Birth order

Birth order refers to the specific sequence in which children are born into a family.

This concept is a major topic in psychology. Many people believe that being the firstborn or the last-born changes a person's character. Scientists have spent many years testing these ideas to see if they are true. While some researchers find small links to certain traits, most modern studies show very little connection between birth order and personality.

One of the earliest theorists was Alfred Adler, an Austrian psychiatrist who lived from 1870 to 1937. He believed that birth order leaves a permanent mark on a person's "style of life." This term describes how a person habitually handles work, love, and friendship. Adler argued that firstborns experience being "dethroned" when a second child arrives. This loss of being the center of attention might change them. He also suggested middle children might feel overlooked, causing "middle child syndrome." Younger children or only children might be pampered, which could affect their later personalities.

Modern psychology often uses the "Big Five" to measure personality. These five traits are openness, conscientiousness, extraversion, agreeableness, and neuroticism. In 1996, Frank Sulloway published a book called "Born to Rebel." He argued that birth order strongly affects these Big Five traits. He claimed firstborns are more conscientious and socially dominant. He also suggested they are less agreeable and less open to new ideas. However, many other scientists disagree with Sulloway. Large studies have found almost zero effect of birth order on these personality traits.

Researching birth order is difficult because of "confounding variables." These are outside factors that might confuse the results. For example, family size is often related to birth order. Large families often have lower socioeconomic status, which means they have less money. A third-born child lives in a larger, poorer family than a firstborn. It is hard to tell if a trait comes from birth order or from family wealth. Because of these complications, many scientific reviews find only minimal effects. One study of 6,315 young men in Switzerland found no substantial effects at all.

Some scientists focus on intelligence rather than personality. A metanalysis by Polit and Falbo in 1988 found that firstborns and only children often score higher on verbal ability tests. Robert Zajonc proposed a "confluence" model to explain this. He suggested firstborns spend more time in intellectual adult environments. He also noted a "tutor effect," where older siblings teach younger ones. This might increase the intelligence of the older sibling. However, other data suggests these IQ differences might just be an artifact of family size and social status.

There is also a specific theory called the fraternal birth order effect. This theory looks at the sexual orientation of men. It suggests that the more older brothers a man has, the higher the probability he will be homosexual. Some studies suggest each older brother increases these odds by about 33 percent. Other large studies suggest a smaller increase of 15 percent. This effect does not seem to happen in women or with older sisters. It also appears to only affect right-handed males.

Scientists have several ideas about why this biological effect might occur. Edward M. Miller suggested it might be an evolved mechanism. This could reduce competition between brothers in a family. Another theory involves the mother's immune system. It is thought that as a mother has more sons, she develops immunity to certain male antigens. This immunity might affect the brain during development. Researchers are still studying whether these biological changes are truly linked to birth order or to other genetic factors.