(Not so) Suprisingly, DNA on its own will not completely determine an individual. While this is sometimes used as a cheap "evil twin" plot device, it holds true because of a molecular body known as the epigenome. It governs expressivity of the underlying coding and is itself affected by environmental factors such as stress, drug exposure, and diet. While not to the extreme of effecting morality, this potentially explains why one identical twin might develop a condition like diabetes or asthma while the other does not. What is most interesting about the field of Epigenetics is that environmental factors can effect subsequent generations long before they were ever concieved, which is what researchers in Sweden looked to examine in their northernmost county of Norbotten.During the timeline that was being examined, Norbotten had:
- Extreme isolation from the rest of Sweden - meaning less genetic variations in the population.
- Agricultural Independence - Locals eating locally grown food, meaning no sudden surge in food quantity thanks to outside influence.
- Distinct time periods of extreme famine and abundance - making it easier to point out which individuals had experienced what type of consequent eating habits through life.
Adults who had experienced even one winters worth of overeating as children were shown to produce offspring with a lower lifespan than their famine-enduring counterparts. Depending on the constraints on other variations possible, the difference in longevity ranged from 6 to a whopping 32 years! And it's not just the overeating of today that can cause the problems of future generations. Epigeneticists have been looking into the smoking and drinking habits of adults when they were in their youth, too. For example, one study saw an increase in a son's BMI depending on their father's smoking habit before and during his teen years.
TL;DR - The cheeseburger and cigarette of today can plummet the life expectancy of your kids tomorrow.
Source: Time Magazine