The evolutionary significance of Neanderthal healthcare

In this post we present extended extracts from the very informative and interesting paper titled “Living to fight another day : The ecological and evolutionary significance of Neanderthal healthcare“, by Penny Spikins et al.

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Abstract Evidence of care for the ill and injured amongst Neanderthals, inferred through skeletal evidence for survival from severe illness and injury, is widely accepted. However, healthcare practices have been viewed primarily as an example of complex cultural behaviour, often discussed alongside symbolism or mortuary practices. Here we argue that care for the ill and injured is likely to have a long evolutionary history and to have been highly effective in improving health and reducing mortality risks. Healthcare provisioning can thus be understood alongside other collaborative ‘risk pooling’ strategies such as collaborative hunting, food sharing and collaborative parenting. For Neanderthals in particular the selective advantages of healthcare provisioning would have been elevated by a variety of ecological conditions which increased the risk of injury as well their particular behavioural adaptations which affected the benefits of promoting survival from injury and illness. We argue that healthcare provisioning was not only a more significant evolutionary adaptation than has previously been acknowledged, but moreover may also have been essential to Neanderthal occupation at the limits of the North Temperate Zone.

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Introduction Cases of apparent care for Neanderthals who were injured or suffered severe illnesses have been seen as evidence for complex cultural behaviour in these archaic hominins. However the potential evolutionary significance of Neanderthal healthcare is often overlooked.

Here we review evidence for recovery from serious illness and injury and conclude that Neanderthal healthcare was widespread, knowledgeable and effective in reducing mortality risk. We argue that healthcare, from likely short term treatment for minor injuries and illnesses as well as long term and significant accommodations, functions to reduce the risks posed by injury and illness. We situate Neanderthal healthcare within an evolutionary history of care for the ill and injured as an adaptive practice, and consider how the particular ecological challenges faced by Neanderthals may explain pressures to reduce mortality risk from injury through healthcare. We argue that rather than simply a cultural trait, healthcare can be seen as part of several adaptations which allowed Neanderthals to survive in unique environments where they lived alongside large predatory carnivores and were often dependant on large mammal biomass as a major food source. Moreover healthcare it may have been a significant factor in allowing Neanderthals to occupy a predatory niche which might otherwise have been unavailable to them.

Neanderthal healthcare as enigmatic cultural practice Evidence for remarkable survival of Neanderthals who were ill or injured has been recovered since as far back as the mid nineteenth century. The limited remains of one of the earliest Neanderthals discovered, the Feldhofer Neanderthal or ‘Neanderthal 1’ individual, discovered in 1856, demonstrated recovery with likely care from several injuries and illnesses for example. These included a severe fracture of the left arm and a healed injury to the frontal bone as well as continued survival with extensive inflammation of the paranasal sinuses and metastatic disease (Schultz 2006). Care over his lifetime may have included short term intensive care when injured, accommodation for a lack of movement in the arm in foraging for food, as well as probable care for systemic disease prior to death. He was not alone with many other Neanderthals displaying a range of severe injuries and pathologies before death. Injuries appear to have been common in these archaic hominins, and most Neanderthals appear to have suffered from some traumatic injury and recovery, often several cases of such (Berger and Trinkaus 1995; Trinkaus 2012). That Neanderthals were capable of caring for individuals who were ill or injured, from the provisioning of food, water and protection to active treatment for injuries, is widely accepted (Hublin 2009; Thorpe 2016; Trinkaus and Villotte 2017).

Perhaps the most famous individual benefitting from such care, Shanidar I, survived for at least a decade despite a withered arm, damaged leg, probable blindness in one eye and probable hearing loss through what is likely to have been daily care and provisioning from others (Crubézy and Trinkaus 1992; Trinkaus and Zimmerman 1982; Trinkaus 2014; Trinkaus and Villotte 2017). Trinkaus and Shipman comment that ‘A one-armed, partially blind, crippled man could have made no pretense of hunting or gathering his own food. That he survived for years after his trauma was a testament to Neandertal compassion and humanity’ (Trinkaus and Shipman 1993, 341). Extended periods of interpersonal care, despite a lack of any overall economic benefit to such care, is also clearly evident in other cases such as that of La Chapelle aux Saints I who suffered from several debilitating conditions, including severe osteoarthritis and systemic disease (Tilley 2015a). Tilley comments ‘it seems unquestionable that during the last months of LC1’s life, at least, the effects of these pathologies, both individually and in combination, would have constituted loss of independence – and therefore significant disability – when assessed within the Neanderthal lifeways context. The extent and impact of his pathologies suggest that LC1 needed and received health-related care provision to achieve survival to age at death’ (Tilley 2015a, 235). Most older Neanderthals have healed pathologies prompting Trinkaus and Zimmerman to comment ‘that the Neanderthals had achieved a level of societal development in which disabled individuals were well cared for by others of the social group. … Several of them, particularly Shanidar 1 and 3, lived for many years with severely disabling conditions, which would have prevented them from actively contributing to the subsistence of the local group‘ (Trinkaus and Zimmerman 1982, 75).

