Firstborn donors...

Oldest siblings give away 25 per cent less money than non firstborns or only children.. !
A study  by Alexandre Courtiol at the Institute of Evolutionary Sciences, Montpellier, France has indicated the finding above. The study paired 510 students with anonymous partners to play a finance-based game though with real cash rewards at the end. The game included multiple strategies of varying selfishness relating to degrees of trust and the interpretation was that firstborns are 25 per cent less trusting and recriprocating..  Explanation  is that there may be a limited amount of energy that people can invest in cooperative alliances so it may be that the firstborn cooperates less outside the family because they cooperate  more within it.  An alternative theory is that it may be that within families, firsbourns actually cooperate less in an attempt to maintain their initial monopoly on parental care, and interact with others in the same way as adults.