>"Science has determined that less than 25% of a person’s lifespan is determined by genes."<p>What does that <i>mean</i>? With a change of just 5% of a person's genes, they'd have been born a rat and died within a lifespan that differed from the average human by far more than just 5%. For that matter <i>wheat</i> shares about 50% of its genes with humanity.<p>I know it would be possible to make 5% alterations in one's food intake that would kill them instantly, so this isn't an argument for genetic determinism. The question is what does "X% of someone's Y comes from genes" mean when it's reported like this?