What is the Neanderthal gene variant linked to greater muscle mass in modern humans, what specific genetic changes define it, how did it enhance growth hormone response in lab tests, how much additional muscle mass do carriers average, which populations carry it at the highest fr

How It Enhanced Growth Hormone Response in Lab Tests

When researchers inserted the Neanderthal GHR into lab-grown cells (both human and mouse cell lines) and exposed them to growth hormone:

• Cells with the Neanderthal receptor proliferated significantly faster than cells carrying the modern human version .
• They grew up to 40% more than cells with the common modern receptor over the course of the experiment .
• Specifically, mouse cells with the Neanderthal receptor grew 39% more by day 5 .
• The P561T substitution alone accounted for the majority of this effect: 6% faster cell growth and 22% more activated signaling protein downstream .

The Neanderthal receptor produces a stronger intracellular signaling response when bound by growth hormone, making cells more sensitive to growth signals .

Additional Muscle Mass in Carriers

In a large-scale analysis of over 1.1 million adults, carriers of the Neanderthal GHR variant averaged:

• ~250–285 grams (~0.55–0.63 lbs) more lean muscle mass
• ~0.3 cm (~0.12 inches) greater height

The effects on muscle mass appear to emerge only after childhood .

Populations with the Highest Frequencies

The variant is absent in people from sub-Saharan Africa, since Neanderthal admixture occurred after the Out-of-Africa migration . Among non-African populations, carrier frequencies are:

• ~20% in South Asian populations
• ~15% in East Asian populations
• ~1–4% in European populations
• The variant is also present in Indigenous American populations (exact frequency not separately specified in available sources but noted as common in the Americas alongside East/South Asian groups)

About 94% of sequenced Neanderthal genomes carried the variant, compared to fewer than 10% of modern humans globally .

When Interbreeding Introduced It

The Neanderthal GHR variant entered modern human gene pools through interbreeding between Neanderthals and the ancestors of non-African modern humans, estimated at around 47,000 years ago .

Associated Skeletal Traits

Beyond muscle mass, the Neanderthal GHR variant is linked to subtle changes in skeletal morphology, including:

• Jaw shape differences
• Tooth morphology changes

These traits align with the more robust facial structure characteristic of Neanderthals .

Lead Researchers' Caution

The lead researchers emphasized that the effect, while statistically significant, is modest at the population level — roughly a quarter-kilogram of extra muscle and a few millimeters of extra height . They cautioned that the variant is not a "super-muscle gene" that produces dramatic physique differences. Instead, it represents a small, accumulated effect from ancient introgression that only becomes detectable in large-scale cohort studies . The study's authors also noted that the variant's functional significance should not be overstated, as many other genetic and environmental factors contribute far more to individual variation in muscle mass .