Evolutionary Biology is the study of how an animals or plants physical features came to be through the process of evolution. There are millions of fascinating things to look at in this realm. For example, Panda bears have five fingers and an extra thumb! But it's not exactly a thumb, it's a non-articulated spur on the wrist bone that elongated over time. It serves to help the Panda strip leaves from bamboo stalks. But why is it non-articulated, doesn't evolution allow a bear to grow an extra thumb? The reason seems pretty obvious from an evolutionary standpoint. All mammals evolved from a common ancestor which was a fish, probably related to the coelacanth. This creature crawled out of the water about 400 million years ago and eventually spawned (no pun intended) the amphibians, reptiles, birds and mammals. That ancestor had five bones in it's front and rear fins. This "design" has remained pretty much constant for the last 400 million years with no new appendages being added to the basic design no matter what the need. Some mammals such as horses, goats, pigs, sheep, dolphins and whales have lost toes or limbs through evolution, but no creatures I know have added limbs, fingers or toes. For example, birds sure could use a pair of arms with hands attached, but it's not in the original design, and while mutations do happen, they have to overcome a 400 million year heritage to propagate throughout the species. So the Panda doesn't actually get a 6th finger, it gets a bone spur which may become a new articulated finger, but it's not likely. Edward O. Wilson coined the term for this effect "phylogenetic inertia".
Evolutionary Psychology is the study of an animals behavior and how that behavior came about as a solution to living in its environment. Behavior is inherited through genes, not through teaching, although some teaching is needed for higher animals, mostly to prevent infant mortality due to making a bad move right out of the nest. Even creatures that are taught can still become fully developed adults without training which suggests that behavior is hardwired. Most often we call this instinct and even more often we leave ourselves out of this realm. Most people despise the notion that humans might be hardwired to do anything, that we have "free will", that all behavior is environmental (learned) rather than inherited (innate). The objection these people have is that if behavior is innate, if bad behavior cannot be "trained out" of the miscreant, then there is no hope for the "lesser races" of man. But it appears that this is just a false hope, that is constantly proved wrong, at least for those who read the daily newspaper in a diverse culture such as ours. Any time someone "flies into a rage" and commits some barbarous act, such as the Middle Eastern TV station owner who sawed his wife's head off, what you are seeing is innate behavior, behavior that is hard coded into the person. This guy was described as super nice, and he wanted to show how nice Arabs are by building "Bridges" (the name of his TV station) between American whites and Arabs. This face of his personality is the face he learned was approprate for being around Westerners. However, his act of rage while beheading his wife for filing for divorce shows the real person that evolution created, and that is what cannot be allowed to live in the house next door to civilized pople. Even when brought up in a civilized country, like, say, Britain, Middle Easterners constantly return to their roots and commit honor killings, murdering their own daughters, as well as committing terrorist attacks (the London attacks were carried out by 2nd and 3rd generation Arabic Britons), acts of intimidation, threats of violence, etc. People who are descended from British stock like white Americans are horrified at the idea of killing a beloved daughter. As a father of two daughters I am appalled that anyone could do that, even when they go against your wishes (and mine pushed that envelope), you can't just murder them! And yet these men revert to the their built-in behavior despite being born, raised and educated in a very civilized society. No amount of training can delete this behavior, because it's built into the brain through genes. The reason why these behaviors exist is that they are inherent, based on a breed of people (a race, or partially inbred group) that evolved in a society that treats women like beasts to be inseminated at will, and where like a breeder, a father chooses his daughter's mate. From an evolutionary standpoint, allowing the father to choose his daughter's husband is a good thing, it prevents the daughter from choosing a lower class husband, someone that could "pollute" the family's gene pool. But the Western world developed a different method, using class to establish a finite group of acceptable suitors. With this system, fathers could let their guard down some and allow their daughters some leeway in choosing a husband. It worked too, Western women have more freedom than any other society, made possible not through years of protests, but by hundreds if not thousands of years of evolution shaping the behaviors of both fathers and daughters. People who had the instinctive notions that conformed with Western societies norms had more children than those who didn't conform. Of course this requires people who do not conform to be removed from the gene pool, which happens by way of imprisonment or execution which European countries used to great effect. The result is that white people most often behave in a civilized manner, not because of their white skin, but because of centuries of "pruning" of non-conformists. Now, throw diversity in the mix, add in a bunch of people who have gone through a different pruning process where the cultural norms were different and thus, different behaviors became built-in, innate, automatic and you get a society where each person thinks the other is a barbarian. Hardly a recipe for harmony. Why are the prisons overflowing with blacks and hispanics? Because their notions of right and wrong are different from those of the white people who wrote the laws. If you just let the blacks and hispanics write the laws then the prisons would have virtually no one in them, because blacks and hispanics have not evolved under similar civilizing conditions. Now, give it a few hundred years (and stop the "conjugal visits") and blacks and hispanics will behave more like whites. Not due to training, but due to pruning. Of course you had better hope that the effect of phylogenetic inertia hasn't taken blacks and/or hispanics too far over the edge so that like the Panda and his five fingers, there are no remaining "civil" genes left in their genome. Think about what might happen to a good and decent person who might have arisen in Africa through a mutation for say, kindness. Might they have been killed just as most whites have been killed or driven out of Haiti, Zimbabwe, Kenya, and South Africa? The study of these behaviors and how they evolved and why they remain is really quite fascinating.