We explored the social behavior of field voles in their crowded Malthusian nesting environment. Remarkably, parents would sneak into neighboring nests and kill the youngsters there whenever they got the chance. This is in stark contrast to a similarly crowded human urban or suburban environment, where adults killing non-kin children in other households is extremely rare. Which of the following is the most accurate and complete description of the ultimatecausal origins of this profound human/vole distinction?

a.
Humans have the unique ethical psychology allowing them to suppress competitive infanticide, voles do not.

b.
Humans have the cognitive virtuosity allowing them to understand the destructive long-term consequences of competitive infanticide, voles do not.

c.
Humans have the unique capacity to cost-effectively use adult-on-adult coercion to suppress competitive infanticide, voles do not.

d.
Humans have the unique ethical psychology allowing them to understand that competitive infanticide is evil and should be avoided, voles do not.

This is the main reason why competitive infanticide is a common feature of voles, but is not a common feature of human communities. Human beings have a unique ability among animals, which is the ability to think ethically. This is why our actions and behaviours are usually influenced by whether or not we believe that we are acting in a way that is fair and benefits ourselves and others. Even if humans believed infanticide to be practical, it is unlikely that they would engage in it on a mass scale because of ethical concerns.