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 .

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 .