Just wow. Go watch it.
Because I know some of you won't (shame on you), there is new-ish research showing that the influence caused by environmental factors can be passed down genetically. For example, if your grandmother was exposed to high levels of a toxin, you may possibly exhibit the same ill effects although you never sniffed that toxin in your life! Or if you experienced a traumatic, stressful event that left you with symptoms of post traumatic stress disorder, your grandchildren could exhibit the same symptoms although never experiencing the event you did. These environmental factors occur and get locked into the jumble of genetics that makes you "you".
They explain it SO much better in the documentary (probably because they actually GET it).