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How Your Siblings Affect Your Success According to Science

How Your Siblings Affect Your Success According to Science
Published June 18, 2015 by Dr. Jonathan Caspi
It is an odd thought that our sibling relationships may be at the center of what makes us who we become. We may prefer to say that our success is due to parental support, social connections, and particularly our personal attributes, including our own hard work and intelligence. However, it is our siblings that may be the most influential in this regard. They shape our sense of selves, our identities, our skill sets, and ultimately our life choices. Simply put, if you had a different sibling you would be a different person.

When Mike Thompson was only four years old he could do something very few other children that age could; ride a two-wheel bike without training wheels. This was not the wobbly riding of a novice. He rode one-handed, did jumps, and attempted tricks. He was a bike-riding phenom and people noticed. Neighbors, family, the letter carrier, all commented on how incredibly talented the young boy was. “He’s going to be in the X-Games someday,” said the amazed 13-year-old boy living next door.

While Mike spent every opportunity riding around on the front lawn of their house, his older brother Ben, age six, sat on the front steps reading. Ben had been an early reader and got lost in story books. But Ben had never attempted to ride a bike and when asked, he said he had no interest. Who could blame him? His first attempts would be awkward and clumsy, and involve falling in front of a potent audience, that not only included his family, but all the other observers that commented on his younger brother’s talents. He would immediately feel like a failure and pale in comparison. There was little payoff in trying to learn to ride a bicycle. He would always be number two.

If you had a different sibling, you would be a different person.

Ben and Mike are now adults. As you might expect, Mike spent much of his life in sports, hanging with other athletes, and becoming indoctrinated into its accompanying culture. In middle school, high school, and college, the athletes are often the high status kids. These experiences shaped Mike’s identity and self-esteem. As an adult he is social, confident, and a successful Wall Street executive; a position he got due to college sports connections. Ben, by comparison, spent much of his time with kids of like interests; the more scholarly, or “nerdy,” types. He was exposed to an entirely different circle of friends with a unique social culture. Ben grew up seeing himself as smart, curious, introspective, and is now a successful university professor.

Based upon the expression of their talents early in life—and how they compared to their sibling’s talents—everything else in their life changed. These sibling experiences were central to each’s success.

In fact, all their life choices were influenced by who they had as siblings. Had Ben grown up with a sibling that was less athletic, who would he be? Perhaps he would have ridden his bike, become interested in sports, and focused less on academic pursuits. Who we have as siblings influences our identities, aspirations, relationships, and interests. Consequently, our siblings have great influence in our life choices and success. However, how much of this occurs is largely gradual, and thus invisible. It is unlikely that Michael or Ben would credit each other for their success.

It’s rare enough for a family to have one child achieve a high level of success, so when multiple siblings achieve success it is fairly remarkable. Family economists, by measuring sibling pairs, have reported that only about half share the same level of economic and educational success. Of this group, most are not at the high-end of wage earners or education. This finding also suggests that there is disparity between half of all sibling sets. For every Williams sisters, Bush brothers, or Gyllenhaal siblings, there are many more families in which only one, or neither, child achieves high success.

Only about half of siblings share the same level of economic and educational success.

There are other factors that contribute to success, and no explanation of achievement is complete without the argument that working hard is the primary cause. While it is true that perseverance and dedication to tasks are both predictive of success, it is not true that all people who work hard experience success. There are also countless examples of those who did not need to work hard to achieve high levels of accomplishment. Hard work is important for some and not for others. The trait of “hard worker” may be a combination of genetic temperament, family expectations, environmental opportunities, and other factors. From a sibling perspective, the “hard worker” label and trait may have emerged and been fortified in the context of having a “lazy” brother or sister via parental comparisons.

An additional important point; not all success is economic. Success in careers does not mean success in marriage, friendships, or as parents. The factors that promote financial and educational success may not necessarily promote healthy marriages, parenting, or friendships.

So why do some individuals enjoy success while others do not? In recent years, a growing and impressive body of research has been demonstrating that siblings are highly influential in human development, perhaps even more so than parents or peers. Although the research on how siblings directly contribute to individual success is limited, there are some compelling considerations that can be derived from research findings. The following five elements are the ways in which our siblings affect our own success.