A broader pattern of widespread cases of recovery, survival and care Cases of recovery from severe injury or illness are often discussed in isolation. However despite a limited skeletal sample a closer consideration of the pattern of evidence for probable care reveals many cases in which recovery or survival from pathology and trauma indicate likely highly effective care from others, distributed throughout the period and spatial extent of Neanderthal occupation.

There have been debates over the precise levels of care implied by recovery in particular cases however recovery from severe illness or injury aided by care seems relatively common. As well as other cases, fractures to the main weight bearing bones of La Ferrassie 1, and La Ferrassie 2 are likely to have entailed care from others to ensure recovery, whilst a break or sprain of the left foot of Shanidar 3 is also likely to have entailed support as would the recovery from serious cranial injuries seen in St Cesaire 1 and Krapina 37. In several cases healthcare or support is likely to have been long term, with severe periodontal inflammation likely to have restricted the capacity of Aubesier 11 and Guattari 1 to forage for themselves, and serious arm injuries likely to also make foraging (and certainly hunting activities) difficult for the Feldhofer Neanderthal (Neanderthal 1), Krapina 180 and La Quina 5. Healthcare also seems likely to have been knowledgeable and remarkably technically competent in Neanderthals. In the case of La Chapelle aux Saints 1, for example, care when most debilitated is likely to have included fever management, hygiene maintenance and repositioning and manipulation (Tilley 2015a). Individuals with systemic diseases (such as La Chapelle aux Saints 1) would have needed to have been kept hydrated to manage fever, whilst those with severe wounds and fractures would have required adequate nutrition and rest. A femoral fracture at the greater trochanter of La Ferrassie 1 for example would have been painful and severely restricted mobility requiring care and provisioning (Fennell and Trinkaus 1997), as would chronic osteomyelitis of the hip in La Chapelle aux Saints 1 (Tilley 2015a). High rates and healing and low rates of infection suggest that some form of wound management may have been common (Trinkaus and Zimmerman 1982, 75). This may have involved using particular dressings and means of reducing blood loss. Ochre may potentially have been used as an antiseptic when applied to wounds (Zilhão et al. 2010; Velo 1984). There is also evidence for use of the use of medicinal plants in dental calculus (Hardy et al. 2012; Hardy 2018), including poplar, which contains salicylic acid and may have been used as a painkiller (Weyrich et al. 2017).

Neanderthals appear to also have been expert collaborative healthcare providers. Moreover, the visible archaeological evidence is likely to be the ‘tip of the iceberg’ of more common healthcare practices, the majority of which remain invisible to archaeological interpretation.

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Occupying challenging environments in the North Temperate zone Neanderthals occupied what was at the time a northernmost extension of archaic human occupation, being present in Western Eurasia from approximately 250ka BP (Marra et al. 2017). Securely dated evidence for Neanderthal occupation stretches as far north as 55° N (Finlayson and Carrión 2007; Slimak et al. 2011; Nielsen et al. 2017) although highly debated Mousterian assemblages have been found as far north as near the Arctic Circle at Byzovaya (Slimak et al. 2011). As descendents of earlier european Homo heidelbergensis and pre-Neanderthal populations Neanderthals were not the first hominins to successfully occupy Western Eurasia but they nonetheless occupied the most northerly regions.

In general ecological terms as environments become cooler, more seasonal and often more arid with increasing latitude (or altitude, or effective latitude during glacial phases), survival becomes increasingly dependant on abilities to cope with the challenges imposed by the environment rather than biotic interactions. Both intra and interspecies competition is affected by this latitudinal gradient (Schemske et al. 2009). Thus survival depends on managing and mitigating the notable risks which these environments bring, particularly at the most northerly limits of occupation and during glaciations where effective latitude (in terms of cold and aridity) increases. With increasing latitude resources become more variable seasonally, increasingly patchy and less reliable placing a challenge on hominin occupation (Pearce et al. 2014). Risks to mortality and survival come from several different sources. There are risks to effective reproduction posed by seasonal variations in the resources needed to support pregnancy and lactation for example, variable resources leading to potential famines, extremes of cold which can threaten infant survival, as well as high requirements for mobility to exploit more patchy resources. Dependence on animal food for survival increases with increasing distance from the equator (Johnson 2014), and moreover average prey size increases with cold and increasing latitude (Rodríguez, Olalla-Tárraga, and Hawkins 2008) bringing elevated risks of injury and mortality through injury from hunting as well as through competition with other predators.

