[tokenadult]

50% of it is determined by birt or genetics.

But this is a misinterpretation of what broad heritability shows.

http://news.ycombinator.com/item?id=838534

In other words, it may be that there are environmental interventions that can HUGELY influence happiness that just haven't been tried yet. Better understanding of the development of happiness over the course of life, a line of research evidently being pursued by your professor, may eventually show what some of those interventions are.

[jamesbressi]

Agreed. I believe that "50% of it" is UN-determined. Genetics undoubtedly play a role, but environment (development, interventions, etc.) dually play a role.

The problem is that environment and its interventions can be a difficult variable to tie down in studies. Good call.