1. Genetics

Genes are certainly important, but do not tell the whole story. If genes were to thank for talent or success, you would think that more families would have multiple offspring rather than single-offspring successes. While one can name many examples of sibling sports stars, such as the Williams sisters or the Manning brothers, most stars do not have sibling who is also a professional athlete. To that point, Michael Jordan certainly possessed the genetic constitution to become one of the greatest basketball players of all time. He had the height, coordination, and physique required for such success. If success were purely explained by genes, why were none of his siblings also professional athletes? Research has shown that siblings, despite shared genetics, are quite different from each other.

Genes are certainly important, but do not tell the whole story.

In fact, siblings are as different from each other on personality and psychological adjustment (e.g., anxiety, depression) tests as complete strangers are, despite sharing genes and environment (more on that shortly). Why are siblings so different? It seems that growing up with each other generates difference (as in the case of Michael and Ben from earlier in this piece), who were each successful in very different areas. Each pursued trajectories that made sense given their genetic constitutions. If we do not possess the build or temperament for an endeavor, success is less likely.

2. Environment

As in the case of genetics, siblings also share environments growing up. They live in the same homes, attend the same schools, experience the same cultural and family traditions, and so on.

Again, you might assume the same environment would produce the same level of success across all inhabitants, so what is it about the environment that contributes to differences in siblings?

First, researchers have found that siblings actively strive to be different from each other, particularly if they are close in age.

Second, there is abundant empirical evidence that parents treat each of their children uniquely, and allocate resources differently. Contrary to the often-heard claims by parents that they treat their children the same, they do not. Children have different individual needs, temperaments, and interests; parents treat their children otherwise as a matter of pragmatics and emotional investment. These disparities are often loaded. Research has fairly consistently [pdf] demonstrated that parental differential treatment is linked to individual problems for disfavored children, and to poorer sibling relationships, which continues into adulthood. Research has also suggested that in families with limited resources parents will sometimes invest more in the one child that seems to possess the most potential.

There is abundant empirical evidence that parents treat each of their children uniquely.

Third, siblings use distinctive strategies for allocating resources, which seem to be influenced by birth order. There is research evidence that siblings select different “niches” to increase parental investment while avoiding direct competition. Firstborns tend to be more rule-abiding and academically focused (particularly firstborn girls), whereas laterborns tend to be more risk-taking. Like Ben and Michael, siblings typically select different areas of expertise in order to distinguish themselves and earn parental investment without having to fight it out.

Fourth, parents value niches differently. A parent may be excited by a child’s interest in sports but not in the arts. Although research on niche availability is non-existent, I have argued that parents who limit niche possibilities (e.g., “all my children must play football”) are more likely to have children compete directly and potentially succeed in the same endeavor (or have one drop out entirely), whereas parents who support a wide range of interests are more likely to see diversification and successes in different areas.

Fifth, families also live in environments that either promote or inhibit success with particular endeavors. Individuals who grew up in households close to golf courses are more likely to excel in that sport than those from urban environments. There are cultural, religious and gender expectations that can support or limit success. Culture influences children’s available extra-curricular activities. There is also the element of time and place in providing opportunity for success, as Malcolm Gladwell argued in his book Outliers. Offspring that graduate college and seek jobs during economic upturns have more opportunities to become employed in economically rewarding situations than siblings from the same family who enter the market during economic recessions.

Finally, families that hold social positions and offer unearned privileges to their children are more likely to produce multiple offspring success. Success is more likely in families that are wealthy, white, educated, and well-connected.

It is clear that environment matters, but it alone does not tell the whole story either.

3. Competition

Sibling competition increases skill sets and is an ingredient of shared sibling success. Individuals do not improve without engaging in competition and siblings represent an early, long-term, and potent relationship. Competition teaches you about your limits, about losing and getting up again, about working hard in the face of adversity, to be creative, and about winning and losing. It is hard to imagine that the Williams sisters or Manning brothers would have been as skilled at their sports without having competed against each other since childhood. Each competition offered opportunities to try out new techniques in order to raise the bar and best the other. Competition, however, can be both beneficial and damaging.