The highly seasonal, risky and unpredictable nature of Late Pleistocene environments presented major ecological challenges for human communities. Palaeoecological evidence documents a notable instability in European temperatures, with several harsh climatic events concurring to create a notable deterioration of an already severe glacial environment (Sánchez Goñi et al. 2002; Moreno et al. 2014). During the Last Glacial period a series of Heinrich events, during which large icebergs traversed the North Atlantic causing global climate cooling, followed by rapid warming episodes (ie Dansgaard-Oeschger events) caused abrupt alternations of cold-arid and warm-humid environments. Moreover extended and independent phases of regional drought with significant repercussions on Neanderthal populations have been documented (Luetscher et al. 2015; Wolf et al. 2018). Climatic and ecological challenges at less than millennial scale had a substantial impact on Neanderthal communities during MIS 3, affecting the availability of food resources, changing distributions of plant and animal communities, and forcing costly and repeated mobility and changes in dietary habits (Hodgkins et al. 2016; El Zaatari et al. 2016). Furthermore there were notable contractions of occupation from north and east Europe and into a few regions with milder climates including southerly Mediterranean refugia (Finlayson et al. 2006; Stewart et al. 2010). There was also a significant fragmentation of Neanderthal distribution and demographic decline in Europe with frequent regional extinctions (Dennell, Martinón-Torres, and Bermúdez de Castro 2011; Sánchez-Quinto and Lalueza-Fox 2015; Hublin and Roebroeks 2009; Benito et al. 2017; Wolf et al. 2018) and sporadic population replacement (Fabre, Condemi, and Degioanni 2009; Dalén et al. 2012; Melchionna et al. 2018; Hajdinjak et al. 2018). The unreliability of food resources will have also affected populations in other ways. Evidence for nutritional stress from enamel hypoplasia amongst Neanderthals is common and within the upper range of that observed within modern hunter-gatherers for example (Ogilvie, Curran, and Trinkaus 1989; Guatelli-Steinberg, Larsen, and Hutchinson 2004; Hlusko et al. 2013). Furthermore contacts between groups may have been limited by low population density (see Dennell, Martinón-Torres, and Bermúdez de Castro 2011; Bocquet-Appel and Degioanni 2013; Sánchez-Quinto and Lalueza-Fox 2015; French 2016; Simons and Sella 2016; Hajdinjak et al. 2018), driven by low plant productivity and animal biomass, and the energetic costs of movement across large areas of landscape. Low population densities and limited contacts also explains low rates of introgression, with half sibling matings being common (Prüfer et al. 2014; Castellano et al. 2014; Rogers, Bohlender, and Huff 2017; Harris and Nielsen 2016).

Some Neanderthal populations undoubtedly occupied relatively stable and productive ecological regions, particularly in Mediterranean contexts, however for many this was survival ‘on the edge’. Although the arrival of anatomically modern humans has been suggested as one obvious possible factor in eventual Neanderthal demise (d’Errico and Sánchez Goñi 2003; Hortolà and Martínez-Navarro 2013) and it may have been precisely the challenges posed by climate and environmental changes which were ultimately the most significant influence (Finlayson et al. 2004; Stewart 2007; Müller et al. 2011/2; Melchionna et al. 2018) or at least a combination of several factors including within them environmental and ecological changes (Rey-Rodríguez et al. 2016). The contemporary extinction of around 35-40% of co-existing megafaunal species in particular supports the argument of a primary role of environment in Neanderthal decline (Stuart and Lister 2012) with Neanderthal populations eventually dying out in most of Europe between 35-40 ka BP (Higham et al. 2014; Hublin 2017) and ultimately in Iberia (Finlayson et al. 2006).

Biological and anatomical responses The effects of selection pressures from challenging environments on Neanderthal biology and anatomy are well accepted. High endurance requirements and frequent famines influenced their body shape, proportions and physiology for example.

Furthermore cognitively Neanderthal’s large visual cortex may also be an adaptation to selective pressures on identifying and hunting animals in conditions of potentially low visibility (Pearce, Stringer, and Dunbar 2013).

