The mysterious disappearance of the Neanderthals could have been linked to preeclampsia, a complication that endangers the life of the fetus and/or the mother even in the postpartum period, believes a team of doctors involved in a new study, but some experts in paleoanthropology are not convinced, reports Live Science on Thursday, citing a study published on January 30 in the Journal of Reproductive Immunology.
Preeclampsia and eclampsia – a related disorder involving one or more tonic-clonic seizures or coma during pregnancy or the postpartum period – “were never seriously considered in hypotheses regarding Neanderthal reproductive biology and their eventual extinction“, claims an international team of neonatologists and gynecologists, according to the prestigious publication, reports Agerpres.
Although not fully understood by medical experts, these conditions appear to be linked to an evolutionary peculiarity of the human placenta – which, given the number of genes we share with Neanderthal man, could have affected the Neanderthal placenta as well.
What does preeclampsia mean?
Preeclampsia involves dangerously high blood pressure and can put pressure on the heart and other organs of the pregnant woman, including the kidneys and liver. The condition is found in up to 8% of current pregnancies and can also occur in the postpartum period. It can also progress to eclampsia, which involves convulsions and, sometimes, brain damage. If left untreated, both conditions can be life-threatening for both the pregnant woman and the fetus.
Research on preeclampsia has shown that the abnormal and superficial implantation of the placenta in the uterus can be a possible cause of the condition.
The exceptional metabolic demands of large-brained human babies were likely responsible for the deep implantation of the placenta to ensure sufficient maternal-fetal nutrient transfer, the researchers wrote.
An improperly placed placenta will struggle to get adequate nutrients to the fetus, which can lead to an increase in maternal blood pressure, especially in the third trimester, when the fetus’s brain is developing rapidly, according to this hypothesis. This can lead to preeclampsia, eclampsia and fetal growth restriction, all of which complicate pregnancy and threaten the survival of mothers and babies.
“They could be missing a key protective mechanism”
Given this perspective on preeclampsia, the authors of the study concluded that this condition “could have constituted an additional, underappreciated selective pressure on Neanderthals, contributing to their extinction”.
They hypothesized that Neanderthals “they may have been missing a key protective mechanism” against preeclampsia, which some of the study authors had previously suggested was present in modern humans. This idea, however, is still speculative and such a mechanism has not yet been discovered.
If Neanderthals lacked a “maternal safety mechanism” to avoid preeclampsia, this could have led to reproductive losses and maternal mortality, thus hastening their extinction as a group, the team proposed.
But experts in Neanderthal archeology and genetics are not convinced, especially since the new study provides no evidence that Neanderthals experienced preeclampsia.
“The hypothesis that Neanderthals went extinct due to preeclampsia far exceeds the available evidence,” Patrick Eppenberger, head of the Evolutionary Pathophysiology and Mummy Studies Group at the Institute for Evolutionary Medicine in Zurich, who was not involved in the study, told Live Science in an email.
Although she agreed that preeclampsia is uniquely human and related to the evolution of the human placenta, Eppenberger said that “what is much harder to support is the claim that it was more common or more lethal in Neanderthals than in early Homo sapiens, or that it played a major role in their extinction, especially given the long persistence of Neanderthals” over more than 300,000 years.
“Why Neanderthals disappeared is a question that has captured the imagination of the public and researchers, and everyone is looking for indisputable proof.” April Nowell, a paleolithic archeology specialist at the University of Victoria in Canada, told Live Science.
“I’m not particularly convinced by this study”
The reasons for the disappearance of the Neanderthals are complicated.
“I have long argued that the differential survival of the smallest Neanderthals is essential to understanding the Neanderthal story, but I am not particularly convinced by this studyNowell said.
If the researchers are correct that H. sapiens developed a mechanism to mitigate preeclampsia, Nowell said, the condition may have contributed to the extinction of Neanderthals. But given the widespread evidence of gene sharing between groups of people, “in my opinion, it is equally possible that Neanderthals, Denisovans and Homo sapiens shared this attenuation mechanism”Nowell said.
