It is common to see someone who is in great shape and attribute that to their genetics. On the flip side, people who are obese claim to be destined to always be obese because it is in their genes. This is one side of the nature versus nurture argument. We are born with a certain set of genes that we inherited from our parents, so we will end up being similar to them. It seems like a done deal. Or, maybe not.
Scientists are discovering that just because two organisms have the same DNA, they don't always have the same appearance or susceptibility to disease. This is even more evident when each organism is placed in a different environment (ie. different location, diet, stresses, social interaction, etc). The term epigenetics has arose from the study of how genes express their phenotypes (physical characteristics) in organisms. Like most biological fields of study, this started with plants and lower organisms, and now is being examined in humans.
What is interesting to me, is that high-intensity strength training may have an effect on the expression of your genes. So, even if you were a pudgy, weak kid, regular exercise training can regulate how some genes are expressed in your body and ultimately give you more control of your body. So, physiological outcomes like sarcopenia (loss of muscle mass with aging) cancer, heart disease, dementia, and depression may be prevented or delayed even if you have a strong family history. Mark of Mark's Daily Apple had an interesting post on epigenetics and depression here.
As I have believed for years, regular exercise training empowers you in ways that non-exercisers will never come to know. Now, with the exciting field of epigenetics , we will discover just how that happens.