Many People Today Carry A Neanderthal Growth Gene Linked To More Muscle

Some people today carry a growth-regulating gene inherited from Neanderthals. New research shows the gene makes cells grow faster in lab models, is linked to more muscle mass, and shapes facial features consistent with Neanderthal anatomy.

A study published in Current Biology found that a variant of the growth hormone receptor gene, carried by some modern humans due to ancient interbreeding with Neanderthals, produces a stronger cellular growth signal than the standard human version. The physical differences that show up in carriers today, from body size to jaw shape, trace back to that one signal running hotter.

Neanderthals lived across western Asia and Europe before going extinct around 42,000 years ago, but their DNA lives on in people today. Those with non-African ancestry carry roughly 2% Neanderthal DNA on average, from ancient encounters between the two groups. This research zeroes in on one stretch of that DNA with measurable effects on the body, though nearby genes may also play a role, and it is just one piece of a larger picture.

A Neanderthal Growth Gene Left Its Mark on the Receptor

Neanderthals were not just older humans. They had a robust build, prominent brow ridges, barrel-shaped rib cages, greater muscle mass, and shorter tooth roots than modern humans. Scientists have long suspected genetics drove these differences, but pinning down which genes were responsible has been difficult.

Researchers focused on growth hormone, produced by the pituitary gland, which plays a central role in how bones, muscles, and cartilage develop. When overactive in modern humans, it causes acromegaly, marked by enlarged bones and muscle mass; when underactive, it leads to a form of dwarfism. Examining genes across three high-quality Neanderthal genomes, the team found meaningful differences in the growth hormone receptor gene.

All three Neanderthal genomes carried two changes in the receptor’s protein-coding sequence, plus a deletion with its own separate evolutionary history. These changes appeared consistently in the high-quality genomes and were absent from the sub-Saharan African genomes examined, one clue that the version found in people today came from Neanderthals through ancient interbreeding.

Cells With the Neanderthal Gene Grew 39% Faster

To find out what these changes actually do, researchers used a mouse cell line that depends on external signals to grow and does not naturally produce the growth hormone receptor. Engineering the cells to carry either version let scientists directly compare how each performed.

Cells with the Neanderthal receptor grew faster when exposed to pituitary growth hormone, ending up 39% more numerous after five days. The whole effect traced back to one tiny swap in the receptor, at a spot researchers call position 561, which revved up the cell’s internal growth signal by 22% and pushed the growth rate itself up by 6%.

One finding stood out: exposed to placental growth hormone, made during pregnancy, the two receptors showed no difference at all. Whatever makes the Neanderthal version more responsive only kicks in after birth. The authors think this might trace back to the physical demands of childbirth itself, though they’re careful to call that an educated guess rather than a proven mechanism. That pattern holds up elsewhere too: carriers show no differences in birth weight or childhood measurements up to age 11, but the gap shows up clearly once they reach adulthood.

Carriers Today Have More Muscle and Neanderthal-Like Facial Traits

Using data from more than 1.1 million adults across five genetic databases, plus a birth study and MRI scans, researchers built a detailed picture of what carrying this variant means for the body.

Adults with the variant average 0.30 centimeters taller and 285 grams heavier per copy. Most of that extra weight looks like muscle rather than fat: carriers showed about 150 grams more muscle in the arms and legs, plus more lean tissue packed into the torso. Hips were a bit bigger too, and carriers actually ran leaner overall, pointing to muscle and bone rather than added fat.

Facial differences were also detectable. Carriers tend to have a shorter distance between the jaw joint and jaw corner, averaging 3.6 millimeters shorter per copy across four studies, and were more likely to have an overbite, with roughly 2.8 times the odds of non-carriers. Some studies found shorter tooth roots in carriers too, a trait noted in early examinations of Neanderthal remains.

The Neanderthal Gene Spread Widely, and Its Effects Are Real but Modest

This variant is rare in Europe, at just 0.5%, but climbs fast heading east: 15% in East Asia, 20% in South Asia, and as high as 24% in Pakistan. Tracking it through nearly 10,000 ancient genomes going back 10,000 years shows those numbers have barely budged, suggesting nothing has been actively pushing the gene up or down over that stretch.

A single amino acid swap, carried from a species extinct for tens of thousands of years, is statistically linked to differences in muscle, height, weight, and face shape in millions of people today. The lab work backs up the connection, though it doesn’t prove the gene causes every trait on its own. Either way, it’s a small, concrete reminder that the distant past still shapes bodies now.

---