Competition can be both beneficial and damaging.

For both siblings to be successful within the same endeavor, the competition has to be well-intentioned and not with the aim of psychologically injuring the other. Interestingly, same-sex combinations may increase competition, whereas cross-sex may lessen it. A recent study reported that having an older sister was linked to lower male preference to be competitive. As such, growing up with a same-sex sibling may increase competition and opportunities for success.

4. Comparison

In no other relationship are individuals compared as much as siblings. Parents and siblings often describe themselves in terms of opposites, and these comparisons might be exaggerated. Assessments start even before the second child enters the world. A pregnant mother may feel her future child actively kicking and say, “This one is more energetic than our first born.” The siblings’ personalities are already being compared and being used to define them as different. Throughout life, siblings use each other as reference points for success.  One study even reported that individuals who were perceived to make more money than their siblings reported greater life satisfaction. Experts have long suggested that active parental comparison can be problematic, particularly if it casts one child at a disadvantage, such as carrying the label of the “bad one.” A recent study has reported that siblings who are frequently compared by parents have more anxiety about their economic success in adulthood. Comparison results in winners and losers, with one being more motivated and the other feeling diminished.

Throughout life, siblings use each other as reference points for success.

Children and adults pay close attention to comparisons and labels. Labels, such as the “good one” and the “bad one,” or the “overemotional one” and the “stoic one,” reinforce personality differences in invisible ways. For example, consider two siblings described by their parents and others as “serious” and “silly.” The more ridiculous the silly one behaves, the more serious the other appears by comparison. These labels are often potent and lead individuals to make different life choices.

To promote success for all of their offspring, parents should avoid making comparisons, and instead teach the children how to compete to achieve personal success while supporting each other. That is, low parental comparison should increase the chances of multiple offspring from the same family becoming successful.

5. Sibling Closeness

Sibling support has emerged in research as particularly beneficial. It has been shown to buffer children from the harmful effects of circumstances such as divorce, domestic violence, and substance abuse. Close siblings encourage and provide resources for success. Positive siblings view competition as friendly and bonding, whereas negative sibling relationships experience competition as antagonistic and aimed at diminishing the other. A fairly recent and most interesting research study suggests happy people are more likely to experience economic success. It seems that not only does money buy happiness (up to a point), but evidence suggests that happiness also buys money. Sibling closeness is associated with increased life satisfaction, an important ingredient in economic success.


The more we know about our sibling relationships and how they influence us, the better we can make informed life choices that promote success. Understanding that one’s internalized sense of self as a “low achiever” was heavily influenced by comparisons to a high achieving sibling, allows the individual to reconsider and evaluate their own actual abilities. For example, Darlene, the youngest of four siblings, graduated from Johns Hopkins University, one of the top educational institutions in the world. Her three older brothers all attended Harvard University and mercilessly teased her about being “dumb.” Darlene internalized this label and sense of self and avoided taking jobs that she thought she was not smart enough to handle, although she clearly was. Reflecting upon her sibling experiences, she acknowledged that it was only with them that she felt unintelligent and that she may indeed be capable of more than she was attempting. With this knowledge now in hand, she landed a challenging but high paying job as a biochemist for a pharmaceutical company and has quickly moved up the ranks.

The more we know about our sibling relationships and how they influence us, the better we can make informed life choices that promote success.

In sum, positive sibling relationships are beneficial in many ways including promoting physical, mental, and relational health. When relationships are positive, competition is healthy and promotes success. Take time to build positivity into your own and your children’s sibling relationships. This can be done by minimizing comparisons, openly talking about distribution of resources and equity, insuring that competition is not meant to diminish the other, creating opportunities for sibling closeness, support and bonding, and identifying endeavors in which one has the best biological fit for success.

How about you?

How have your siblings affected your success?

More about Dr. Jonathan Caspi

Dr. Jonathan Caspi is an internationally recognized expert on siblings and Professor at Montclair State University. He has published three books, multiple academic articles, and has appeared on WNPR, The New York Times, Huffington Post, Wall Street Journal, and many others. His private practice has offices in Montclair and Hazlet, New Jersey. 

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