But often the elder ones are more idealistic whereas the junior siblings tend to be practical-reason being that while the first borns have to negotiate with ELDERS (since no other peers are available in a Nuclear Family)and PARENTS for their demands,the second (and third and soon) children can easily learn to negotiate with their elder brother/sister who may be 2-4 years senior only ,and Physically much less formidable.
This builds the negotiating and social skills of the non firsts,while the first borns sometimes perform better in highly intellectual or intuitive ,or even even quirky,environments.
Being a first born,my own observation is that it is the (situational )positive expectation by the family environment that helps them better in their areas.That also explains why those second borns whose elders died ,also improved performance.
In essence everything ,putting aside Karma theory for a moment,is the result of social programming ,including the "stroking",that the child undergoes...remember Eric Berne's "Transactional Analysis"?