Shana - the daughter of a Neanderthal father and a Homo sapiens mother
Cover illustration for my book The Way of the Wolf
Cover illustration for my book The Way of the Wolf
AI-generated image (ChatGPT 5.2)
Evolutionary history is often represented as a neatly branching tree: an ancestral population divides, its descendants diverge, and each resulting lineage continues along its own independent path. Real evolution, however, is frequently much less tidy.
As I explained in my previous post on the Hawaiian honeycreepers, lineages that have begun to diverge can subsequently meet again and exchange genes through hybridisation. The result is reticulated evolution: an evolutionary history that is partly tree-like but also contains connecting branches where genes have passed between related populations.
The same principle applies to our own ancestry.
Modern humans, Neanderthals and Denisovans were not separately created, genetically sealed “kinds”. They were closely related human lineages produced by population separation and divergence, but that separation was never absolute. When populations encountered one another again, they sometimes interbred, allowing genes from one evolutionary branch to enter another—a process known as introgression.
Much of the resulting Neanderthal-derived DNA carried by people today may have little or no detectable effect. Some introgressed variants, however, continue to influence human biology. An international team led by Philipp Kanis of the Max Planck Institute for Evolutionary Anthropology and Hugo Zeberg of Karolinska Institutet has now investigated one particularly interesting example: the Neanderthal version of the growth-hormone receptor.
Their peer-reviewed paper in Current Biology examines two amino-acid substitutions in the receptor that were characteristic of Neanderthals. The growth-hormone receptor sits on the surface of cells and transmits the signal produced when growth hormone binds to it, helping to regulate the growth of bone, muscle and other tissues.
In laboratory-grown cells, the Neanderthal form of the receptor produced a stronger response to growth hormone than the common modern-human version. Under the experimental conditions used, cells carrying it grew by about 40 per cent more, with most of the increase attributable to one of the two Neanderthal-derived substitutions.
The researchers then examined genetic and medical information from more than a million living people. Adults carrying the introgressed receptor variant had, on average, approximately 270 grams more muscle mass. They also showed subtle differences in the rear of the lower jaw and in tooth-root length—features that shifted them slightly towards the morphology seen in Neanderthals. No comparable growth effect was detected among more than 6,000 children aged eleven or younger, suggesting that its influence may become apparent later, perhaps during puberty.
The variant is unevenly distributed among modern populations. It occurs in only about 0.5 per cent of Europeans but is substantially more frequent in parts of South and East Asia, reaching frequencies of up to 24 per cent in some South Asian populations. Population-genetic evidence indicates that modern humans acquired it through interbreeding with Neanderthals roughly 47,000 years ago.
This does not mean that two receptor substitutions alone explain the characteristically robust Neanderthal skeleton. Body form is a complex product of many genes interacting with development, diet, activity and environment, and the researchers explicitly caution against attributing the entire Neanderthal physique to this one genetic variant. What the study does provide is functional evidence that a piece of Neanderthal DNA can still measurably affect the bodies of living humans.
Just as gene flow turned the evolutionary history of Hawaiian honeycreepers into a network rather than a perfectly bifurcating tree, introgression made human evolution reticulated. A genetic branch that diverged from our own did not simply terminate when the Neanderthals disappeared; fragments of it survive within modern human populations, where some remain biologically active.
For creationists, particularly those committed to a few-thousand-year-old Earth and a human population descended recently from a single founding couple, this is another awkward piece of evidence. The geographical distribution, molecular ancestry and measurable effects of the receptor variant fit the scientific account of ancient populations diverging, migrating, meeting and exchanging genes. They do not resemble the history of an independently created, unchanging human “kind”.
The human evolutionary tree, like that of the honeycreepers, therefore contains both branches and connections. Genes cross the boundaries that creationists imagine to be fixed, leaving an inherited record of encounters tens of thousands of years before their mythology says the world—or any humans—existed.
Neanderthal DNA in people today. Neanderthals disappeared as a recognisable population about 40,000 years ago, but their genetic lineage did not disappear completely. Genetic evidence shows that the ancestors of present-day humans interbred with Neanderthals, with the principal period of gene flow occurring approximately 45,000–49,000 years ago.The paper in Current Biology was accompanied by a Max Planck Society research release and a report in Nature:
As a result, people whose ancestry lies mainly outside Africa commonly carry approximately 1–2 per cent Neanderthal-derived DNA. Different individuals carry different fragments, however, so collectively living people preserve a much larger proportion—estimated at about 40 per cent of the Neanderthal genome.
