The Sociobiology of Humans
Evolutionary psychology is a fairly new discipline that focuses on the study of the evolutionary basis of social behavior in humans. DarwinOpens in new window, who introduced the theory of evolution in On the Origin of Species by Means of Natural SelectionOpens in new window (1859), focused largely on physical traits.
Evolutionary psychologists argue that social traits (behavior, thoughts, and emotions) have also evolved by way of natural selection.
General principles of the theory of evolution are as follows:
- Organisms vary in their characteristics.
- Organisms are engaged in a struggle for survival. Some organisms will survive and others will not survive.
- Some characteristics will lead to greater survivability and greater reproductive success.
- One’s descendants are also likely to have those characteristics that led to greater survivability and reproductive success. Therefore these successful characteristics themselves survive.
In his classic text, Darwin explained how a physical trait such as the bone weight of a bird or the camouflage coat pattern of a wild cat could lead to greater survivability of that individual and of its species.
Evolutionary psychologists argue that psychological/social traits may also lead or may have led to greater survivability for humans. For example, an evolutionary psychologist may argue that the tendency for a mother to love and be attached to her offspring creates a survival advantage for our species. The fact that this characteristic tends to be a part of our nature is precisely because it is advantageous; those women who loved their children took care of their children. This trait, loving children, was passed genetically to their own children and thus is a common trait in our gene pool.
To explain the existence of a characteristic in our gene pool, evolutionary psychologists appeal to the hunter-gatherer era of humans because this type of cultureOpens in new window existed for much of our evolutionary history, possibly for as long as two million years.
Evolutionary psychologists have discussed traits that are clearly advantageous, such as loving one’s offspring, but they have also discussed abnormal characteristics and explained how they may have evolved.
For instance, paranoia may have evolved and thus remains in our gene pool because it would have been advantageous to be vigilant (what would now be considered hypervigilant) during the hunter-gatherer period, when humans faced very real physical threats from predators on a regular basis.
As another example, clinical depressionOpens in new window, a syndrome involving many traits including sad mood, negative thinking, and low activity levels, may have evolved as a way for humans to conserve energy; the depressed person tends to remain at home, expending very little energy.
An application of evolutionary psychology that is controversial is the explanation of sex differences in mating behavior. Some evolutionary psychologists, including Buss (1994), have argued that women and men have developed very different mating strategies and mate preferences because doing so has led to greater reproduction of the species.
Buss presents data that suggest that across cultures, men tend to prefer polygamy, whereas women prefer monogamy. The evolutionary explanation is based on the number of sex cells that women and men possess. Men produce millions of sperm per day. It is evolutionarily advantageous for the man to use as many of these sex cells as possible. If he impregnates a female, she is out of commission for nine months, and thus it is to his advantage to impregnate a different woman.
Put bluntly, he would desire to impregnate as many women as possible. (This reproductive desire is not necessarily conscious, but those men who prefer polygamy would have produced more offspring, and thus this preference is common in men.)
By contrast, women have only a few hundred sex cells (eggs) in a lifetime. A woman’s eggs, being few in number, are precious to her. Also, once she is impregnated, she is nearly always unable to become pregnant again for nine months. If she is to be a reproductive success, she will take care of this fetus.
It is to her advantage to attract a man who will stay with her during the pregnancy and for a period of time after the baby is born, and possibly for the entire time that she takes care of the child. Therefore woman will tend to prefer monogamy.
Another argument made by Buss and others is that women and men evolved to prefer different qualities in mates. A man prefers youth and beauty because these are signals that a woman is capable of childbearing (younger women are obviously more fertile, and beauty is described as a sign of physical health and therefore fertility).
By contrast, a woman prefers a man with resources so that he can help to take care of her and the child or children. In modern times, the best resource is money. Additionally, older age tends to be associated with more resources, and thus women are attracted to older men.
Evolutionary psychology is a hot topic today. It is both popular and controversial. Excellent introductions to the topic include Gaulin and McBurney (2001), who discuss the main concepts of evolutionary psychology, and Buss (1999), hwo covers research studies on evolutionary psychology.