Men’s childhood traumas may damage their sperm and they may pass on the effects to their children, a new study suggests.
For centuries, the idea that animals or humans could inherit traits that their parents had developed over the courses of their lives has been dismissed in favor of the widely-accepted idea that we only inherit genetic traits.
But recent research has complicated that line. The number of studies showing how environment and lifestyle can impact sperm and eggs, altering what gets passed on.
In addition to evidence of the effects of obesity and pollution on sperm, new research from Tufts University found changes to the sperm of men who had experienced childhood trauma – and the traits could be passed on.
Men who went through childhood traumas may pass along their stress through their sperm, which may itself be damaged by stress
Before Charles Darwin cornered the market on evolutionary theory, Jean-Baptise Lamarck put forth a very different concept of what we get from our parents and how.
Two centuries ago, Lamarck proposed that animals changed over their lives and then passed their acquired traits onto their children.
His pet example to support is theory was the giraffe, which, Lamarck claimed, got its long neck by stretching it to reach leaves, then passed the trait to its children.
The theory has since been debunked, dismissed and even ridiculed by science.
Until the dawn of epigenetics.
Epigenetics is the study of changes to the ways that genes are expressed, or appear, rather than looking solely at what the genetic code says.
First scientists started to see how roundworms could pass changes to their biology – namely, a developed immunity to a virus – to their offspring.
Since then the field of epigenetics has exploded, revealing more and more ways that an organism’s environment and experiences can alter the expressions of its genes and hand them down to their offspring.
Much of this research has focused on how environmental factors can alter the reproductive cells.
In previous research, scientists have found that a component of genetics, miRNAs, are impaired in mice who are exposed to traumatic stressors early in their lives.
RNA is a part of genetic material, carrying the messages that are encoded to DNA to the proper places to manufacture proteins.
Until quite recently, scientists thought that male sperm contributed only DNA, not RNA to an embryo.
But now we know that some RNA is in fact transferred from male sex cells.
Correspondingly, doctors and scientists have also come to recognize more and more ways that a father’s health – not just the mother’s – affects the development of his children.
The miRNAs that a sperm contribute to an egg in fertilization regulate sets of genes in the offspring and how these genes are expressed.
Researchers have found that human miRNA are affected by a number of environmental and lifestyle factors including obesity and smoking, and the overall quality of men’s sperm is known to be diminished by stress.
Now, the new study’s findings suggest that childhood traumas and their effects on men for the rest of their lives may also be passed to their children.
The Tufts University authors compared two findings: the changes they noted in the sperm of mice that had experienced early life traumas and the sperm of men that reported early life traumas.
The two data sets had compelling overlaps, with the scientists observing remarkably similar – and strikingly extreme – changes in the sperm of both the mice and men.
A small sample of 28 white men filled out surveys asking them to rate levels of emotional, physical, verbal and sexual abuse from there childhoods, as well as experiences of physical and emotional neglect.
Surprisingly, about 10 percent had had enough bad experiences to qualify for being at risk of later mental and physical health issues.
These likely victims of trauma also showed the same changes to their sperm miRNA as the mice who had experienced trauma as pups.
Men who scored highest on the abuse questionnaire – indicating the most trauma – had 300 times less of the two sperm miRNAs that play vital roles in embryo development, particularly the formation of their brains and own sperm (for males).
The mice pups born of stressed fathers showed the same sperm changes, as well as behavioral indicators of trauma.
‘This is the first study to show that stress is associated with altered levels of sperm miRNAs in humans,’ said lead study author Dr David Dickson.
‘We are currently setting up a new, larger study in men, and additional experiments in mice that could yield further support for the idea that changes in these sperm miRNAs do, in fact, contribute to an elevation of stress-related disorders across generations.’