If you happen to carry a certain piece of Neanderthal DNA, you likely have more muscle than people who do not, and now, scientists know why.
A new study has identified a Neanderthal version of a gene that makes the body respond more strongly to growth hormone, resulting in considerably more muscle mass in adults who carry it. The variant, inherited through interbreeding between modern humans and Neandertals roughly 47,000 years ago, is still carried by millions of people today.
“What struck me most was that two very different types of evidence told the same story,” Philipp Kanis, first author of the study and a postdoctoral researcher at Germany’s Max Planck Institute for Evolutionary Anthropology, said in a statement. “Cells grown in the laboratory responded more strongly, while data from more than a million people showed signs of the same effect in the body.
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“It is rare to see laboratory and population evidence fit together so clearly.”
Neanderthal Variant Responds More Strongly To Growth Hormone
Growth hormone helps shape the body by controlling how muscles and bones develop. It is released by the pituitary gland at the base of the brain and travels through the bloodstream until it binds to a receptor on the surface of cells, which then relays the signal inward.
The research team, led by Hugo Zeberg of Sweden’s Karolinska Institutet and Kanis, found that the Neanderthal version of this receptor carries two amino acid changes not found in the receptor most common in modern humans today.
To test what these changes do, the researchers grew cells in the lab carrying each version of the receptor and exposed them to growth hormone. Cells with the Neanderthal receptor grew 40 percent more than cells with the modern human version. Most of that stronger response was traced to one of the two Neanderthal-specific changes.
Increased Weight and Muscle Mass in Carriers
Using body-measurement data from more than a million people, the researchers found that adults carrying the Neanderthal receptor had, on average, about 270 grams more muscle mass than non-carriers.
The effect appears to kick in later in life. Looking at more than 6,000 children, the researchers found no link between the Neanderthal variant and growth up to age 11, suggesting the effect emerges around puberty, when growth hormone levels rise sharply.
The variant was also tied to subtle skeletal differences. Carriers tended to have a slightly shorter rear section of the lower jaw and shorter tooth roots—both features closer to what is typical of ancient Neanderthals, who were generally more heavily built than most people today, with larger muscles and prominent brow ridges.
Zeberg told Newsweek: “Our results suggest that this Neanderthal growth hormone receptor variant increases signaling in cells and is associated with around 270 grams of additional muscle mass per gene copy. Someone who inherited a copy from both parents could therefore have roughly half a kilogram more muscle, although the variant is certainly no substitute for training!”
Even so, carrying the gene is no shortcut to a gym-ready physique, according to co-author Miriam Berreiter.
“As someone who does CrossFit, I was delighted to find Neandertal genetics and muscle mass coming together in the same study,” Berreiter said in a statement. “But even a Neandertal growth hormone receptor is no substitute for training.”
Newsweek reached out to the study authors for more information via email.
Reference
Zeberg, H., Berreiter, M., Kanis, P., et al. (2026). Increased signaling of the Neanderthal growth hormone receptor. Current Biology. https://doi.org/10.1016/j.cub.2026.07.025.
Contact Newsweek editors on this story: Kara Dolman and Gray R. Thomas