In 2013, an obese man went to a hospital in Denmark to get his stomach stapled. It was a normal bariatric surgery, with one exception. The man donated a sperm sample a week before the procedure, then a week, after the procedure, then donated a third sample a year after the procedure.
Scientists were determined to prove an interesting hypothesis: if a man's experiences can alter his sperm, and ultimately alter his offspring. This is a controversial idea, because the standard belief about heredity is that parents pass only genes down to their children. Genes that predispose children to factors like obesity, stress, or cancer, or they don't. Whether one's parents were actually obese or anxious does not rewrite the genes.
But, in the past few years, a number of animal experiments have challenged this conventional understanding of heredity. For example, in 2010 Dr. Romaine Barres of the University of Copenhagen fed male rats a high-fat diet then mated them with females. Compared to male rats fed a regular diet, the high-fat rats fathered offspring who tended to gain more weight, develop more fat and have trouble regulating insulin levels.
Eating a high-fat diet was just one factor that could alter a father's offspring. High levels of stress have been thought to affect the offspring, too. Male rats exposed to stressful environments, such as smelling the odor of a fox, will father offspring with a dampened response to stress.
Scientists have taken a close look at sperm to determine the link between a father's experiences and his offspring's biology. Genes are regulated by molecules called epigenetic factors. These molecules can respond to environmental influences and silence or activate certain genes as needed. Some studies have suggested that changes to epigenetic factors can be passed down to offspring.
Dr. Tracy Bale, a neuroscientist at UPenn, examined the sperm of stressed rats and saw unusual levels of epigenetic molecules called microRNAs. Scientists have only started to investigate the epigenetics of fatherhood. The studies have been influential, but not clear-cut.
Dr. Barres investigated the potential link between epigenetic differences of children with obese fathers vs. lean fathers. He collected sperm from ten obese Danish men and thirteen lean ones. They found numerous epigenetic differences, including the molecular caps that are placed on DNA in a process called methylation. He found more than 9,000 genes in which the methylation pattern differed between obese and lean men.
After this finding, they recruited six obese men getting bariatric surgery to see if losing weight changes this pattern. Dr. Barres and his colleagues identified about 4,000 genes that were methylated differently a year after the surgery. These epigenetically altered genes are genes that control behavior such as appetite control. The new study does not prove that these changes have any affect on the father's children. Next, they will study the father's sperm and the pattern of the offspring's blood cells, to get a deeper understanding. To prove this finding, there must be more studies with many more people, such as hundreds, to prove this effect.
I think this study is very interesting, it is something I never thought about before. I definitely have the standard belief about heredity, that genes are only passed on to offspring, not experiences. But after reading this article and thinking about the causes and effects, people always say that addiction "runs in the family." A person would not be addicted to something if they never tried alcohol, or a drug, so wouldn't we say that addiction is inherited by the parent's lifestyle? I don't have the best understanding of addiction or how it comes about, but if someone drinks on a daily basis and feels like they need alcohol, it is accepted by many people that the children can have an addictive personality too. So, why is it hard to believe that if a parent eats uncontrollably, and is ultimately addicted to food, will have the same effect on children just like alcoholism does? I agree that more studies need to be done to prove this, but I believe that a parent's (not just a father's) experiences and habits can be passed down to their offspring after reading this article.