Neanderthals disappeared about 40,000 years ago, but their DNA may now be helping some modern humans build more muscle

A gene inherited from Neanderthals may be helping some modern humans carry more muscle, offering scientists a new clue to the muscular and robust build of our ancient relatives.

Neanderthals and modern humans diverged from a common ancestor about 500,000 years ago. While the ancestors of modern humans continued evolving in Africa, Neanderthals followed a separate evolutionary path across Europe and Asia before disappearing roughly 40,000 years ago.

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Their skeletons show just how different their bodies were. Neanderthals had thick, dense bones, large areas where muscles attached to the skeleton, and broad chests and shoulders. Scientists have studied Neanderthal DNA for more than 15 years, but identifying the genes behind their muscular build has been difficult.

Now, researchers have identified a genetic variant inherited from Neanderthals that appears to influence the growth hormone pathway and increase muscle mass in people who carry it today.

The discovery came when evolutionary anthropologist Hugo Zeberg of the Karolinska Institute examined genetic differences between modern humans and Neanderthals. One variant stood out because it affected the growth hormone receptor gene, which plays a key role in telling cells to grow.

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Growth hormone is released into the bloodstream by the pituitary gland and binds to receptors on cells, including muscle and bone cells. The Neanderthal version of the receptor appears to be more responsive to the hormone, producing a stronger signal for cells to grow and multiply.

The genetic variant is believed to have entered modern human populations through interbreeding with Neanderthals about 47,000 years ago.

It is also much more common in some populations than others. The variant is found in roughly 15% of East Asian genomes and 20% of South Asian genomes, compared with about 0.5% among people of European ancestry and 2% among Indigenous Americans, according to the researchers.

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Laboratory experiments provided another striking clue. Researchers created cells carrying either the Neanderthal or modern human version of the gene and exposed them to growth hormone. Cells carrying the Neanderthal version grew about 40% larger than cells carrying the more common modern human version.

The researchers then looked at biometric data from people included in large genetic databases. The pattern was similar.

People carrying the Neanderthal variant weighed an average of about 285 grams, or 0.6 pounds, more than people without it.

But the extra weight did not appear to be simply additional body fat. When researchers examined where the difference came from, they found that it was associated with an increase in lean muscle mass.

That suggests the ancient genetic variant may still be influencing body composition thousands of years after Neanderthals and modern humans interbred.

Geneticist Hannah Long of the University of Edinburgh described the findings as a compelling case that the Neanderthal version of the growth hormone receptor gene increases muscle mass in modern humans.

The researchers also found subtle physical differences among people carrying the variant. Some facial characteristics were slightly closer to those associated with Neanderthals, including shorter tooth roots and a shorter mandibular ramus, the vertical section of the jaw extending downward from the area near the ear.

But the discovery does not mean scientists have found a single gene responsible for the entire Neanderthal physique.

Zeberg cautioned that the identified variant cannot explain all Neanderthal physical characteristics. Other genes, along with environmental factors, would also have influenced their musculature, facial structure and overall body shape.

The finding nevertheless offers a rare glimpse into how ancient DNA continues to influence people today. A genetic change that entered modern human populations through contact with Neanderthals nearly 47,000 years ago may still be helping some people develop slightly more lean muscle mass.

In other words, part of the robust Neanderthal build may have survived—not in fossils or museums, but in the DNA of people living today.