Neanderthal ancestry is not entirely absent from Africa. A study published in Cell detected Neanderthal-derived sequences in every modern population it examined. Much of this appears to have arrived through later migrations of people from Eurasia back into Africa, while some apparently reflects still earlier gene flow from modern-human ancestors into Neanderthals.
Why have some Neanderthal variants survived?
The inherited fragments are not distributed evenly across the modern human genome. Many Neanderthal variants were probably neutral and survived or disappeared largely through genetic drift. Others were disadvantageous in a modern-human genetic background and were progressively removed by natural selection. Conversely, variants that helped early modern humans survive unfamiliar climates, foods or pathogens could increase in frequency.
This has left a patchwork of Neanderthal-derived DNA rather than a complete miniature Neanderthal genome within each person. Examples with measurable or suspected biological effects include:
- Immunity: Neanderthal-derived variants in the TLR1–TLR6–TLR10 gene cluster affect Toll-like receptors, which recognise components of invading microorganisms. These variants may have strengthened the defences of modern humans encountering Eurasian pathogens, although the same heightened responsiveness is also associated with an increased tendency towards allergies.
- Responses to viral disease: The consequences of introgression depend upon both the variant and the environment. One Neanderthal-derived region on chromosome 3 was associated with an increased risk of severe COVID-19, whereas a different Neanderthal-derived form of the antiviral gene OAS1 was associated with protection against severe disease.
- Pain sensitivity: Neanderthal-derived substitutions in SCN9A, which encodes the Nav1.7 sodium channel used by pain-sensing nerve cells, are associated with a lower threshold for some forms of mechanical pain. Whether increased sensitivity was advantageous to Neanderthals or early modern humans remains uncertain.
- Pregnancy and fertility: An introgressed form of the progesterone receptor is expressed at higher levels in carriers. In one large modern cohort, it was associated with less bleeding during early pregnancy, fewer miscarriages and more surviving offspring, suggesting that natural selection may have favoured it.
- Skin and hair: Neanderthal-derived DNA is unusually abundant around some genes involved in keratin filaments, important components of skin, hair and nails. This pattern suggests that certain inherited variants may have helped early modern humans adapt to conditions outside Africa, although the effects of individual variants are often complex.
- Growth and body form: The newly studied Neanderthal growth-hormone-receptor variant produces stronger signalling in laboratory-grown cells and is associated in living adults with slightly greater muscle mass and subtle differences in jaw and tooth-root morphology. It therefore provides another example of introgressed DNA retaining a measurable biological effect tens of thousands of years after it entered the modern-human gene pool.
These associations should not be interpreted as simple “Neanderthal traits”. Most human characteristics are influenced by numerous genes together with development, diet, lifestyle and environment. A variant that was beneficial in Ice Age Eurasia may be neutral—or even disadvantageous—in a modern setting.
What these fragments provide is a molecular record of population history. Their sequences, lengths and geographical distributions allow geneticists to reconstruct when human populations separated, met and exchanged genes. They show that human evolution was not the production of separately created and genetically isolated “kinds”, but a reticulated process in which diverging branches repeatedly reconnected.
Neandertal growth hormone receptor increases muscle mass in people today
Scientists describe increased activity of the Neandertal growth hormone receptor and how it shapes the bodies of people who carry it today
To the pointNeandertals were generally more strongly built than most people living today. Their bones show signs of large muscles, and they had characteristic features such as prominent brow ridges and relatively short tooth roots.
- Two Neandertal-specific changes: The study identified two amino acid changes that are unique to the Neandertal growth hormone receptor.
- Increased receptor activity: When exposed to growth hormone, laboratory-grown cells carrying the Neandertal receptor grew 40 percent more than cells carrying the more common modern human version.
- Inherited through interbreeding: Modern humans acquired the Neandertal version through interbreeding with Neandertals around 47,000 years ago. Today, it is carried by up to 24 percent of people in some parts of South Asia.
- Increased weight and muscle mass in carriers: Adults who carry the Neandertal version have, on average, about 270 grams more muscle. They also tend to have slightly shorter tooth roots and subtle differences in the shape of the jaw.
Growth hormone helps shape the body by regulating the growth of muscles and bones. It is released by the pituitary gland at the base of the brain and travels through the bloodstream. To act on a cell, the hormone must bind to a receptor on its surface, which then passes the signal into the cell.
