar as children as young as two years old share and demonstrate empathy and embracing our differences, utilising them, got us here. Perhaps technology and the manipulation of violent acts by those who control the media, to make us appear super violent to each other so we can be controlled, has moved the goalposts and is making us feel more vulnerable than we actually should be, or need to be.

Not everyone nowadays is able to kill another human being as if it is a casual and normal part of life. As an example, soldiers who suffers from P.T.S.D., I have friends who served in wartime and are having a hard time adjusting to the fact that they killed someone, even though they were trained to do so. I also know some police officers who shot someone and have a hard time and suffer from P.T.S.D. after that. We have evolve to the point that killing is not an easy thing to do. I know some people that cannot even bring themselves to kill an animal. I was in the military and I was a police officer and I am so glad that I never had to kill anyone. I came close to shooting someone and I am so glad that it did not happen.

As a formerly religious person myself, I had thoughts of killing people. It had to do with my mindset -- the victim mentality, particularly. I carried concealed weapons (yes, more than one), I had made up my mind to die for Christ, I felt like I had to be part of something. When I went to holster my gun one morning, I realized that I couldn't even point a gun at a person, let alone shoot them. I stood there, alone with my embarrassment. I think it's because I felt like I had to defend my beliefs/way of life.

About the correlation yes the show Lucifer is just entertainment but Lucifer is from the Bible the correlation I was making was between creationism and evolution just because we come from murderous stock does it mean that we can't overcome that as a matter of fact the rate of people killing each other over the last Thousand Years has changed dramatically that's what civilizations are about but to me it's obvious the reason why it's still exist at all is because of where we come from

I don't understand the correlation between the show "Lucifer" and evolution.

Force of habit, we started some time pre-Habilis and haven't worked it out yet.

every creature eats something that is or used to be alive. watch chimps and you see us in our basic form.

Don't ask me. Why do people hate other people because of the color of their skin?