 Most people have a sibling. In fact, children in the US today are more likely to grow up with a brother or sister than with a father. Now, while a lot of social scientists research the impact of schools and parenting, little attention is given to a relationship that might be even more consequential. So what do we know about siblings, birth order, and why children from one family grow up to have very different personalities? Let's start with our analysis of the tragic story of the two most famous brothers in Western history. Once upon a time, there was a boy named Kane, who received all the love and attention from both of his parents. Growing up, the boy knew only one world, and he himself was at its center. Everyone around him cared only for him and nothing else. All that changed when his mother gave birth to Abel. Kane should have understood that his parents' attention now had to be divided between him and his brother. This was a revelation he wasn't able to accept, and he became increasingly jealous and sometimes even violent against his little brother. Kane, as the firstborn, naturally looked up to his father as his role model. Following convention, the father himself raised the boy with certain expectations. It was therefore especially painful for Kane to see that his father now cared so much for his younger brother. Abel naturally looked up to his brother for guidance. Things were not easy for him either, but unlike Kane, Abel knew no different. As the boys grew up, Kane gained a strong sense of responsibility and, following tradition, took over the family farm. Abel, who was free from any obligation, chose to become a shepherd. Kane envied his younger brother's autonomy because life as a farmer became increasingly difficult. And on the day that the brothers were to make a gift to their father, Kane only brought a few bundles of dry grass. Abel, who did well for himself, brought an entire lamb. When the father thanked Abel for his generosity, Kane felt a deep shame. Overnight, his shame turned to hatred of monstrous proportions, and the next day he killed his own brother. The first big contribution to the field of sibling research came from the Austrian psychiatrist Alfred Adler and his theory of individual psychology. Adler believed that the main motive of human behavior is our desire for power, partly in compensation for our feeling of inferiority. Hence, sibling dynamics play a central role in family life and personality development as we grow up. Adler argued that children who grow up in the same family experience the family differently. In particular, sibling rivalry over family resources influences the development of personality. As a means of reducing competition, siblings differentiate, develop different qualities, and choose different interests. When siblings don't find their niches, their relationship can suffer. The Kellogg brothers hated each other and fought in court over who invented corn flakes. The Darcelers competed in business after one started Adidas, the other founded Puma. But many siblings love each other more than anything. So what do we know about siblings in general? Here are six things science suggests to be true. Firstborn and single children look up to their father or mother as role models. The gap in mental and physical development between them and their parents may be the reason that they have, on average, a higher IQ. Parents tend to give their firstborn more attention and often set higher expectations. If they can't live up to those expectations, they may feel inferior, but on average, they seem to benefit from their position. Younger siblings model their development after their big brothers or sisters. They have a smaller developmental gap to overcome. They may also feel that they have less to prove, but as a result of a lack of parental attention, they develop social anxiety more often. On average, relationships between brothers are more conflicted. Relationships between sisters are more intimate. Siblings spend more time together than they spend with their parents. Younger siblings even twice as much. Children with siblings are physically more active and less often obese. They are often happier too. Some studies suggest that they develop social skills faster than children from only child families, but the research isn't conclusive. Sibling attachment seems to be a strong predictor of well-being, sometimes more important than paternal attachment. This also means that if one is bullying the other, it can affect them for life. One Swedish study of people aged 80 years found that while closeness to friends did little for total life satisfaction, feeling close with a sibling did a lot. For those of you struggling with a difficult sibling, Adler had the following advice. A simple rule in dealing with those who are hard to get along with is to remember that this person is striving to assert his superiority, and you must deal with him from that point of view. This and all other Sprouts videos are licensed under Creative Commons. That means teachers from all around the world can use them in classrooms, online courses, or to start projects. And today, thousands already do. To learn how it works and download this video without ads or background music, check out our website or read the description below. If you want to support our mission and help change education, visit our Patreon. That's patreon.com slash sprouts.