We have been looking for the end of Neanderthals in weapons and climate for decades. A study proposes to look for it in the placenta

For decades, we have tried to explain why our species has persisted over time and Neanderthals don’t. We have blamed climate changeto competition for resources, to a supposed cognitive inferiority and even to the genetic assimilation. However, a new study suggests that the answer might not lie on the battlefield or in the weather, but in something much more intimate like the placenta.

A new idea. In this case, science proposes a hypothesis controversial, since it suggests that Neanderthals could have become extinct, in part, due to genetic susceptibility extreme to preeclampsia. a disorder which is heard a lot today and which is nothing more than a hypertensive condition in pregnancy that can be lethal for both the mother and the fetuses.

A price to pay. To understand the hypothesis, we must first understand the human “obstetric paradox”, since in our species we have an almost unique characteristic, which is deep hemochorial placentation. And it is something that may sound very bad, but it is actually necessary to feed a fetal brain as demanding as ours and that of Neanderthals.

In this case, the placenta needs to aggressively invade the arteries of the uterus maternal to obtain maximum blood flow, although the problem is that it is something that carries a great risk.

The possibilities. Faced with this invasion, the possibilities that open up are several. The first of them is that it works and that the fetus can develop its massive brain.

But in the event that this fails, a great immunological and vascular reaction is unleashed in the mother, which is what we know as preeclampsia. This presents with severe hypertension, organ damage and risk of death for both the mother and the fetus. And it is a problem that today is quite significant among human pregnancies, but now science indicates that, although the Homo sapiens evolved a physiological “safety mechanism” to mitigate this impact, Neanderthals were not so lucky.

A demographic winter. This study suggests that, as the Neanderthal brain grew, becoming larger than ours, its metabolic needs forced a increasingly aggressive placentation. The fact of penetrating further into the placenta significantly increases the risk of preeclampsia, and the problem is that Neanderthal women lacked the immune mechanism to tolerate this invasion.

This is where researchers have created a scenario in which rates of preeclampsia and eclampsia in Neanderthals could have reached between 10% and 20% of all pregnanciescompared to much lower rates in preindustrial humans.

The meaning. This scenario translates into logically devastating maternal and fetal mortality, and the direct consequence is that small and dispersed hunter-gatherer populations had a constant decline in reproductive success. And this is a much more effective death sentence than any war, since a sudden catastrophe is not necessary, but it is enough for more mothers and babies to die than are born over a few millennia for a species to end up disappearing.

There is skepticism. Within the scientific world there are doubts about what is said in this study, since there is a lack of physical evidence to support this hypothesis. The first thing they point to is that there are no markers in the fossils that have been found that allow us to diagnose preeclampsia in a Neanderthal woman from 40,000 years ago.

In addition to this, although we know genetic variants associated with the risk of preeclampsia in modern humans, such as genes linked to FLT1systematic screening of Neanderthal DNA has not yet been performed to confirm whether they possessed the “high-risk” variants or lacked the protective variants.

Also like it. What makes this hypothesis attractive to biologists is that it fits with maternal-fetal conflict theory. As different previous reviews point out, pregnancy is not always a perfect cooperation, but rather a tense biological negotiation.

In this case, the fetus “wants” more resources to survive, and the mother “wants” to limit that investment to survive and have future children. Preeclampsia is often the result of this conflict getting out of control, and so, if Neanderthals took the “big brain” strategy to the limit without developing the biological counterpart to protect the mother, their own reproductive biology could have become an evolutionary trap.

Images | Nanne Tiggelman freestocks

In Xataka | A mixture of 4,000 kilometers: we have the first detailed map of the coexistence between Neanderthals and Sapiens