An international team led by Hugo Zeberg of Karolinska Institutet and Philipp Kanis of the Max Planck Institute for Evolutionary Anthropology found that the Neandertal version of this receptor has two changes that are not present in the version most common in modern humans.
Neandertal variant responds more strongly to growth hormone
The study shows that laboratory-grown cells with the Neandertal receptor responded more strongly to growth hormone. They grew 40 percent more than cells with the more common modern human receptor. The researchers linked most of this stronger response to one of the two Neandertal-specific changes.
Modern humans inherited this version of the receptor through interbreeding with Neandertals around 47,000 years ago. Today, it is particularly common in South and East Asia. Up to 24 percent of people in some South Asian populations carry it, compared with around 0.5 percent of Europeans.
What struck me most was that two very different types of evidence told the same story. Cells grown in the laboratory responded more strongly, while data from more than a million people showed signs of the same effect in the body. It is rare to see laboratory and population evidence fit together so clearly.
Dr Philipp Kanis, first author.
Max Planck Institute for Evolutionary Anthropology
Leipzig, Germany.
Differences first become apparent after childhood
The difference appears to emerge only after childhood. The researchers examined body measurements from more than 6,000 children and found no link between the Neandertal version and growth up to the age of eleven. This suggests that its effects may become noticeable later, possibly around puberty, when growth hormone levels increase substantially. Among adults, people carrying the Neandertal version had, on average, around 270 grams more muscle mass.
As someone who does CrossFit, I was delighted to find Neandertal genetics and muscle mass coming together in the same study. But even a Neandertal growth hormone receptor is no substitute for training.
Miriam Berreiter, co-uthor
Department of Physiology and Pharmacology
Karlinska Institutet
Stockholm, Sweden.
The Neandertal version was also linked to subtle differences in the skull and teeth. Carriers tended to have a slightly shorter rear section of the lower jaw and shorter tooth roots. Both features are closer to what was typical of Neandertals.
It is fascinating that one genetic change inherited from Neandertals can still have an effect on the human body today. But this is only one of many genetic influences on growth and body shape. It cannot explain the Neandertal body type on its own, and it certainly does not determine a person’s overall appearance.
Hugo Zeberg, senior author.
Max Planck Institute for Evolutionary Anthropology
Leipzig, Germany.
Publication:
This study does not claim that two changes in the growth-hormone receptor can explain the entire Neanderthal physique. Muscle mass, skeletal proportions and facial morphology are complex traits produced by many genes interacting with development, nutrition, activity and environment. What the researchers have shown is more specific—and in evolutionary terms more revealing: an identifiable Neanderthal-derived receptor remains functional in living humans and is associated with measurable differences in their bodies.
The finding also provides continuity with the reticulated evolution of the Hawaiian honeycreepers. In both cases, populations diverged but did not remain permanently isolated. When their descendants encountered one another again, they exchanged genes, converting what might otherwise have been a simple branching tree into an evolutionary network. Hybridisation among birds and introgression among archaic humans are manifestations of the same natural process.
The geographical distribution of the receptor variant is part of that history. Its presence at appreciable frequencies in some Asian populations but its rarity in Europe records ancient migration, interbreeding, inheritance, genetic drift and possibly natural selection. Creationism offers no comparable mechanism capable of explaining why a functional Neanderthal-derived DNA sequence should occur in predictable patterns among living human populations.
Appealing to an undefined “human kind” does not rescue the creationist account. If Neanderthals and modern humans were supposedly different created kinds, their interbreeding and the survival of functional Neanderthal DNA breach the alleged boundary between them. If creationists instead include both within the same kind, that category must accommodate hundreds of thousands of years of divergence, anatomical change, population separation and subsequent genetic admixture. It then explains nothing that evolutionary biology does not already explain more precisely.
Nor can the evidence be compressed into the few thousand years allowed by Young-Earth mythology. The receptor entered the modern-human gene pool through interbreeding roughly 47,000 years ago, after a much longer period during which the Neanderthal and modern-human lineages had evolved separately. Its history therefore began tens of thousands of years before creationists believe the Universe was created and long before their mythical global flood.
No supernatural intervention is required at any stage. Mutation produced variation; population separation allowed lineages to diverge; migration brought them together again; interbreeding transferred genetic material; and inheritance, drift and selection determined which fragments survived. The Neanderthals may be extinct as a distinct population, but parts of their evolutionary history remain alive and biologically active in us—and our genomes bear a record that no creation myth anticipated and no appeal to magic can explain.
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