There are many misconceptions about human nature, from the tabula rasa theory of mind to the religious or ethical pronouncements about fundamental evil or fundamental good. Evolutionary theory, along with the philosophy of naturalism on which it is based, provides many key insights into the realities of human nature.
One rather unfortunate mistake - or rather, oversimplification - made by many social scientists and anthropologists in the past is the assumption of tabula rasa. Under this assumption, the human mind is literally a "blank slate" that is infinitely malleable by any imaginable cultural force. In this view, it is equally likely for a human to like steak or insects, to call a color red or purple, to favor monogamy or polygamy, to see the natural world as an objective reality to be investigated or an inconsistent source of evil powers. To the adherents of this viewpoint, all variation in human perspectives is caused by cultural factors; the human mind alone has no particular identity and no innate predispositions.
Following logically from this view came the extreme form of cultural relativism. The idea that only cultural factors varied combined with the politically correct view that all cultures are equally valuable to create cultural relativism, which argues that all cultures are equally correct. Cultural relativists argued that there was no objective reality outside of one's cultural context, and truth was truth only as determined by the group or culture.
There have been numerous experiments showing that cultural relativism is simply false. As mentioned in Language and Culture, the view that different cultures refer to the color spectrum in very different, arbitrary ways has been destroyed, replaced by the knowledge that color names correspond very well to the physiology of the human visual system. And it is simply illogical to claim that a tribal notion of stars being dropped pottery shards is equivalent to modern astronomy. And, as we shall see, the tabula rasa theory of mind is equally false.
Human nature was shaped through the forces of natural selection, like all functional features found in organisms. The reason that human nature is the way it is, is because it was adaptive to be that way in the past. Human nature, like all functional attributes of organisms, was determined by differential reproduction of varying entities in the ancestral environment. Certain behaviors, responses, or emotions were adaptive in particular situations in our ancestors' hunter-gatherer environment. Those that possessed these behaviors, responses, and emotions were more likely to reproduce than those who did not possess them; therefore the genetic predisposition toward those things was also passed down to the next generation. In time, the genes for those behaviors had become quite prevalent in the population, driving different alleles nearly to extinction. Of course, different genetic combinations of these adaptations could arise, but these too would be subject to the forces of natural selection. In this way, the seemingly automatic responses to many ordinary stimuli that we call "human nature" were hard-wired into our brains by natural selection at work. Humans have a battery of instinctual behaviors and automatic reactions to certain stimuli. For example, humans naturally jerk away from a hot object, shiver to keep warm, cringe or duck when an object comes close to the head, put our arms out when we fall, etc. Of course, these behaviors are shared with many other animals, in some cases all mammals and probably some others as well. So, while these reactions may have formed the basis for later evolution, they cannot be said to really form a part of what we call "human nature". That distinction is reserved for behaviors that are (or at least seem) uniquely human. It is common, especially in some religions, to declare that some things are intrinsically good or evil. While this may superficially seem to make sense - donations to charity are intrinsically good, H-bombs are intrinsically evil - this view overlooks the simple fact that objects cannot have moral value without humans to do the evaluating. Separated from human evaluations (and actions), these things are no more good or evil than a rock, a tree, or any other ordinary object.
It is also common to argue that human nature itself is intrinsically good or intrinsically evil. In the first place, this clashes with the free will that many philosophers place at the center of their theories of humanity. Second, this may represent (or seem to represent) observations about individual humans but does not generalize well to humanity as a whole. Third, the concepts of "good" and "evil" do not have real meaning outside of human evaluations, and hence human nature itself cannot be either. Finally, fundamental human nature is more properly seen as an adaptation to the situations encountered by our ancestors as they evolved, not as something with intrinsic moral properties.
