Does Birth Order Affect Personality?

The only child has trouble sharing, the oldest is bossy, the baby always gets what they want, and the middle child is—well, stuck in the middle. Are these stereotypes, or is there truth to birth order differences? 

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Birth order only explains a small part of who we are, but personality variations definitely exist between siblings, says Frank Sulloway, Ph.D., author of Born to Rebel. "It's the roles siblings adopt that lead to differences in behavior," he says. And parents tend to reinforce these roles, whether they realize it or not. Keep reading to learn about personality differences between your only, oldest, youngest, or middle child.

Oldest Child Characteristics

Since firstborns follow their parents' lead, they like taking charge and have oodles of confidence, says Kevin Leman, Ph.D., author of The Birth Order Book: Why You Are the Way You Are. That's because they don't have older siblings to tease them when they learn to tie their shoes or ride a bike.

In addition, adults take them seriously, and that boosts their confidence. So, when parents gush over the oldest sibling's "firsts," it motivates them to achieve. Evidence of this: Dr. Leman recounts a corporate seminar he conducted for CEOs in which 19 of the 20 attendees were firstborns.

It's easy for ambitious firstborns to become perfectionists; after all, they see adults coloring inside the lines and pouring milk without spilling. Your firstborn wants everything just so, Dr. Leman says, and they want to get things right the first time. To this end, they may resist pouring their own milk or coloring on their own because they don't want to make mistakes. Unfortunately, these perfectionist oldest child traits also mean firstborns may have trouble admitting when they're wrong.

It's not difficult to see how firstborns can become so tightly wound: New to their parenting roles, first-time parents can be overprotective and tentative while being strict and demanding, says Dr. Leman. This parenting style can lead to "oldest child syndrome" and the conscientious desire to overachieve.

Tips for parenting your oldest child

  • Lower expectations. Parents tend to view firstborns as role models for younger siblings, which can be a lot of pressure. "Watch for the effects of stress," cautions pediatrician T. Berry Brazelton, M.D., coauthor of Touchpoints 3 to 6: Your Child's Emotional and Behavioral Development (Perseus Publishing). Also, avoid using "should"—as in, "you should've known better."
  • Offer privileges. While you're doling out extra responsibilities to your oldest, grant some privileges, too, like a later bedtime.
  • Ease up on responsibility. "It's easy to put too much responsibility on the firstborn," says Dr. Brazelton. For example, your oldest might volunteer to bring the baby a toy when they're fussy or hand you a diaper, but don't expect their help all the time.

Middle Child Characteristics

Middle-born children are often entirely different than older siblings. "Once a role is filled by the firstborn, the secondborn will seek out a role that's completely the opposite," Dr. Leman says. "Middle child traits are the hardest to categorize, but whatever traits they develop play off the first born," he says. That's because middle child personalities emerge in response to how they perceive the next-oldest sibling in the family. So, for example, if the older sibling is a parent-pleaser, the middle child might rebel to get attention.

In the eyes of the middle child, the oldest siblings reap all the privileges, and the babies get away with everything, so middles learn to negotiate to get what they want. "Middle-borns are the most willing to wheel and deal," Dr. Sulloway says. They are agreeable, diplomatic, and compromising, and handle disappointment well. They have realistic expectations, are the least likely to be spoiled, and tend to be the most independent. Because they often feel left out, they tend to gravitate toward friends outside the family.

Tips for parenting your middle child

  • Offer gratitude. Thank them when they step in to mediate a sibling squabble.
  • Prioritize friends. Respect their need for peers. Create opportunities to meet new friends at the park or on playdates.
  • Have one-on-one time. Firstborns have their parents all to themselves initially, as do lastborns once their other siblings grow up and leave home. But the middle kids always have to share parental attention. So, set aside extra time for your middle child to make them feel special, recommends Dr. Brazelton: "Do it for every child, individually, but especially for that middle child."

Youngest Child Characteristics

Since they are no longer first-time parents, parents tend to let things slide once the last child comes along. As a result, lastborns usually get away with more than their older siblings do, says Dr. Leman. They shoulder less responsibility, so the youngest child tends to be carefree, easygoing, fun-loving, affectionate, and sociable, and they like to make people laugh.

But being the youngest isn't all roses. Because lastborns view their older siblings as bigger, faster, and smarter, they may attempt to differentiate themselves by being more rebellious, says Dr. Sulloway. Dr. Leman, himself the family baby, agrees with this youngest child syndrome: "Lastborns have an 'I'll show them' attitude." And if older siblings baby the baby, lastborns might be spoiled and manipulative.

Tips for parenting your youngest child

  • Let them decide. Lastborns often feel they aren't taken seriously. So, let them make some family decisions—like where to go out for dinner or which video to watch together.
  • Acknowledge their "firsts." When they learn to tie their shoes or pee in the potty, call the relatives as you did with the firstborn. And be sure to make a big deal of their artistic accomplishments, displaying their drawings on the fridge, as you did for their older siblings.
  • Give them some responsibilities. Lastborns can end up with few family duties because they've learned to duck out of work or other family members have dubbed them too "little" to be able to handle things, says Dr. Leman. But, responsibilities help kids feel important, so offer them something simple like putting napkins on the table.

Only Child Characteristics

Because only children spend so much time alone, they're self-entertainers and often tend to be the most creative of all birth orders. In fact, Dr. Leman calls only children "Super Firstborns." Like oldest siblings, they are confident, well-spoken, pay enormous attention to detail, and tend to do well in school. Plus, spending so much time around grown-ups often makes onlies act like "little adults."

Only children have never had to compete for their parents' attention or share toys with their siblings, so they risk developing a self-centered streak. Dr. Leman says they're also used to feeling important and may have a hard time when things don't necessarily go their way. Because their role models are competent adults, onlies are even more susceptible to perfectionism than firstborns.

Tips for parenting your only child

  • Schedule playdates. Since they aren't used to sharing with other kids at home, only children can benefit from playgroups.
  • Make mistakes no big deal. Onlies lean toward perfectionism, so model acceptance of your own mistakes. Remind them that you couldn't cut out a perfect circle at their age, either.
  • Let it slide. Don't seize every opportunity to teach them a better way to do something. For example, if they make the bed with a few wrinkles, don't remake it. You don't want to send the message that they are not measuring up.

What About Twins?

"Twins don't usually follow typical birth order roles," says Nancy Segal, Ph.D., twins expert and author of Indivisible by Two: Lives of Extraordinary Twins (Harvard University Press). "Most parents tend to be very fair and not emphasize order of birth, at least in Western nations," says Dr. Segal. However, when twins are born vaginally, the firstborn is usually bigger, and the secondborn has a greater risk for health problems. In these cases, parents may unconsciously treat the first twin more like a firstborn.

Factors That Affect Birth Order Personalities

"Many things contribute to human behavior," says Dr. Sulloway. "Birth order only explains a small chunk." Some other factors that alter traditional birth order roles include:

  • Sex. Being born first doesn't necessarily guarantee "firstborn" status. For example, in some cultures, a boy may be treated like a firstborn even when he has four older sisters because he's the firstborn male.
  • Age differences. Birth order effects are strongest when siblings are two to four years apart in age. With significant age gaps, siblings might act more like only children or firstborns. On the other hand, siblings separated by fewer than two years are almost like twins. "When sibs are close in age, there's a physical equality," says Dr. Sulloway. It's hard to grab that truck from your younger brother when he's not all that little.
  • Siblings with disabilities. Younger siblings may take on the firstborn role when a child is born with a disability.
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