It is good genes that make success, and nothing an individual does during his lifetime has any effect whatever upon its genes.
Richard Dawkins, Evolutionary Biologist (1995)
We all know that the genes that make up our DNA control many aspects of our lives, like the shape of our eyes, but what controls our genes? Back in 1995, any respectable scientist would have said "nothing." But today we know about epigenes. The cells of your teeth, eyeballs, skin, and liver all have identical DNA, but different epigenes. These epigenes turn on and off certain genes to get the cell to develop correctly. Genes are the hardware; epigenes the software. Or if you like, genes are the factories, and epigenes are the little guys who decide what the factory will produce.
Epigenes change to meet the situation. If that being is creating eggs or sperm (a girl in the womb or a boy in early puberty), the imprint of those epigenes are recorded for the following generation. And here's the exciting part, certain epigenes, like the ones controlling for body weight CAN be affected by environment, so that the corresponding epigene will not "turn on" an undesired gene.