Last week we stumbled across a documentary on t.v. about epigenetics- I'm far from understanding all the molecular biology aspects- but the gist of it is that environmental factors can affect your genes in such a way so that they have an effect on your grandchildren. Which seems far fetched until you really think about it. In the show they were talking about the eating habits of grandparents at the time that they were producing sperm or eggs, and how that caused the quality of their sperm or eggs to be altered which causes the effect in their children (they were linking nutritional defences to diabetes in later generations)
In the Hundered Year Lie by Randall Fitzgerald- he's talking about the same type of thing except he's focusing on chemical exposure and their lasting effect on the human species. Any chemicals that I was exposed to while pregnant with N will affect her- but also since she is a girl- any chemical I was exposed to while pregnant will affect her eggs because the exposure occurred while they were being formed, and therefore it will affect my grandchildren too. For men the prime time for exposure is before puberty, when they develop sperm.
The really scary thing that the documentary pointed out was that the changes that they noticed in the offspring of lab animals who were exposed to chemicals weren't limited to one generation- the effects were passed on in different ways, indefinitely. Which means any exposure to chemicals is not only affecting us, but our entire line of descendants. Frightening stuff, it kind of puts a new impact on our attitude towards drugs and synthetics, because in a way we don't really own our genes- we just lease them. I know lots of people who expose themselvs to harmful things (myself included) with the mind-set that they're only hurting themselves, but apparantly that just isn't so.