Nine ways your sibling will affect your adult life, according to science

Anyone who's borrowed their big sister's make-up or helped out a younger sibling with their homework knows that our brothers and sisters are a big influence in shaping the person we grow up to be.

Now new research shows that our relationships with our siblings are more important in determining who we become than parental support, IQ, people skills and our own work ethic.

Whether or not you have a sibling and where you come in the pecking order can have a great influence on who you are, from the likelihood you'll be gay to career success and how much sex you have.

Here are some of the most mind-blowing ways sibling relationships affect us more than our shared genes and home environment, according to Dr Jonathan Caspi, an expert in child and family studies:

1. Siblings strive to be different from each other

For every set of Williams sisters there are thousands more sibling sets that actively try to follow different paths, and the closer you are in age the more likely that is.

2. Your parents were lying: they really do treat you differently

There is now lots of empirical evidence that parents allocate their emotional and material resources differently between their children according to their needs and temperaments, which is bad news for disfavoured children. Research even suggests that families with limited resources will invest more in one child that they think has the most potential to do well.

3. Older brothers can make you gay

No really: it's called the Fraternal Birth-Order Effect. For each son a woman has, the next one is between 28-48 per cent more likely to be gay. You'd need to have 10 big brothers before the probability of being gay passed the 50 per cent mark - but it's still estimated that one in seven gay men can attribute their sexuality to this fact.

4.Older siblings are usually smarter

On average older siblings have three more IQ points than their little brothers and sisters, supposedly because they get their parents' undivided attention in the crucial infant learning years. Each subsequent child logically halves this attention.

5. Firstborns tend to be more rule-abiding and academically focused, while younger siblings are risk-takers

According to Caspi siblings use strategies to win their parents' time and resources which are influenced by birth order in order to attract parental investment without openly fighting for it.

6. Older sisters make boys less competitive

As such, growing up with a same-sex sibling increases your chances of direct competition, which can be both healthy and unhealthy.

7. If your parents compare you a lot it the psychological effect stays with you in adult life

One study found that people who compared a lot to their siblings are far more anxious about economic success, and that individuals who earn more than their siblings report greater life satisfaction.

8. Younger siblings are better at attracting members of the opposite sex

Having an older sibling of the opposite sex is a boon for your social life. One study found that in a speed dating environment men with older sisters were significantly more conversationally adept, and women with older brothers were likely to strike up a conversation with a man and smiled more than other women.

9. Being close to your brothers and sisters is good for your mental health and your wallet

Not only do close sibling relationships help protect you against childhood shocks like divorce and domestic violence, they actively encourage you on towards success. People with strong brotherly and sisterly bonds report greater life satisfaction, and being happy is linked to economic success.

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