The Grapevine

Birth Order May Predict Intelligence And Illness In First-Borns, But Vitality In Their Siblings

siblings
Being born first predicts a range of risks and advantages to children, which may stick with them for life. Javier Kohen, CC BY-SA 2.0

It isn’t often you hear themes of destiny in scientific literature, but birth order stands out like a sore thumb. While most research relies on people having agency in their actions, investigations into the effects of being born first, second, or someplace further down the ladder seem to say part of our future is already written.

These studies can’t predict everything — we do write our own tickets, after all, at least to a certain extent (philosophers are still out on that one) — but they do help shed light on the ways in which our environments groom us to lead one type of lifestyle over another. Scientists have found links between our personalities, our health, and our ability to sustain relationships — all determined by whether the universe decided to put your core self, your essence, inside the head of one child or another.

Health Differences

As temporary only children, first-borns are given a bevy of advantages. They receive all of their parents’ affection and earn all the spoils. But it comes with a price. A childhood of excess has been found to lead to several health complications later in life. First-borns are more prone to diabetes, metabolic disorders, and obesity, the last of which shouldn’t come as much of a surprise. Parents who want nothing but the best for their pride and joy tend to overfeed them.

Parents also tend to helicopter over their first-borns when it comes to their vaccines. A great deal of research suggests a link between first-borns and the development of allergies, asthma, and immune-related disorders. Anxiety plays a part. Statistically speaking, worried parents of an only child will typically rush to get every shot and injection pumped into their kid’s veins to prevent future illness more so than they end up doing for future children. As a result, vaccine-related emergency room visits tend to be much higher for first-borns than later siblings.

All this panic about doing parenting “right” has an upside. First-borns generally don’t engage in as much risky behavior compared to their younger siblings, especially their youngest. The baby of a given family is usually more likely to exhibit addictive tendencies, such as drinking and smoking, and engage in sexual behaviors earlier. In contrast to the strict parenting styles of the first-born, last-born children tend not to get as much attention, which, again, can either be helpful or harmful to their development.

A Note On Siblings

Before discussing the personality traits that differ between siblings, it’s important to keep in mind the many ways in which families operate. Health outcomes, too, come from a set of constraints. Lower-income families might not show the same preference of vaccinating their eldest child more than their youngest, simply because other things take priority, like food and paying the bills. In this sense, financial limitations skew the average data, which, it should be said, isn’t a small point.

A study from Ohio State University in 2006 found older children aren’t necessarily smarter than their younger siblings, as other research has suggested; rather, the majority of that research looked at large and small families, instead of siblings within the same family. When the OSU team controlled for family size, they determined intelligence levels correlated to how old mothers were when they had their first child. “In reality, if you look at these larger families, the fourth-born child is just as intelligent as the first-born,” said lead author Aaron Wichman at the time. “But they all don't do as well as children from a smaller family.”

Another factor psychologists have come to observe is a phenomenon called the “Sibling Niche Theory.” In every family, the theory states, children look for their respective roles. Older children typically fall into a leadership role, middle children find a mediating role, and younger children settle into an introspective — and sometimes rebellious — role. At the same time, they compete for limited resources.

“They’ve got to differentiate themselves in some way to get the attention that they need,” said Dr. Corinna Jenkins-Tucker, professor of family relations at the University of New Hampshire. Sometimes those roles are fads kids grow out of, but other times they stick around for life.

Personality Differences

Each family operates with different constraints, but psychologists have found several sweeping differences between kids born first and those thereafter. The eldest kids, for instance, are more likely to succeed in school because they learn a firmer sense of grit and determination from parents who play tough. Part of that upbringing nudges them toward the role of a leader. First-borns may face more freedom when it comes to their diets, but less so when their grades are on the line.

Kids born later in the food chain, with older siblings having already gobbled up other niches, turn to whichever spots they can get their hands on. “The baby of the family can be a little more irresponsible,” Jenkins-Tucker said. “Sometimes it’s conscious, sometimes it’s not.” A girl might see her older sister as the jock of the family, so she turns to science. Or it may simply be that soccer strikes her, at some deeper level, as “her sister’s thing,” so she finds her uniqueness elsewhere.

Where first-borns are the dominant forces in the house, occupying a role somewhere between parent and peer to their other siblings, and the baby of the family is avoiding an existential crisis, the middle child also merits attention. Almost in sync with their place in the family tree, middle children tend to be more even-keeled than their siblings at either pole. They mediate, Jenkins-Tucker says. Some research also finds them to be more faithful in relationships, prompting some relationship experts to suggest marrying a middle child a way to avoid divorce.

Not Written In Stone

Where you’re born relative to your siblings can’t predict everything about you. Bill Gates, the wealthiest person alive, is the baby of his family. If we look to his fortune and philanthropy as markers of success, he certainly breaks the mold. Kurt Cobain, meanwhile, was the oldest of his siblings and struggled with devastating heroin addiction in the years leading up to his suicide.

Birth order can’t do it all. Instead, science is finding the complex relationship between nature and nurture demands we consider both sides simultaneously, not just one or the other. Our upbringing may affect our trajectory, but once we leave the nest, it’s up to us to decide whether we stay on course.

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