The Birth Order Effect

How Birth Order Influences our Personality and Health


There have been many experiments to determine whether the birth order of siblings truly influences each child's personality. Although there is no incontrovertible proof, scientists have discovered many strong trends. Frank J. Sulloway, a leader in birth order research, compares differing sibling skill sets to Darwin's theory of evolution; he suggests that siblings will choose different hobbies and interests in order to avoid competition and comparison. Being the eldest has benefits, in this case, because the firstborn is able to select a "niche" first. However, what attributes can generally be associated with each sibling? Combining the results of several studies, I have examined traits and trends to produce this analysis of common characteristics of siblings.


Sharpest Crayon in the Box?

Numerous studies have been conducted to determine if a firstborn child is more intelligent than his or her younger siblings. Zajonc's confluence theory suggests that a household's intellectual environment is higher for the first child, as the eldest child is more exposed to the adult world than his or her younger siblings. However, sibship density often throws a wrench into this equation; many years between siblings manifest a higher intellectual environment than few years. Additionally, Joseph Price discovered that in families of two, the eldest child spends approximately half an hour more quality time with parents per day than the younger, significantly improving the child's intellect. The firstborn has the opportunity to be the only child in the house, a privilege younger siblings do not experience, and this often seems to result in a higher intelligence level. Firstborns tend to be assertive, confident, dominant, and often perfectionists but also fearful and defensive about making mistakes.

Diseases: Diabetes, Heart Disease

Being the firstborn certainly has its benefits. However, studies have shown that high parental demands and expectations for their oldest child, as well as the pressures the perfectionist firstborn often puts on him- or herself, often causes depression. Additionally, studies from New Zealand and the University of Auckland are showing that firstborns have a higher likelihood of having cardiovascular disease or diabetes. The bodies of firstborns resist insulin more than the bodies of their younger siblings—up to 21% more! Firstborn children also have much higher blood pressure than their younger siblings. Scientists speculate the uterus of the mother might adapt after the first pregnancy in order to give nutrients more easily to the placenta, thus putting later children at a lower rate for the aforementioned diseases.

FUN FACT: Every man who played James Bond was a firstborn.


Squashed in the Middle

Although many middle children feel neglected and complain about their position sandwiched between the successful older child and spoiled younger sibling, studies are showing that being a middle has its perks. Eight of every ten middle children remain faithful to romantic partners, which is much higher than the percentage for firstborns (65%) or lastborns (53%). Middle children are often more empathetic, articulate, and understanding than siblings, and they display better negotiating skills than their sisters and brothers. Although middle children have a much higher likelihood of moving far away from their parents, ninety-nine percent of middle children desire their own sons and daughters. Fifty-two percent of presidents were middle children.

"We refer to middle children sometimes as justice-seekers," shares Dr. Catherine Salmon, the author of The Secret Power of Middle Children. "One of the things they often experience in the family is sort of being the underdog . . . and they tend to sympathize with the person who is not the focus of all of the attention."

Disease: CFS, Depression

New studies are hinting that middle children have a higher chance of ending up with chronic fatigue syndrome (CFS) and depression. Scientists are tying these trends to feelings of neglect and abandonment during childhood. On the plus side, middle children seem to have a five percent lower chance of gum disease.

Catherine Salmon, Ph.D

Faculty Experts: Catherine Salmon-The psychology of middle children and birth order
NPR Interview

An NPR interview was conducted with Dr. Catherine Salmon and Katrin Schumann, the authors of "The Secret Power of Middle Children." The interview goes slightly more in depth than the video. It is interesting but not essential to the project.


Baby of the Family

The youngest children are often the most independent and even spoiled of the family because parents are quite indulgent with the littlest son or daughter. Unlike the first child, whom the parents were constantly hovering over, the youngest children has much more freedom and is frequently more creative. Youngest children often feel the need to bring attention to themselves because they may feel outshone by older, more successful siblings. Therefore, they develop a keen sense of humor and charm. Many successful entertainers were youngest children, including Stephan Colbert, Eddie Murphy, and Billy Crystal.

Disease: Addictions

Parents' leniency may have a negative effect on their youngest children. According to Dr. Oz, the youngest children are "thrill/pleasure seekers" and have a higher chance of ending up with "addictive behavior, which can range from compulsive eating and drinking to sex." In a study done in a Kenyan drug rehabilitation center, it was discovered that 33.3% of the patients at the center were youngest children, the highest amount. First and middle children each made up 28.6% of the patients, and only children only made up 7.6%.


Focus of Attention

The rumors about "Only Child Syndrome"—that only children are spoiled, snobbish, and incapable of dealing with others—have not been proved by science and are often untrue. In fact, only children are often the sole focus of their parents' attention, a luxury children with siblings do not experience. They are highly exposed to the adult world, and therefore only children often become confident leaders with characteristics much like those of the firstborn: responsible, creative, high-achieving, and often a perfectionist. High intelligence levels may be caused by the extra time and attention parents are able to lavish on only children. However, an only child may struggle to relate to children his or her own age because he or she has no other children in the household. Dr. Ben Dattner, PhD, says that only children are "more inclined to do work themselves rather than to delegate."

Disease: Obesity

Unfortunately, studies in Copenhagen only children are more likely to develop weight problems. The study reveals, "Only children had significantly higher odds of obesity both in childhood and in young adulthood compared with children with siblings."
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FUN FACT: In a 2010 government census, 19% of households had only one child.