A hormone is something produced in the body that circulates in the bloodstream and then influences the activity of living cells that are far from where it was produced. Because hormones travel to their target tissue, they are sometimes referred to as signaling molecules. For example, estrogen is produced by the ovaries, but effects the functioning of cells in the heart, uterus, breast, liver, and brain. Any molecule produced in the body that travels to another tissue via the bloodstream for its effect is classified as a hormone.
Many hormones affect social behavior, often by directly influencing some aspect of brain function, although there are certainly other routes to influencing behavior. Hormones can only affect tissue that has receptors for them. If there is no receptor for a hormone in the brain, it cannot affect brain function. However, many hormones do have receptors in the brain. In social psychology, some of the most researched hormones include testosterone and estrogen (often called sex hormones), as well as vasopressin and oxytocin. Although it is often said that testosterone is the male hormone and estrogen a female hormone, is should be stated that all people have all of these hormones—it is just the amount that differs.
Hormonal links to human behavior are of interest to a variety of social psychologists but perhaps especially to those who are trying to understand topics like falling in love and sexual motivation, dominance hierarchies, and the reasons that differences exist in the behavior of men and women.
Testing for Hormone and Behavior Connections
Psychologists who are interested in understanding the role that hormones play in shaping human behavior rely on several types of research approaches. These would include animal research where hormone levels are experimentally altered, studies of humans with certain types of disorders that change the levels of hormones, direct measurement of hormone levels via immunoassay, and studies that take advantage of natural variations that occur in the levels of some hormones. With each approach, the psychologist is trying to see if changes in hormone levels relate to changes in behavior in a predictable way. For example, a social psychologist might be interested in the reasons that more females choose to major in psychology (study of human behavior), while more males major in engineering (study of mechanical objects). Although most psychologists would certainly agree that social attitudes play a major role in career choice, the potential role of biological differences could also be important. In fact, girls from a very young age appear to be more people oriented (playing with pretend people, drawing more people) and are shown to be more empathic and interested in feelings on a variety of indicators, while boys from a young age seem more drawn to nonliving mechanical objects and later show better spatial skills, such as the ability to visualize complex objects from a variety of angles. Because this sex difference is found all over the world, one might wonder if there is some biological basis for this difference. To test this, a psychologist might look at whether levels of hormones relate to differences in people orientation, empathy, or mental rotation skills.
First, one might measure the level of hormones in the bloodstream via immunoassay, or saliva samples could be used. If the psychologist thinks that testosterone might relate to performance on a test of spatial skills, it would be testosterone that would be measured. If persons with high testosterone levels have better spatial skills, the idea would be supported. It is also true that the levels of hormones vary in a predictable way across time; this knowledge can be used to test the effects of hormones without taking direct measures. In women, the levels of estrogen and progesterone change across a month due to the menstrual cycle. A psychologist might wonder if high estrogen levels actually worsen performance on spatial skills tasks. Thus, he or she might give a test of spatial skills at day 12 (when estrogen is high) and at day 1 (when estrogen is low). If the scores at day 12 are lower than would otherwise be expected, the idea would be supported. Testosterone, too, follows a predictable pattern of rises and ebbs, though not a monthly one. The average testosterone level is higher in the fall and lower in the spring, so a psychologist could measure a behavior at two times in the year is a similar fashion.
