Evolutionary Psychology
Since Steven Pinker showed that humans have an instinct for language, the question that confronted him was how that instinct was acquired. He found the answer in the field of evolutionary psychology. If a particular behavior is common among humans, that behavior probably contributed to the ability of their human ancestors to survive and pass along their genes. This is the psychological equivalent of evolutionary biology, which answers that if a particular physical characteristic is common among the individuals of a species, that physical characteristic probably contributed to the ability of their predecessors to survive and pass along their genes. Note that Steven has publicly tangled with Stephen Jay Gould over the scientific legitimacy of evolutionary psychology, and has been forced to respond to people's objections against a biological view of human nature, but says that there's no inherent contradiction between evolutionary psychology and the concepts of free will and moral behavior.
These are some key concepts in evolutionary psychology. The origin of species and functional design of living creatures in the natural world are due to natural selection. Natural selection is defined as the differential survival and reproduction of individuals in a population based on their inheritable traits. Psychological traits are as valid as any other traits on which natural selection can act. Psychological traits have a genetic basis in the brain, and therefore can be inherited. Currently represented psychological traits in human beings represent successful adaptions to various previous environments.
Religious Beliefs
In the book Whence Religious Belief, Steven speculates on how religion fits into a mind that should reject that which can't be proven. "In culture after culture, people believe that the soul lives on after death, that rituals can change the physical world and divine the truth, and that illness and misfortune are caused and alleviated by spirits, ghosts, saints, fairies, angels, demons, cherubim, djinns, devils, and gods. According to polls, more than a quarter of today's Americans believe in witches, almost half believe in ghosts, half believe in the devil, half believe that the book of Genesis is literally true, 69 percent believe in angels, 87 percent believe that Jesus was raised from the dead, and more than 90 percent believe in a god or universal spirit."
"The common thread of religious practice in all cultures: religion is a technique for success. Ambrose Bierce defined 'to pray' as to ask that the laws of the universe be annulled on behalf of a single petitioner confessely unworthy. People everywhere beseech gods and spirits for recovery from illness, for success in love or on the battlefield, and for good weather. Religion is a desparate measure that people resort to when the stakes are high and they have exhausted the usual techniques for the causation of success - medicines, strategies, courthsip, and, in the case of weather, nothing."
"What kind of mind would do something as useless as inventing ghosts and bribing them for good weather? How does that fit into the idea that reasoning comes from a system of modules designed to figure out the work works? The anthropologists Pascal Boyer and Dan Sperber have shown that it fits rather well. ... Peoples know there is a humdrum world of people and objects driven by the usual laws, and find the ghosts and spirits of their belief system to be terrifying and fascinating precisely because they violate their own ordinary intuitions about the world. ... Beliefs about a world of spirits do not come from nowhere. They are hypotheses intended to explain certain data that stymie our everyday theories."