What to Know About Birth Order

Medically Reviewed by Dan Brennan, MD on July 12, 2023
4 min read

Birth order has been used to predict success, prosperity, jobs, and more. But does it really affect who you are and what you do in life? Here's a closer look at the truth and science behind birth order.

A researcher named Alfred Adler developed birth order theory in the 20th century. The theory claims that the order in which a child is born shapes their development and personality. Adler also claimed that family, community, and social aspects play a major role in shaping a child’s personality.

Today, many psychologists believe that where you fall in your family’s birth order has a major impact on your personality development.

Oldest child. If you're the firstborn child, you have your parents all to yourself for a period of time. Because it’s your parents’ first time being parents, they tend to dole out attention to you. They’re also extra careful when it comes to all aspects of child rearing — from bumps and bruises to early education. Eldest children benefit from all this attention. 

Your parents might expect a lot from you if you're the oldest, especially as other children are born into your family. Your parents might seem stricter with you, and often expect you to set an example for your younger siblings and show responsibility.

Studies show if you're the eldest child, you tend to demonstrate leadership skills. Maybe you're a leader in the workplace already, or rising to the top of your industry.‌

Middle child. It’s a stereotype that if you're a middle child you're a peacekeeper, but there seems to be a grain of truth behind the saying. Because you lack the title of being the oldest or the youngest, you seek to carve out a niche for yourself in the family dynamic. You tend to enjoy negotiation and compromise. You can often relate to people of different ages with ease.

You can be competitive with your older sibling — maybe by breaking their sports records, becoming more fluent in a language, or getting better grades. Or you might behave more rebelliously.

Youngest child. As the baby of the family, you tend to take one of two paths when developing your personality, according to Adler. The first path is a clear journey to success, where you try to excel in every way, often becoming the go-to person in the family. Youngest children can also become avoidant if they lack the confidence or drive to excel.

You might have freedoms your older siblings don't have. As your parents’ rules become more relaxed, your parents can be more hands-off with you. You're usually assured of your place in the family and can be very creative, rebellious, and outgoing.

Only child. If you're an only child, you've been surrounded by adults since birth. That’s not to say you weren’t socialized with other children through kindergarten, the playground, or school. But during your time at home you socialized with parents and other adults, mimicking their behaviors and becoming "small people".

Your parents might be overprotective of you, leading you to become dependent on your parents for support. You aren’t used to sharing clothes, space, or parental attention with siblings. This can make you intelligent and creative, but also stubborn and set in your ways.

Some theories claim that firstborns are more intelligent and have a higher IQ than later-borns. But the most recent studies show that firstborns only hold a 1-point IQ advantage on average over their siblings. Social factors could be to blame for this idea. 

Another study shows that firstborns might benefit from being surrounded by adults during their first years. They absorb the way adults talk, while later-borns are more exposed to the less-developed ways their siblings speak. 

The same study found that firstborns often take a leadership and teaching role to their younger siblings. Some theories say tutoring improves the intelligence of the tutor — in this case, the older sibling. 

Some people think birth order affects health. Studies suggest if you’re the oldest, you're more likely to have a lower birth weight than your siblings. 

Later-born children have an increased risk of hospitalization due to avoidable accidents. This could relate to a lack of parental attention in a large family. Younger siblings may struggle with mental health during puberty and young adulthood, and are more likely to be admitted to the hospital for reasons relating to alcohol. 

Overall, researchers found most birth order differences are due to where your parents choose to spend their time and resources. 

Birth order is a complex subject. There isn’t a “one-size-fits-all” for every family. Different factors affect social family dynamics, and results differ from child to child and family to family.

Some other factors that influence birth order include:

  • Parental attitudes and culture. In some cultures, even if a boy is born after four girls, he may still be treated as the oldest.
  • Age difference. Adler notes that if children have an age difference of more than three years, subgroups with different dynamics may form. Most experts agree, but place the age gap at five years.
  • Twins. Most twins get special attention from parents, so experts say these rules don’t necessarily apply.
  • Confidence. A child’s opinion of themselves determines their outlook and attitude. While birth order helps shape their personality, it’s not the only factor.