Most of us have been lead to believe we are the product of two things, genetics and our environment. Now it seems things have gotten a bit more complicated.
We learned about Darwinian evolution in school. We learned that random mutations occur and when they increase the ability of the individual to survive and reproduce, they are propagated into future generations, and by this mechanism, over many generations a species adapts to it’s environment.
Now it seems evidence exists that environmental influences in our lives actually influence our children and their children. For example, if men endure a food shortage during their lives, especially between the ages of nine and twelve, then their grandsons will live longer. A father enduring a food shortage does not confer a longer life expectancy this his granddaughters.
A woman enduring a food shortage during her life will confer a longer life expectancy to her granddaughters, but rather than the age of 9-12 having the most impact, a food shortage during the fetal stage has the most effect. A woman enduring a food shortage will not confer any longer life expectancy to her grandsons.
If men smoke before age 11, their grandsons will be larger. Their daughters will not be affected. Somehow, something in the environment can affect the mens sperm in such as way that it alters only the men in future generations. Environmental influences affect womens eggs in such a way that it affects women in future generations. The mechanism is not presently understood.
It is interesting that environmental effects on men only affect male descendants and environmental effects on women only affect female descendants. Most genetic changes affect both sexes of future generations except those specifically linked to the sex chromosomes.
How environmental influences could affect germ cell genetics in such a way that the modified traits are relevant and effect only the same sex as the germ cell carrier is hard to contemplate. It is clear that there is much about genetics and particularly as applied to sexual reproduction that we do not understand.
One factor that can affect expression of various genetic instructions during ones lifetime is a process known as methylization. it is this mechanism that prevents junk DNA from being expressed. Methyl groups are attached to sites on our DNA preventing their expression but there is no known mechanism for these changes to be inherited, nor is there any reason that it would only affect individuals of the same sex.
I’m falling asleep at the keyboard, need to continue this at another time…