Morality is based on a humans brain chemistry with decisions in their everyday living environment. If one is brought up where killing others is an everyday norm, they will have no difficulties in deciding whether or not to kill another person, as their brain does not register this as something that is "wrong", so to speak. Morality is based off ones upbringing in circumstantial environments based on that environments social culture. When we register something as being "wrong", our brains light up with activity, adrenaline is released, our senses are heightened, and we go back to the primal instinct of "fight or flight", even if the fight is not physical and only verbal in context. Depending on said situation, morality is only determined by what our brains have been trained to perceive as "proper morals", and nothing more or less than such. It's not based on religion, nor is it evolution. According to biochemistry, it's based on what we are taught in comparison to the brains ability to decipher such instances as being "right" or "wrong" in said social culture.