George Christopher
Michigan, United States

Genetic sequencing, analysis of skeletal remains, and archeological studies of habitats may elucidate health challenges faced by the Neanderthals, their biological and cultural adaptations, and how their health impacts us today.

Origin, anatomy, and culture

The ancestral lineages of Neanderthals (Homo neanderthalensis) and modern humans (Homo sapiens) diverged roughly about 370,000–500,000 years ago. One lineage migrated to Europe and produced the Neanderthals, who spread across Europe and the Middle East, while the other remained in Africa and generated modern humans by about 195,000 years ago. Modern humans arrived in the Middle East 177,000–194,000 years ago and in Europe 51,700–56,800 years ago; the two species co-existed until Neanderthal extinction 30,000 years ago.¹

Whole-genome sequencing of Neanderthal remains disclosed at least 99.5% homology between modern and Neanderthal genomes.²  Interspecies mating is evidenced by a 1–4% prevalence of Neanderthal alleles in the genomes of persons of non-African descent. A comparison of Neanderthal and modern X-chromosomal genomes revealed that admixture occurred predominantly between Neanderthal men and modern women.³ However, interbreeding may have come with a fitness cost. The two species may have been poorly biocompatible; fertility of their hybrid offspring may have decreased over time.^4-6

The classical Neanderthal somatotype (long flat cranium, receding forehead and chin, prominent supraorbital ridge, midfacial prognathism, large nose and paranasal sinuses, wide thorax, sagittal femoral curvature, short distal extremities, robust bone density and muscularity) were probably adaptations to selective pressures exerted by the demands of close-contact hunting and the Ice Age climate and/or due to genetic drift.

Brain capacity was similar to or slightly larger than that of modern humans. Cranial anatomy suggests large occipital and motor cortices that may have enhanced visual and motor functions. However, Neanderthals matured faster than modern humans, which may have limited time-dependent brain development and learning. Their intellectual and linguistic capacities are debated; their use of tools and success as hunters suggests foresight, planning, cooperation, and communication. Although tool marks on skeletal remains at some sites implies cannibalism,⁷ other groups buried their dead with grave goods and produced rudimentary artistic creations. These practices suggest empathy, imagination, and the stirrings of abstraction and symbolic thought.

Neanderthals subsisted in small, isolated, inbred groups with low fecundity and high infant mortality, although some may have lived in larger and better-connected groups.⁸ They survived as hunter-gatherers and scavengers. DNA sequencing of Neanderthal dental calculus from a cave in Spain confirmed a plant-based diet of moss, pine nuts, and mushrooms,⁹ while animal bones and shells at other sites indicate that Neanderthals fed on birds; mollusks; tortoises; ungulates including rabbits, hares, deer, sheep, horses, bison, and cattle; Ice-Age megafauna such as straight-tusked elephants, wooly rhinoceroses, and mastodons; and fought predators such as cave bears, cave lions, wolves, and hyenas.

Health challenges

A genetic predisposition to preeclampsia/eclampsia has been proposed as an etiology of Neanderthal low fecundity and extinction,¹⁰ and might explain the predominantly Neanderthal male/modern female parental admixture. Although most vestigial Neanderthal gene sequences encode healthy traits, some may predispose modern humans to obesity; diabetes; dyslipidemia; hypercoagulability; autoimmune diseases including systemic lupus erythematosus, Crohn’s disease, and biliary cirrhosis; smoking behavior; and depression.^6,11 Several Neanderthal alleles encoding innate immunity are associated with severe COVID-19, while others may be protective.^12-16 The G396R variant of probable Neanderthal origin encodes a robust IgG1 antibody response to counter life-threating pathogens, but may predispose to autoimmunity.¹⁷ These findings suggest that Neanderthals may have been prone to chronic diseases and dysregulated inflammatory responses, or alternatively, that some Neanderthal variants may have been adaptive in the contexts of food scarcity, cold weather, traumatic injuries, and wound infections, but may be pathogenic among well-nourished moderns.

Neanderthal health was jeopardized by formidable environmental challenges. Equipped with spears and knives, Neanderthals relied on close-contact hunting that probably featured stabbing at short range and tackling the animal, presenting risks for mauling, bites, crush injuries, fractures, and wound infections. Butchering would have incurred risks of tularemia and brucellosis. The latter is substantiated by characteristic lesions in a Neanderthal skeleton, and could have impaired fecundity.¹⁸ Fires within cave dwellings may have caused chronic smoke inhalation that could hypothetically trigger asthma, chronic bronchitis, emphysema, carbon monoxide toxicity, and susceptibility to respiratory infections. Hypertrophic osteoarthropathy in a Neanderthal skeleton raises a differential diagnosis of chronic pulmonary disease including bronchiectasis and non-small cell lung cancer.¹⁹

The Ice Age climate would pose risks of frostbite and hypothermia. Cold weather, heavy clothing, and cave dwelling may have limited sunlight exposure and increased the risk of vitamin D deficiency. Rickets was initially proposed as the etiology of curved femurs, but seems unlikely in view of robust bone density. A 3-D morphometric landmark and semi-landmark analysis of Neanderthal, Upper Paleolithic modern, and recent modern femurs suggested that Neanderthal femoral curvature resulted from genetic drift, natural selection, or load-carrying behavior during growth and development.²⁰

Healthcare

Prolonged supportive care is evidenced by healed fractures in Neanderthal skeletons. Gas-liquid chromatographic/mass spectrometric analysis of Neanderthal dental calculus identified yarrow (an astringent); chamomile (an anxiolytic nutraceutical used today to treat irritable bowel syndrome, sleep disorders, and dysmenorrhea); and poplar bark (which contains the anti-inflammatory and analgesic compound salicylic acid); suggesting the deliberate use of medicinal plants.²¹ A Neanderthal maxilla exhibiting alveolar bone resorption and interproximal grooves on two adjacent teeth indicates the use of toothpicks to treat periodontitis.²² A Neanderthal molar displayed evidence of tooth picking and premortem dental instrumentation of a carious lesion.²³ A Neanderthal skeleton featuring atrophy of the right shoulder and proximal arm and an absent forelimb implies prolonged survival after an amputation²⁴; whether this followed trauma and/or surgical intervention is speculative.

Conclusion

Small population sizes, inbreeding, limited genetic diversity, low fecundity, high infant mortality, genetic predispositions to chronic diseases, multiple environmental challenges, and limited cultural solutions may have contributed to Neanderthal extinction. The first contacts with modern humans (who arrived with probably greater intellect and definitely more advanced technology, e.g., bows and arrows) may have initiated competition for resources and could have hypothetically imported pathogens to immunologically naïve Neanderthal populations, thus instigating epidemics of lethal diseases.²⁵ Nonetheless, the Neanderthal legacy lives on. The association of Neanderthal alleles with particular diseases may enable the identification of individuals at risk and the development of targeted interventions.¹³

References

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