FIRSTBORN children are more likely to achieve greatness, but this may come at the cost of a less trusting, uncooperative disposition.
We know that firstborns are generally smarter than their younger siblings and , while . To see if trust in adults might also be affected by birth order, Alexandre Courtiol at the Institute of Evolutionary Sciences in Montpellier, France, paired 510 students with anonymous partners to play a finance-based game. Both players were given 30 monetary units and told that whatever they had left at the end of the game would be converted into real cash. Player A was told to give any sum of money to player B, with the knowledge that this would be tripled for player B鈥檚 pot. Player B then had the option of giving any sum of money back to player A.
The selfish decision would have been for neither player to give any money away, but less than 1 in 10 participants played this way. The more money player A gave away, the more trusting they were judged to be and the more money player B tended to return, showing reciprocity.
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On average, eldest siblings gave 25 per cent less 鈥渕oney鈥� than non-firstborns or only children, whether they were in role A or B. Courtiol interprets this as meaning firstborns were 25 per cent less trusting and reciprocating (Animal Behaviour, ).
鈥淓ldest siblings gave away 25 per cent less money than non-firstborns or only children鈥�
He suggests there may be a limited amount of energy that people can invest in cooperative alliances, 鈥渟o it may be that the firstborn cooperates less outside the family because they cooperate more within it鈥�.
A conflicting explanation is that within their families, firstborns actually cooperate less in an attempt to maintain their initial monopoly on parental care, and interact with others in the same way as adults. The study confirms that birth order can have significant and lasting effects on personality and behaviour outside the family, says Frank Sulloway, an evolutionary psychologist at the University of California, Berkeley.
