Ghosts in Your Genes
Can the food your grandparents ate affect you? What about years of smoking one of your great-grandparents engaged in, and ended, decades before your parents were even born? These are some of the questions that build the basis of epigenetics: the idea that the effects of the environment on our genes might actually cause changes within one to two generations, rather than through millions of years of natural selection.
Of course, don't shrug off Darwin just yet. Epigenetics just suggests that perhaps nurture has more of an influence on our nature than we ever suspected. According to these principles, the choices you make and situations you endure today might effect the gene structure of your potential grandchildren!
Time has a great article on the basics of epigenetics, with even more info courtesy of NOVA, who has constructed a companion site for their incredibly creepy yet fascinating series "The Ghost in Your Genes" (which can be found various places online).