A new study claims to have found the specific gene that determines a toddler's willingness to share. Oddly, it's the same gene that's been called the ADHD gene, the bully gene, the brat gene, the drinking gene, and the slut gene. David Dobbs explains how this can be:
[The] long-dominant risk-gene hypothesis, generated first in the mid-1990s, asserts that certain heavily studied gene variants, most of which affect neurochemistry, create higher risk of mood or behavior problems in people who weather rough childhoods. By offering an explanation of why some people are more vulnerable to life’s troubles than others, the risk-gene hypothesis became one of the most influential ideas in behavioral science and a prime model of how genes interact with environment to affect mood or behavior.
This new hypothesis, however, the plasticity hypothesis, acknowledges those genes magnify vulnerability in people with rough starts — but adds that they also create greater strength and happiness in people who don’t suffer troubled childhoods. … The so-called risk genes, in short, don’t just create risk or vulnerability; they make you more attuned and reactive to your environment, whether bad or good.
The Dish 