A gene variant inherited from Neanderthals may help some modern humans build more muscle, according to a new study. The genetic change entered the human gene pool tens of thousands of years ago, when Neanderthals and modern humans interbred.
Researchers identified the variant in the growth hormone receptor gene, which influences how cells respond to growth hormone. Compared with the receptor found in most modern humans, the Neanderthal version contains two amino acid changes and one deletion. Scientists estimate that modern humans acquired the variant through interbreeding approximately 47,000 years ago.
“The most noticeable characteristic would likely be greater muscle mass, around 270 grams [9.5 ounces] per copy of the variant,” study co-author Hugo Zeberg, a geneticist at the Karolinska Institute in Sweden, told Live Science in an email. “A person who inherited two copies, one from each parent, could therefore have more than half a kilogram [1.2 pounds] of additional muscle mass.”
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The study, published Aug. 5 in the journal Cell, found that nearly all Neanderthals carried the gene variant. It is much less common among modern humans, appearing in roughly 10% of people overall. The variant was found in about 1% of people with European ancestry and as many as 25% of people with Southern Asian or Southeast Asian ancestry. Researchers did not detect it in people of African ancestry, possibly because Neanderthal-modern human interbreeding occurred in Eurasia.
How the Neanderthal gene variant affects cells
The human body naturally produces growth hormone in the brain’s pituitary gland. This hormone promotes growth during childhood and adolescence and continues to influence metabolism and other functions throughout adulthood. Some people produce too much or too little growth hormone, although these conditions can often be treated medically. The pituitary gland also produces hormones involved in metabolism, ovulation and testosterone production.
To investigate the variant, researchers analyzed 10 Neanderthal DNA samples and two Denisovan DNA samples recovered from archaeological sites across Europe, the Balkans, Siberia and Asia. Denisovans were a close evolutionary relative of Neanderthals.
The team then compared the ancient DNA findings with data from modern biobanks containing more than 1.1 million human genomes, along with information about participants’ physical characteristics.
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In laboratory experiments, the researchers modified cells so they expressed either the typical modern human version of the growth hormone receptor gene or the Neanderthal variant. When exposed to growth hormone, cells carrying the Neanderthal version multiplied about 40% more often.
However, inheriting the Neanderthal gene variant does not necessarily mean a person will look noticeably bulkier. The effects appear to be more subtle. For example, people with the variant may produce higher levels of a signaling protein after exposure to growth hormone, according to the researchers.
The variant was also associated with slightly shorter tooth roots and small differences in jaw shape. These traits resemble features identified in Neanderthals, who went extinct around 40,000 years ago.
Neanderthals disappeared around 40,000 years ago, but their DNA continues to influence some modern human traits.
(Image credit: gorodenkoff via Getty Images)
Did this gene make Neanderthals more muscular?
Neanderthals were generally stockier and more robust than modern humans. But Zeberg said the growth hormone receptor variant cannot fully explain the characteristic Neanderthal body shape.
“It cannot explain the Neanderthal body type on its own,” he said. “Neanderthal robustness was almost certainly shaped by many genes, as well as by development, lifestyle, and environmental factors. Our results provide one possible piece of a much larger puzzle.”
The placenta produces a form of growth hormone for developing fetuses that differs from the hormone released by the pituitary gland. The Neanderthal receptor variant does not appear to respond to placental growth hormone. This may explain why Neanderthal babies were similar in size to modern human babies at birth but grew more quickly afterward, Zeberg said.
The researchers found that children aged 11 and younger who carried the variant did not show the same effects. The differences appeared mainly in older individuals, suggesting that the gene’s influence may emerge around puberty, when pituitary growth hormone levels increase.
“Growth hormone is also particularly important during puberty, when its levels rise substantially,” Zeberg said. “The effect of the variant is therefore likely to be especially important during puberty and later development, rather than before birth.”
Kornelius Kupczik, a paleoanthropologist at the University of Chile in Santiago who was not involved in the research, said the high frequency of the Neanderthal gene variant among people with South and Southeast Asian ancestry was particularly noteworthy because it is relatively rare among Europeans.
The finding suggests that ancient human migrations and interbreeding may have been more complex than previously thought. Kupczik said the ancestry pattern raises important questions that require further research.
How much do you know about our closest human relatives? Test your knowledge with our Neanderthal quiz!
