Neanderthal gene variant boosts lean muscle mass in modern humans

An international team of scientists has identified a possible genetic reason why Neanderthals were considerably stockier and more muscular than modern humans, ERR reported. A gene variant inherited by modern humans through interbreeding thousands of years ago still increases lean muscle mass in many people today.

The Neanderthal lineage split from the ancestors of modern humans about half a million years ago and established itself in Eurasia. In harsher conditions, Neanderthals had a more robust build, thicker bones and broader shoulders.

Although scientists have studied ancient DNA sequences for more than 15 years, some of the genetic material responsible for the Neanderthals’ powerful physique had remained unidentified. A study published in the journal Current Biology found that one factor may lie in the growth hormone receptor.

Hugo Zeberg, an evolutionary anthropologist at the Karolinska Institute, noticed a small change in a gene that controls the growth hormone signalling pathway. The finding immediately appeared to biologists to be a promising lead.

The pituitary gland releases substances into the bloodstream that travel throughout the body. Special receptors on the surface of muscle and bone cells receive these signals. Molecular analysis showed that the gene responsible for the Neanderthal receptor lacks the third exon, one of the sections of genetic material used by the body to produce essential building blocks.

Two amino acids had also been replaced. One of these changes makes the receptor on the cell surface exceptionally sensitive to hormones, giving the cell a stronger signal to divide and grow.

To test the suspected biochemical effect, the researchers introduced both modern human and Neanderthal gene variants into cells. When exposed to a pituitary hormone, cells with the Neanderthal-type receptor multiplied almost 40 percent faster. The intracellular signalling pathway operated significantly more actively with the ancient genetic code.

The system also has an important safeguard. During pregnancy, a woman’s body produces placental growth hormone. The Neanderthal receptor responded to this hormone normally, preventing the birth of dangerously large babies. Health data confirmed that babies carrying the Neanderthal gene variant did not weigh more at birth than other babies.

The growth boost appears to switch on later in life. Children carrying the variant do not differ from their peers in height or weight until the age of 11. Rapid growth probably begins during puberty, when levels of hormones released by the pituitary gland increase severalfold.

The genetic variant reached modern humans through interbreeding in the distant past. The ancestors of modern humans and Neanderthals produced offspring together about 47,000 years ago. Today, fewer than 10 percent of people worldwide carry the variant.