Humans have a battery of instinctual behaviors and automatic reactions to certain stimuli. For example, humans naturally jerk away from a hot object, shiver to keep warm, cringe or duck when an object comes close to the head, put our arms out when we fall, etc. Of course, these behaviors are shared with many other animals, in some cases all mammals and probably some others as well. So, while these reactions may have formed the basis for later evolution, they cannot be said to really form a part of what we call "human nature". That distinction is reserved for behaviors that are (or at least seem) uniquely human. Despite assertions to the contrary, possessiveness in one form or another is a ubiquitous element of human existence. It almost certainly evolved from the territoriality of many monkeys, who protect their hunting grounds, and many times their mates, from potential rivals. Humans too have this possessive instinct; males and females alike resent being cheated on (though this arises for other genetic reasons as well), and no one likes to have his possessions stolen by a rival or a thief. Indeed, human possessiveness may have been one of the driving forces behind the evolution of the justice and fair play memes. It is worth noting that even communal tribes use the notion of possession, albeit differently than Westerners do. Tribes band together because individuals cannot survive alone in such an environment, but groups of individuals working together form a viable unit. As a result, possession takes place at the group, not the individual, level - tribes tend to be highly territorial, and many consider an intrusion onto their territory sufficient provocation for war.
The very human emotion of jealousy acts as an adjunct to possessiveness. Jealousy permits a person to desire to keep his own possessions while simultaneously coveting another's. Jealousy arises when a man sees another man with a more beautiful woman, a better-constructed home, or more and healthier children than his own. The jealous man would indeed be offended if someone tried to steal his wife, house, or children; yet he also sometimes attempts to steal another man's. This strategy can make good genetic and memetic sense, creating a desire to have items that will maximize one's genetic or memetic reproductive fitness.
Sexual behavior, a fundamental element of human nature, is also deconstructible through evolutionary analysis. Sociobiologists have found that men and women commonly make basic choices about mates due to genetic predispositions selected to maximize probable genetic reproductive fitness. Males have a tendency to look for young women with all these external signs of health and fertility - clear skin, fair hair, symmetrical facial features, and wide hips are all major factors. Biologically, males invest less in parental care of offspring, and therefore their best bet genetically is to impregnate as many females as possible.
Females, on the other hand, invest more care in the offspring biologically and, as a result, culturally. Also, a female cannot maximize her genetic fitness through many matings because of the biological reality that male initial investment is much less. As a result, females tend to seek older men with good social and financial status who seems as if he will give good parental care to the offspring she bears for him.
Love and empathy are commonly held to be the better side of our human nature, but they too are simply adaptations to the environment faced by our ancestors. Love as an emotion initially served two very simple functions (or perhaps one of the two, which then expanded its functionality): to enforce kin selection and to alert the presence of a suitable mate. Love would have been a quick, efficient "macro"; an emotion that was equivalent to the object of this emotion is genetically related and deserves help. This is a phenomenon called kin selection, discussed in Other Types of Selection - Section 2. Genes that favor love (and consequently, assistance) toward those who might share the gene tend to become more favored in the population, and thus the genes for love spread through the population.
Love also serves as an alert of a suitable mate. The feeling of love is a response to the presence of an attractive mate fitting the individual's expectations (at least roughly). This is the biological basis for the feeling of "love at first sight" - the object of the emotion is seen (instinctually) as a potential mate. The emotion continues even while a man and woman are a pair, and ceases when (instinctually) the mate no longer appears to be desirable. Those that feel strong emotions of love will probably attract better mates, and discriminate among mates more successfully, thus giving the genes for love an additional adaptive function.
Empathy serves a similar function, but its replicator is the meme. When a person empathizes with another, he generally seeks to relieve the other person's suffering or assist the person in one way or another. Empathy is probably most commonly felt by a meme adherent toward those that bear "markers" identifying them as adherents of the same meme. Actions taken to relieve the person's suffering would most likely rescue a copy of the meme in question, giving it additional chances to replicate.
Empathy can also be a meme-spreading, not just a meme-preserving, device. Those who are empathetic and take action to relieve others' suffering may become better-liked and respected, causing others to be more likely to adopt the empathizer's other memes. Also, those who are helped by the empathetic action may feel obligated to the empathizer, and take on his memes to reduce the obligation or to appear grateful.(source:http://library.thinkquest.org)