A man’s weight can affect the information carried by his sperm
A previously discredited evolutionary theory, called Lamarckism, is being revived thanks to a new understanding of heredity called “epigenetic inheritance”.
In 1809, the French evolutionist Jean-Baptiste Lamarck put forward the theory that acquired traits could be transmitted to the next generation. His theory implies that our health is determined by the chosen lifestyle of our ancestors, long before our own existence. And our latest research adds to the credibility of this long-neglected theory.
Since Lamarck proposed his theory, the transmission of acquired traits has been demonstrated in plants and insects. The phenomenon was thought to be restricted to these species but in 2005, a study of inhabitants from a remote village in northern Sweden provided evidence that the theory could be extended to humans.
The study showed that inhabitants were less prone to developing cardiometabolic diseases, such as type 2 diabetes, if their respective grandparent of the same sex (that is, grandfathers for men and grandmothers for women) was relatively undernourished in his or her early life.
The study implied that the eating pattern of parents, long before conception, may affect the developmental message contained in their gametes (sperm or egg) and influence the health of the following generations.
The message is carried in sperm
In our study, we wanted to know whether nutritional status could change the heritable information contained in gametes.
We focused on sperm rather than eggs because it is easier to collect. We collected sperm from 13 lean and ten obese Danish men and compared their epigenetic imprint (chemical tags to the genome that change the expression of genes without changing the DNA code itself).
We found that numerous epigenetic marks were changed in the sperm of obese men and, most strikingly, they were close to the genes crucial for brain development and the regulation of appetite.
In a second group of six obese men undergoing bariatric surgery (surgery to reduce the size of the stomach), we compared sperm from patients before, one week after and one year after the surgery. At the one-year follow-up visit, the men had lost 30kg, on average, and their metabolic profile had dramatically improved.
When we analysed their sperm, we found that the distribution of the epigenetic tags on genes controlling the regulation of appetite was dramatically remodelled. In other words, weight loss did not change the person’s DNA but it did redistribute the epigenetic marks in the genome specialised in “appetite control”.
Notably, this remodelling of the epigenetic fingerprint occurred on the gene encoding the melanocortin receptor, which senses a key hormone in the regulation of hunger and satiety. So we concluded that sperm from obese men contain specific, and potentially heritable, epigenetic information that could change eating behaviour in offspring.
These findings reinforce the idea that environmental factors change epigenetic information contained in our gametes and could affect the eating behaviour and obesity risk of our children. Although the sample size was small, the statistical significance was strong.
The history of my son’s ancestors
A personal note related to this: the day after my son was born, as I was holding him in my arms, I could not help myself from thinking about his biological inheritance. Almost a hundred years ago, in February 1916, his great-grandfather was lunging, starving, in the hell of the battlefield of Verdun in the north-east of France.
My son’s ancestor experienced famines during the world wars. And, unlike hundreds of thousand of other young soldiers, he survived the war, returned to his small village in the south of France and eventually established his bloodline.
Did the various famines of the past century have an effect on his biology? Also, had the increase in food abundance of the past 60 years had an effect on his health? This thought triggered a sudden burst of anxiety.
However, while staring into my newborn son’s eyes that could barely open in the crude light of the maternity ward, I reassured myself. Thanks to the progress of science, my son will belong to the first generation of people who will be fully aware of the power they hold on the biological fate of their children. Compared with his predecessors, he will live more free to govern, if not his own destiny, then at least the destiny of his offspring.