Why are some women more prone to miscarriages and fertility problems, and others are not?
Our long-dead human cousins the Neanderthals are playing a part in helping a significant number of women have more babies and less problems during pregnancy.
This finding came from analysis of UK Biobank data.
It showed that almost one in three women in Europe have inherited a gene variant from Neanderthals that is associated with increased fertility, fewer bleedings during early pregnancy and fewer miscarriages.
The gene variant results in higher levels of the receptor for progesterone, a hormone important for preparing the uterine lining for egg implantation and for maintaining the early stages of pregnancy.
“The progesterone receptor is an example of how favourable genetic variants that were introduced into modern humans by mixing with Neanderthals can have effects in people living today,” said one of the study’s co-authors, Dr Hugo Zeberg, an assistant professor and researcher at the Department of Neuroscience at Karolinska Institute and the Max Planck Institute for Evolutionary Anthropology.
“The proportion of women who inherited this gene is about 10 times greater than for most Neanderthal gene variants. These findings suggest the Neanderthal variant of the receptor has a favourable effect on fertility.”
Molecular analyses revealed that “these women produce more progesterone receptors in their cells, which may lead to increased sensitivity to progesterone and protection against early miscarriages and bleeding.”
If the progesterone level is low during early pregnancy, it means the embryo is not doing well.
Neanderthal genes are a gift that keep on giving
Most Europeans and Asians have about two per cent Neanderthal DNA in their genome, and some have closer to 3 per cent.
This is a legacy of when Homo Sapiens and Neanderthals met and mated about 50,000 years ago.
As this new research, and previous studies have shown, during those mysterious those long-ago fireside encounters, modern humans picked up Neanderthal genes that continue to shape our health and even our habits.
Neanderthal DNA has had a determining impact on how we sleep (night owls or early risers), how often we get sunburned, if we’ll take up smoking, if we’ll be prone to loneliness or a depressed mood, and even how tall we are.
Too much fat in your legs such they look funny? Neanderthals.
Do you like eating pork? Neanderthals.
Some of these genes have been beneficial, but others less so.
A 2014 Harvard study showed that remnants of Neanderthal DNA in modern humans were associated with genes affecting type 2 diabetes, Crohn’s disease, lupus, biliary cirrhosis and smoking behaviour.
In 2018, Stanford University scientists found that “Neanderthal genes likely gave us some protection against viruses that our ancestors encountered when they left Africa”.
Sometimes, genes that worked well in the very old days can work against us in modern life.
A gene variant linked to blood clotting would have been useful as a response to being injured on the hunt.
Today that same variant could play a part in you having a stroke.
Finally, getting back to reproduction.
A 2008 study found that Neanderthals had a brain at birth of a similar size to that of modern-day babies.
In other words, childbirth was as much of a trial for our ancient cousins, as it is today.