Researchers at Karolinska Institutet, working with an international team including Max Planck Institute scientists, found that a growth hormone receptor variant inherited from Neanderthals roughly 47,000 years ago makes cells respond more strongly to growth hormone, resulting in greater muscle mass in adult carriers.
In lab tests, cells carrying the Neanderthal variant grew 40% more than cells with the common modern human receptor when exposed to growth hormone. Analyzing data from more than 1.1 million adults, the team found carriers averaged about 270-285 grams more muscle mass than non-carriers, though the effect was absent in over 6,000 children aged 11 and younger, suggesting it kicks in only after puberty.
The variant is rare in Europeans (about 0.5%) but far more common in South and East Asian populations, reaching up to 24% in some groups. Carriers also showed subtle jaw and tooth-root differences reminiscent of Neanderthal anatomy. Lead researcher Hugo Zeberg cautioned the gene is just one of many factors shaping body composition. The study was published in Current Biology on August 5, 2026.