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Humans still evolving

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• Study finds natural selection favours larger ‘hunky’ men with high BMI, younger mothers
• Natural selection ‘weeding out’ diseases in humans

Humans are not quite done evolving, a dramatic new study has found.

Researchers analyzing genetic and health data on hundreds of thousands of people, uncovered evidence to suggest natural selection has an ongoing, albeit small, effect on modern humans.

The new study appears to be favour larger, ‘hunkier’ men with a greater body mass index, and younger mothers.

In the new study, researchers analyzed data from the UK Biobank, looking at a number of factors among people aged 45 and older.

While the effects may be weak, the researchers say it does appear natural selection continues to be shaping human evolution.

In men, the research found that having a high BMI appears to be favoured.

This is likely linked to higher muscle bulk rather than obesity, given the fertility problems associated with the latter, the Guardian reports.

And, the study found that natural selection appears to favour women who get a young start on having a family.

The researchers say this shows natural selection, while weak, is ‘observable’ in humans – though modern medicine and other factors may have a bigger influence.

Researchers examined data from the UK Biobank, looking at genetic variants and their correlation to the number of children people had during their lifetime.

Of the people included in the study, all were aged 45 and older.

The team analyzed several traits, including height, body mass index, and age at first birth (for women), to reveal how evolutionary processes may be at play in today’s society.

“Combining high-throughput molecular genetic data with extensive phenotyping enables the direct study of natural selection in humans,” the authors explain in the new paper, published to the Proceedings of the National Academy of Sciences.

“We see firsthand how and at what rates contemporary human populations are evolving.”

While the effects may be weak, the researchers say it does appear natural selection continues to be shaping human evolution.

From height to waist circumference, the study found natural selection tends to disfavour extremes.

“Here we demonstrate that the genetic variants associated with several traits, including age at first birth in females and body-mass index in males, are also associated with reproductive success,” they wrote.

For babies, however, this may not necessarily be the case.

While previous studies have shown that extreme weights are not favoured in babies, the study found this effect is now very weak, and only existed among females.

The shift, experts say, may boil down to modern advancements in neonatal care, which allow both underweight and overweight babies to eventually thrive, according to the Guardian.

In men, the research found that having a high BMI appears to be favoured. This is likely linked to higher muscle bulk rather than obesity, given the fertility problems associated with the latter.

NATURAL SELECTION IS ‘WEEDING OUT’ DISEASES IN HUMANS
A massive study analyzing the genomes of 210,000 people in the United States and Britain has found a range of diseases including are being ‘weeded out’ of the human gene pool by natural selection.

Researchers found the genetic variants linked to Alzheimer’s disease and heavy smoking are less frequent in people with longer lifespans, suggesting that natural selection is weeding out these unfavorable variants in both populations.

New favorable traits evolve when genetic mutations arise that offer a survival edge. Though it may take millions of years for complex traits to evolve, say allowing humans to walk on two legs, evolution itself happens with each generation as adaptive mutations become more frequent in the population.

Researchers also found sets of genetic mutations that predispose people to heart disease, high cholesterol, obesity, and asthma, also appear less often in people who lived longer and whose genes are therefore more likely to be passed down and spread through the population.

In women over 70, researchers saw a drop in the frequency of the ApoE4 gene linked to Alzheimer’s, consistent with earlier research showing that women with one or two copies of the gene tend to die well before those without it.

Researchers saw a similar drop, starting in middle age, in the frequency of a mutation in the CHRNA3 gene associated with heavy smoking in men.

And, the study found that natural selection appears to favour women who get a young start on having a family.

“Natural selection is still happening in modern humans – it is observable, we can detect it,” co-author Janeal Sanjak, from the University of California, Irvine, told the Guardian.

“But they are fairly weak effects and secular trends, things due to modern medicine and social change, are likely to be bigger drivers of changes in these traits.”

The study also suggested that natural selection is favouring reduced educational attainment in women.

But, it seems, that is not a straightforward link, with further analysis revealing that the result is likely linked to selection on the age of starting a family, with younger mothers less likely to have reached higher levels of education, or less able to reach them once having had children.

The study may be the first to take a direct look at how the human genome is evolving in a period as short as one or two generations.

As more people agree to have their genomes sequenced and studied, researchers hope that information about how long they lived, and the number of kids and grandkids they had, can reveal further clues about how the human species is currently evolving.

Dozens of firms already offer the service, and it is expected to get easier and cheaper in the future.


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