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2 reasons why mothers far outnumbered fathers in human history

Surprising studies revealed why mothers affected the genetic pool more than fathers.

Credit: Pixabay
  • Studies showed that in human history, mothers often outnumbered fathers.
  • This happened because of polygyny and migration patterns.
  • Modern ratio of mothers to fathers is closer to 1 to 1.

In the course of human history, have there been more mothers or fathers? By the basic logic of it, there should be as many of one as the other. But there's nothing basic about about how humans procreate, pulling their kind forward through the eons by hook or crook. It turns out, there have been significantly more mothers than fathers. A profound fact to ponder as Mother's Day comes around. Women have made a much larger genetic contribution to the world's population than men.

Certainly now the ratio is much more equal but over time it was often not so. A fascinating DNA study in 2014 found that polygyny, the practice of one man having many wives, was partially responsible for why moms outnumber dads if you look at the human population growth as a whole. Another big reason - migration patterns which often had wives leaving their towns to move in with their husbands, making females travel more. This practice would, in turn, widely spread female mitochondrial DNA, while lowering genetic variation among populations.

Study researcher Mark Stoneking, a professor of biological anthropology at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, attributed historical practices of human societies the responsibility for the phenomenon.

"Imagine a population of 100 females and 100 males," said Stoneking to the Guardian. "If all the females but only one of the males reproduced, then while the males and females contribute 50:50 to the next generation, the male contribution is all from just one male."

His team's genetic analysis looked to compare the paternally-inherited Y chromosome with maternally inherited mitochondrial DNA in samples from 623 males from 51 different populations around the world. This allowed the researchers to paint an interesting picture of human genetic migrations.

The patterns weren't the same geographically – there were stronger genetic differences for paternal than for maternal DNA in people from East Asia and Europe, pointing to higher levels of female migration. In populations from the Americas, Oceania and Africa, larger differences for maternal DNA than for paternal were found, suggesting that fewer males reproduced.

You can check out their study in Investigative Genetics.

In another proof of the effects of polygyny on human genetics, a 2015 study found that about 8,000 years ago, 17 women were reproducing for every one man. How could that happen? "It wasn't like there was a mass death of males," explained Melissa Wilson Sayres, a computational biologist at Arizona State University who was involved in that study.

According to Dr. Toomas Kivisild, a biological anthropologist on the team, the reason for the discrepancy lies in periods of human history when few men were able to accumulate so much wealth and power that they would essentially be able to prevent other less successful men from reproducing. And this wealth and power would be passed on to the sons of these men, ensuring the continual survival of their genetic lineage.

Why ‘mom guilt’ is an unreasonable term

Hints of the 4th dimension have been detected by physicists

What would it be like to experience the 4th dimension?

Two different experiments show hints of a 4th spatial dimension. Credit: Zilberberg Group / ETH Zürich
Technology & Innovation

Physicists have understood at least theoretically, that there may be higher dimensions, besides our normal three. The first clue came in 1905 when Einstein developed his theory of special relativity. Of course, by dimensions we’re talking about length, width, and height. Generally speaking, when we talk about a fourth dimension, it’s considered space-time. But here, physicists mean a spatial dimension beyond the normal three, not a parallel universe, as such dimensions are mistaken for in popular sci-fi shows.

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A new hydrogel might be strong enough for knee replacements

Duke University researchers might have solved a half-century old problem.

Lee Jae-Sung of Korea Republic lies on the pitch holding his knee during the 2018 FIFA World Cup Russia group F match between Korea Republic and Germany at Kazan Arena on June 27, 2018 in Kazan, Russia.

Photo by Alexander Hassenstein/Getty Images
Technology & Innovation
  • Duke University researchers created a hydrogel that appears to be as strong and flexible as human cartilage.
  • The blend of three polymers provides enough flexibility and durability to mimic the knee.
  • The next step is to test this hydrogel in sheep; human use can take at least three years.
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Predicting PTSD symptoms becomes possible with a new test

An algorithm may allow doctors to assess PTSD candidates for early intervention after traumatic ER visits.

Image source: camillo jimenez/Unsplash
Technology & Innovation
  • 10-15% of people visiting emergency rooms eventually develop symptoms of long-lasting PTSD.
  • Early treatment is available but there's been no way to tell who needs it.
  • Using clinical data already being collected, machine learning can identify who's at risk.

The psychological scars a traumatic experience can leave behind may have a more profound effect on a person than the original traumatic experience. Long after an acute emergency is resolved, victims of post-traumatic stress disorder (PTSD) continue to suffer its consequences.

In the U.S. some 30 million patients are annually treated in emergency departments (EDs) for a range of traumatic injuries. Add to that urgent admissions to the ED with the onset of COVID-19 symptoms. Health experts predict that some 10 percent to 15 percent of these people will develop long-lasting PTSD within a year of the initial incident. While there are interventions that can help individuals avoid PTSD, there's been no reliable way to identify those most likely to need it.

That may now have changed. A multi-disciplinary team of researchers has developed a method for predicting who is most likely to develop PTSD after a traumatic emergency-room experience. Their study is published in the journal Nature Medicine.

70 data points and machine learning

nurse wrapping patient's arm

Image source: Creators Collective/Unsplash

Study lead author Katharina Schultebraucks of Columbia University's Department Vagelos College of Physicians and Surgeons says:

"For many trauma patients, the ED visit is often their sole contact with the health care system. The time immediately after a traumatic injury is a critical window for identifying people at risk for PTSD and arranging appropriate follow-up treatment. The earlier we can treat those at risk, the better the likely outcomes."

The new PTSD test uses machine learning and 70 clinical data points plus a clinical stress-level assessment to develop a PTSD score for an individual that identifies their risk of acquiring the condition.

Among the 70 data points are stress hormone levels, inflammatory signals, high blood pressure, and an anxiety-level assessment. Says Schultebraucks, "We selected measures that are routinely collected in the ED and logged in the electronic medical record, plus answers to a few short questions about the psychological stress response. The idea was to create a tool that would be universally available and would add little burden to ED personnel."

Researchers used data from adult trauma survivors in Atlanta, Georgia (377 individuals) and New York City (221 individuals) to test their system.

Of this cohort, 90 percent of those predicted to be at high risk developed long-lasting PTSD symptoms within a year of the initial traumatic event — just 5 percent of people who never developed PTSD symptoms had been erroneously identified as being at risk.

On the other side of the coin, 29 percent of individuals were 'false negatives," tagged by the algorithm as not being at risk of PTSD, but then developing symptoms.

Going forward

person leaning their head on another's shoulder

Image source: Külli Kittus/Unsplash

Schultebraucks looks forward to more testing as the researchers continue to refine their algorithm and to instill confidence in the approach among ED clinicians: "Because previous models for predicting PTSD risk have not been validated in independent samples like our model, they haven't been adopted in clinical practice." She expects that, "Testing and validation of our model in larger samples will be necessary for the algorithm to be ready-to-use in the general population."

"Currently only 7% of level-1 trauma centers routinely screen for PTSD," notes Schultebraucks. "We hope that the algorithm will provide ED clinicians with a rapid, automatic readout that they could use for discharge planning and the prevention of PTSD." She envisions the algorithm being implemented in the future as a feature of electronic medical records.

The researchers also plan to test their algorithm at predicting PTSD in people whose traumatic experiences come in the form of health events such as heart attacks and strokes, as opposed to visits to the emergency department.

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