Epigenetics is starting to come into its own and revolutionize our understanding of biology and genetics.
Men, if your grandfather entered puberty during the time of a famine, you are more likely to have a long life. Women, if your grandmother was in the womb during the time of a famine, you are more likely to die unusually young.
We are learning that it isn't only genes that are passed from generation to generation and that genes alone do not account for the diversity in our species and between identical twins. What matters even more is what genes are expressed, or turned on, and when and in what combinations. Things that you do or experience now can affect what gets turned on in your children and grandchildren. Your smoking or eating habits can lead to the cancer of your grandchild that you never even meet. Our behaviors have a bigger influence in the genetic destiny of our offspring than realized - increasing our responsibility for our actions beyond ourselves but also onto future generations to an extent never before imagined.
On the flip side, epigenetics also provides hope: Doctors are learning how, in some cases, to turn some activated genes back off to cure cancers that were hopeless cases before.
See the episode on NOVA.