Animal models are often very useful, as many of the sex differences of interest to a social psychologist can be seen in other species as well. Although a person might suppose that the question of college major could never be investigated via animal models—after all, mice do not go to college—but male rats do show better spatial skills than females. There are tests of spatial skills for rodents that rely on maze-solving ability. If a psychologist wonders if prenatal levels of testosterone are affecting spatial skills, a developing mouse can be injected with extra testosterone if it is a female, or, if male, testosterone effects can be eliminated. If the females with extra testosterone grow up to be unusually good at solving mazes, especially if the males denied testosterone grow up to unusually poor maze solvers, the role of testosterone on maze solving would be supported. Of course, mice are not people, and ideally a psychologist would do an experiment with people, but the obvious problem is that parents are (of course) reluctant to allow the hormonal environments of their unborn children to be manipulated. However, some children are born with conditions that alter prenatal hormone environments. A condition called congenital adrenal hyperplasia (CAH) causes a lack of an enzyme needed to tell the adrenal glands to stop making the male hormones, so they are exposed to levels that are much too high during prenatal development. The problem can occur in either males or females. Upon birth, the problem is almost always diagnosed and the enzyme supplied via medicine, and the problem is no longer present. Girls with CAH are of great interest to a social psychologist interested in the role of prenatal hormonal environments on behavior. These girls self-identify as girls, and society sees them as girls (i.e., they are getting all the same social messages about what it is to be a girl as any other girl); the difference is in the prenatal hormonal environment. In the example about college majors, a psychologist might try and find out if girls with CAH have better spatial skills or were more likely to play with mechanical objects over dolls as children.
Generally, a psychologist would want to see several different types of research approaches coming together to support a role for a particular hormone on an aspect of human behavior (referred to as converging evidence) before concluding a behavior is influenced by hormone levels. In the previously mentioned examples, all of these types of research have been done, and all support the idea that hormones do have some influence on spatial skills. It should be noted that psychologists who conduct this type of research differentiate between organizational effects of hormones and circulating effects. Organizing effects refer to prenatal exposure and how this might alter the brain and behavior; circulating effects refer to current levels and how current amounts of hormones in the body might affect behavior. It is possible for a hormone to have one type of effect on a behavior but not the other, both effects, or neither.
What Is Known about Hormones and Behavior
Estrogen has myriad effects on the brain and body. Those relevant to social psychologists include pathology (depression, borderline personality disorder), verbal memory, motivation for sex, and emotional jealousy. The brain has estrogen receptors, and estrogen has the direct effect of raising the levels of the neurotransmitter serotonin. This is important because serotonin is important to understanding depression, and perhaps schizophrenia and borderline personality disorder as well. Estrogen supplementation has been shown to alter the symptom expression of these disorders, whose courses and prevalence rates are different for males and females. As for cognition, several types of research suggest that estrogen may increase performance on tasks that can be related to verbal skills or verbal memory and may decrease performance on certain tests of spatial skills.
Although it has been widely believed that testosterone promotes aggression, this is only partially true. The best research suggests that testosterone is more related to a desire for social dominance and power, rather than aggression per se (although desire for power may lead to aggression at times). Other research suggests that testosterone increases sex drive. As for cognition, several types of research support that testosterone has some effect on the expression of spatial skills, both organizational and circulating levels. Most research on circulating levels suggests that the low male range is optimal for enhancing spatial skills.
Oxytocin and Vasopressin
Oxytocin acts directly on both the nucleus accumbens and amygdala and increases after sex, promoting a feeling of bonding. Oxytocin has also been found to increase positive feelings about other people. Vasopressin levels and receptors within the brain for this hormone are higher in species in which males and females form monogamous relationships and who provide care for their young. Both of these hormones seem to promote affiliation needs in humans. These hormones increase when a person falls in love. Animal research suggests that these hormones are actually causing affiliative behavior and social bonding since experimentally altering these levels of these hormones leads to major changes in pair bonding and parenting behaviors. Many social psychologists think of these as being attachment hormones, and oxytocin is sometimes called the mothering hormone.
It is important to realize that hormone-behavior effects are not one-way. This means that hormone levels affect behavior, but behavior also affects hormone levels. The best example of this might be the relationship with testosterone and competitive behavior. Raising testosterone levels seems to make animals more competitive, and with enough of a boost, this translates into an increase in fighting behavior. But, it is also true that being in a competition has the effect of changing testosterone levels. It has been shown that even competition by proxy, such as watching your favorite sport team win or watching a movie character win an important battle, leading to an increase in power will cause a rise in circulating testosterone levels. Thus, when psychologists find that circulating levels of hormones are related to a behavior of interest, they consider that the direction of cause and effect may go both ways, and conclusions about whether the hormone is causing a difference in behavior are tentative without converging evidence in the form of experimental designs.
- Geary, D. C. (1998). Male, female. Washington, DC: American Psychological Association.