Tens of thousands of years after Neanderthals disappeared as a distinct human population, part of their biology continues to live on in modern humans. A new genetic study suggests that a version of the growth hormone receptor inherited from Neanderthals can influence muscle mass, height and several subtle characteristics of the human skeleton.
Neanderthals had a more robust physique than most modern humans. Their skeletal remains reveal powerful bodies, distinctive skull structures and several other anatomical characteristics.
Scientists have long tried to determine how much of these differences resulted from lifestyle and how much was genetically determined.
The new research focuses on the growth hormone receptor known as GHR. This protein is found on the surface of cells and responds to growth hormone, helping regulate the development of bones, muscles and other tissues.
Researchers found that the Neanderthal version of this receptor contains two amino-acid changes compared with the version most commonly found in modern Homo sapiens.
Laboratory experiments revealed that one of these changes produces a substantially stronger cellular response to growth hormone. Cells carrying the Neanderthal receptor showed around 40% greater growth under specific experimental conditions.
The researchers then investigated whether the same effect could still be detected in people living today.
They analysed genetic and medical information from more than 1.13 million people across five major biobanks, together with data from 6,602 children participating in a separate British study.
The results showed that adult carriers of the Neanderthal-derived variant had approximately 270 to 285 grams more lean body mass on average. Most of the difference was associated with additional muscle tissue in the arms, legs and torso.
Carriers were also around three millimetres taller on average and had hip circumferences approximately 2.7 millimetres larger.
Researchers also identified subtle differences in jaw structure and tooth roots that resemble some anatomical characteristics associated with Neanderthals.
The effects, however, are relatively small. Carrying the variant does not automatically make someone exceptionally muscular and certainly does not determine a person’s overall appearance.
The geographical distribution of the variant is particularly interesting.
The Neanderthal-derived version of GHR is found in approximately 0.5% of Europeans. Its frequency rises to around 2% in some North and South American populations, approximately 15% in East Asia and about 20% in South Asia.
The discovery provides another example of the biological legacy created by interbreeding between Homo sapiens and Neanderthals.
Genetic evidence shows that ancestors of modern humans interbred with Neanderthals after populations of Homo sapiens migrated out of Africa. As a result, many people with predominantly non-African ancestry carry approximately 1–2% Neanderthal DNA.
These ancient genetic fragments are not simply historical relics.
Previous studies have shown that Neanderthal-derived variants can influence aspects of the immune system, skin biology, metabolism and susceptibility to certain diseases.
The new research adds another possibility: some of the physical characteristics associated with Neanderthals may still be subtly expressed in millions of people alive today.
That does not mean possessing the Neanderthal GHR variant can replace physical exercise. The researchers stress that the difference in muscle mass is modest, while training, nutrition, age and many other genes have far greater effects on physical development.
The wider significance of the discovery lies elsewhere.
It demonstrates that the disappearance of Neanderthals around 40,000 years ago did not mean the complete disappearance of their biology.
Part of their genetic legacy survives within Homo sapiens, and tens of thousands of years later it can still influence how some human bodies grow and develop.
Sources: Current Biology, Max Planck Institute for Evolutionary Anthropology, Karolinska Institutet.
