Studies on human twins and families over generations conclude that almost all traits are, at least in part, influenced by genetics. (seeker.com)
The first two types discussed were based on studies from human twins, whereas the third type was formulated based on research using mice. (personalityresearch.org)
More evidence that the bacteria that live within us may be partly responsible for whether we're fat or thin: In a novel experiment at Washington University, researchers implanted bacteria from pairs of human twins — one obese and the other lean in each pair — into the intestines of genetically identical mice bred in a sterile environment so that their guts contained no microbial life. (discovermagazine.com)