Your Opinion Required: Firstborn children are 25% less trusting and reciprocating

Popular (mis)conceptions say that 'First-born children are more likely to achieve greatness', but recent research claims that if this is true, then it comes at a price. Scientists say that the only-child and the first-born child is more likely to be less trusting, and have a less generous or a less cooperative disposition.

Previous Research
Previous studies would lead us to believe that firstborns are generally smarter than their younger siblings and perhaps more likely to become leaders, while younger brood-members tend to be more rebellious. It would be interesting to know if you have found this to be proven, in the real world.

Recent Research
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.

It is a standard game used to shows a umber of things:

• the level of trust a person has in other people,
  
• their willingness to take part in collaborative and cooperative behaviour and
  
• the level of risk they are willing to take.

It can also be used to try and understand the level of 'greed' a person has but that's a much more intangible trait that needs other coroborating data.

The Rules of the 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's pot. Player B then had the option of giving any sum of money back to player A.

The Results
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.

Summary
On average, an only-child or the eldest of a number of sibling, gave 25 per cent less "money" 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, DOI: 10.1016/j.anbehav.2009.09.016).