The human body evolved over eons, slowly calibrating to the African savanna on which 98 percent of humankind lived and died. So, too, did the human brain. Evolutionary psychology is the study of the ways in which the mind was shaped by pressures to survive and reproduce. Findings in this field often shed light on "ultimate" as opposed to "proximal" causes of behavior. Romantic jealousy and mate guarding are proximally intended to keep one's relationship intact. Ultimately, though, the behavior can be explained by the fact that for most of human history, losing a romantic partner jeopardized one's ability to reproduce and raise children.
Natural selection has a lot to do with human behavior. In fact, our behavior is naturally selected just as our physical traits are naturally selected. We are much taller and live longer than our ancestors. Through centuries of generations, evolution has helped us pass along adaptive behaviors that promote our reproduction.
Evolutionary biologist Robert Trivers proposed a number of theories on evolutionary psychology, including why we engage in reciprocal altruism, the nature of sex differences, and parent-offspring investment. Altruism among strangers, for example, can naturally develop because people cooperate with the expectation of receiving similar treatment from others.
Our hunter-gatherer ancestors passed down behavioral traits that are, for the most part, advantageous to us. For example, we are mindful of danger in dark alleyways. This caution is innate and within our behavioral make-up. And our predetermined response to gravitate to that 800-calorie Cinnabon can wreak havoc, but our ancestors made us do it.
Juggling our ancestral tendencies with the demands of modern-day living can be a struggle. This phenomenon is known as evolutionary mismatch—when we find ourselves in an environment inconsistent with our ancestral conditioning.
A good example of such mismatch is the contemporary diet: Ten thousand years ago, people battled starvation. They had to pile on the necessary calories just to survive certain lean times; high-fat meats and high-sugar foods were a luxury. Today, however, fatty foods and processed sugars are readily available at low cost.
Many of the behaviors people exhibit have been tools for self-preservation: Homo sapiens jealously guard their romantic partners because competition for mates has always been harsh. Everyone cherishes their closest kin because it's in one's best interest to preserve one's genes. Humans also crave social interaction to encourage cooperation, further increasing the chances for survival. Many of these behaviors are innate: How people react and interact with one another is spelled out in DNA.
Fight or flight refers to the human body’s built-in response to a perceived threat: It prepares the body to either face danger or quickly run from it. During flight or flight, the brain releases stress hormones, pushing the body into high alert. The heart rate rises, muscles tense, and thoughts race. While the modern-day human does not face the same threats as our ancestors did, the fight-or-flight response system remains intact.
Any fearful situation can trigger it, whether it is physical danger or a stressful event, like running late for a meeting. In people with anxiety, the fight-or-flight response is more readily triggered, the brain sees certain situations as threatening, even when there's no actual present danger. In fact, there is a tendency for this response to move into overdrive in anxious individuals.
Kin selection is the theory that our calculations about genetic relatedness to others (conscious or unconscious) are powerful drivers of behavior. Most people favor, and will make sacrifices for, immediate kin as opposed to distant relatives, and blood relatives over strangers. This ensures the survival of genes through the survival of the people who are closely related to us.
In evolutionary parlance, reproductive success is called reproductive fitness, a measure of how well an organism or a person is adapted to their environment. Men committing foolish or heroic acts that increase status or attractiveness are acting in ways that increase the odds of reproduction, and attempting to maximize reproductive fitness. Reproductive fitness also measures how well an organism is adapted to its environment.
The differences in parental investment—the energy and resources invested in an offspring—lead the sex that invests more (females, in most species) to focus on mate quality and the sex that invests less (males) to seek quantity. In humans, we expect choosiness in females and aggression between males as they vie for females.
Our emotional complexity differentiates us from other members of the animal kingdom. Evolutionary psychology seeks to explain how our emotions and other aspects of being human served as advantages to our ancestors. Like other social primates, we experience emotions beyond primal fear and anger.
People reject evolutionary psychology for ideological reasons. With sexual behavior, for example, there is the notion that the field justifies people’s behaviors and actions. Our present-day traits and characteristics had survival value for our ancestors, and these traits survived because the genes they are linked to were selected and now remain part of our genetic makeup. Shouting evolution made me do it seems so convenient.
This refers to common but faulty logic wherein people assume that because something is "natural" it is therefore "good" or just. Violence and aggression are found in all human societies, but that does not make this acceptable behavior. No endorsement is implied in a discovery of what is natural. The general public commits the naturalistic fallacy in thinking that evolutionary psychologists endorse certain findings (such as violence or rape), when in fact evolutionary psychologists are simply outlining reasons that these behaviors may occur.
The moralistic fallacy is the false belief that the world operates as we wish it would, that what ought to be is in fact the truth, or that because we wish something were not true, it cannot be true. People sometimes reject evolutionary theorists' findings about human nature because they do not want to believe that said findings are true.
Both sides of the political aisle accuse evolutionary psychology of numerous ills. Among many arguments, for example, conservatives on the right fear that this field of study absolves people of responsibility, while liberals on the left fear that accepting inherited differences hinders the goal of social equality.
Feminists are not keen on the idea that women are inherently different from men. Such differences, they think, would force women back in time, losing ground in equal opportunity and equal pay, for example. They also feel that people can use evolutionary psychology to explain away misogyny, poverty, sexual misbehavior, among many areas.
More and more studies show that homosexuality is genetic. However, being gay doesn’t fit so neatly into the theory of natural selection. Why would nature select for homosexuality if reproductive success is a moot point? But there are valid reasons according to evolutionary biologists. For example, gay aunts and uncles can invest more time and resources in rearing the offspring of close relatives with whom they share part of their genetic makeup. Maybe homosexuality emerged because it benefits entire groups.