Does Birth Order Affect Twins?

Twins eating berries

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One of the first questions that people often ask twins is, "Who was born first?" If you have twins, you may wonder how or if their birth order affects them. 

Understanding Birth Order

There has always been a lot of interest in the study of birth order and its impact on society. Certainly, throughout history, there have been occasions when determining a child's placement in the family was of utmost importance. The birthright of firstborns meant an opportunity to inherit family fortunes, even entire kingdoms, along with the burden of responsibility for the remaining family members.

Scientists have done some interesting studies to evaluate the role of birth order in the development of personality. Some studies have theorized that first-born children have higher IQs, while lastborns tend to be more relaxed and irresponsible. However, a more recent broad study concluded that birth order doesn't have any lasting effect on personality, though it does seem to influence intelligence, and another paper laments the persistence of birth order as a "zombie theory."

Adlerian Birth Order Characteristics

Psychologist Alfred Adler, a contemporary of Sigmund Freud, defined a set of characteristics to describe how a child's position within the family would actualize in their personality. The table below presents a simplified version of his theories adapted from the Adler Institute website:

Position Family Situation Characteristics
Oldest Dethroned by next child. Has to learn to share. Parental expectations are usually very high. Often given responsibility and expected to set an example. May become authoritarian or strict. Feels power is his right. Can become helpful if encouraged.
Second Has a pacesetter, always someone ahead. Is more competitive, wants to overtake older child. May become a rebel or try to outdo everyone. Competition can deteriorate into a rivalry.
Middle Is "sandwiched" in. May feel squeezed out of a position of privilege and significance. Even-tempered, "take it or leave it" attitude. May have trouble finding a place or become a fighter of injustice.
Youngest Has many mothers and fathers in older children. Never dethroned. Wants to be bigger than the others. Can stay the "baby." Frequently spoiled.

Birth Order and Twins

Birth order for twins isn't necessarily preordained, either. The babies' order of birth is determined by their position in the womb, which can change throughout pregnancy. In some cases, which baby is born first depends on how the mother delivers; the order might be switched if the mother had a Cesarean section rather than vaginal delivery.

So how do you explain the manifestation of birth order characteristics in the personalities of individual multiples? Certainly, there are many examples of twin sets where the firstborn twin is a dominant leader and the secondborn is a subdued follower.

What the Experts Say

Unfortunately, there isn't a lot of specific research available on this subject. However, many birth order experts agree that twins tend to organize themselves according to their overall place within the family. For example, if they have one older sibling, they will both exhibit characteristics of a second born. If they are the oldest, they will adopt some traits of firstborns. 

Twins often exchange dominance throughout their lives, and in that sense may alternate between birth order categories.

Aside from inherent personality traits, the impact of birth order in multiples is likely more often one of perception rather than reality, especially in light of recent studies. Parents of multiples, as well as society, apply behavioral expectations based on traditional birth order characteristics; in reaction, the individual children behave in fulfillment of those expectations.

Self-Fulfilling Prophecy

For example, a mother may reason, "Oh, Twin A was born first. She is always first to do everything. She was the first to crawl, and she'll be the first to walk also!" She expects her firstborn twin daughter to walk before her sister and spends more time coaching and encouraging this daughter in this skill.

In reaction to her self-fulfilling prophecy, Twin A naturally walks first. As the twins grow up, their parents expect their "firstborn" to look out for her "younger" sister, establishing Twin A in the dominant role in the relationship, and galvanizing her personality traits in the mold of an elder child.


Parents of multiples have a vital responsibility to foster their children's individual personalities outside of the realm of birth order. To accomplish this, they can do the following:

  • Adopt a consistent, neutral set of expectations that will allow each child to fulfill his or her inherent personality
  • Avoid birth order stereotypes
  • Downplay the significance of birth order; if necessary, choose not to identify the multiples' birth order
  • Discourage others, including extended family, teachers, and curious strangers, from overemphasizing birth order importance
3 Sources
Verywell Family uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Damian RI, Roberts BW. Settling the Debate on Birth Order and PersonalityProceedings of the National Academy of Sciences of the United States of America. National Academy of Sciences. November 17, 2015:112(46):14119-14120. doi:10.1073/pnas.1519064112

  2. Rohrer JM, Egloff B, Schmukle SC. Examining the Effects of Birth Order on PersonalityProceedings of the National Academy of Sciences of the United States of America. National Academy of Sciences. November 17, 2015:112(46):14224–14229. doi:10.1073/pnas.1506451112

  3. Stein HT. Adlerian Overview of Birth Characteristics.

By Pamela Prindle Fierro
 Pamela Prindle Fierro is the author of several parenting books and the mother of twin girls.