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Adaptive subsistence practices Neanderthals also adapted their subsistence practices to the ecological contexts, with Neanderthal diets widely acknowledged as reflecting their ecological circumstances. Neanderthals occupied regions with substantial ecological variation in time and space, and varying their diets accordingly (Fiorenza et al. 2011; El Zaatari et al. 2016). Though famously characterised as hunters of big game Neanderthal diets were clearly far more complex and variable. Plant foods appear to have been exploited as and when available and are likely to have formed some component of diets throughout the region occupied (Henry, Brooks, and Piperno 2011; Power et al. 2018). Coastal populations would have been able to rely on less risky marine and intertidal resources, as seen at Gibraltar in the exploitation of shellfish and seals (Cortés-Sánchez et al. 2011). Fish and birds are also likely to have been exploited when available (Hardy and Moncel 2011). In some Mediterranean regions, particularly in interglacial periods, it would even have been possible to depend significantly on plant resources (Salazar-García et al. 2013), and Neanderthals appear to have particularly flourished in these environments (Benito et al. 2017). At El Sidron the dietary profile from dental calculus suggests that a notable component of plant foods contributed to Neanderthal diets for example (Weyrich et al. 2017; Estalrrich, El Zaatari, and Rosas 2017). Neanderthals in Mediterranean contexts provide the only known cases of dental caries due to ingestion of carbohydrates in the form of plant resources (Walker et al. 2011).

There is however good evidence for a heavy dependence on a largely meat based diet in most regions alongside behavioural adaptations to a dependence on large mammals for subsistence. Stable isotope studies (Bocherens et al. 2005; Richards and Trinkaus 2009; Naito et al. 2016), molar macrowear (Fiorenza et al. 2011; El Zaatari et al. 2016; Estalrrich, El Zaatari, and Rosas 2017) and faecal biomarkers (Sistiaga et al. 2014) suggest that Neanderthals outside of the Mediterranean region depended on a largely meat based diet. Faunal remains on archaeological sites also suggest a reliance on large game, which varied according to the ecological context, with bison, reindeer and horse predominating within faunal assemblages (Smith 2015), though Neanderthals also exploited megafauna in the form of woolly rhinoceros and mammoth, such as at La Cotte de Ste Brelade (Scott et al. 2015). They were clearly well able to adapt to the different opportunities which large game provided, sometimes hunting individual animals, and at other times focusing on herds, including the hunting of prime age individuals.

That the pressures of reliance on meat from large game animals were a pressing adaptive problem in many regions is clear. Whilst plant foods and other resources were undoubtedly a component of diets everywhere, meat as the dominant resource outside of the Mediterranean region, and probably to the most extreme degree in late winter and early spring imposes physiological challenges. In open environments, as recorded at Spy, Neanderthals survived on a largely carnivorous diet for example (Weyrich et al. 2017; Estalrrich, El Zaatari, and Rosas 2017). A high protein diet can have serious physiological consequences. Selective pressures to adapt to the strains imposed by a high protein diet has also been argued to be the explanation for the large lower thorax of Neanderthals (Ben-Dor, Gopher, and Barkai 2016).

Individual and group survival clearly depended on capacities to adapt to notable ecological challenges, and to find ways to reduce risk, with healthcare practices best seen as part of these wider patterns of adaptation.

Subsistence related mortality risks Selective pressures to reduce mortality risks through healthcare provisioning come most obviously from the demands of common subsistence practices.

Given most available biomass being in the form of large herbivores in many regions (Daura et al. 2017) a common reliance on hunting large game would clearly be an inevitable part of Neanderthal adaptation in most regions. Requirements for high levels of mobility driven by relying on highly dispersed game (Laura Niven et al. 2012) bring risks of injury in itself, alongside simply moving across difficult terrain (such as when hunting ibex, (de los Terreros et al. 2014; Yravedra and Cobo-Sánchez 2015). However it would have been Neanderthal hunting methods which brought particular injury risks. Close range hunting with wooden or stone tipped spears seems to have been the norm given environments in which ‘running down’ prey through heat exhaustion would not have been a feasible strategy (Rhodes and Churchill 2009; Shea and Sisk 2010). Whilst hunting of any animal prey is dangerous, however close encounter hunting of large game demands a high level of collaboration and brings particularly high injury risks (Gaudzinski-Windheuser et al. 2018). Evidence from characteristic impact patterns on fallow deer at Neumark-Nord during the last interglacial confirms the use of close range spears (Gaudzinski-Windheuser et al. 2018). A combination of thrusting and close range throwing seems the most likely hunting technique as Neanderthals would have been physically capable of using thrown projectiles (Roach et al. 2013). Repeated throwing behaviour is also the most likely explanation humeral abnormalities in a Neanderthal from Tourville-la-Riviere.

The elevated injury rates from close range hunting compared to the use of long range projectiles is evident in ethnographic and archaeological contexts. The megafauna present during Neanderthal occupation, including mammoths and woolly rhinoceros would be particularly dangerous prey, easily able to overcome an individual human assailant.

Besides direct confrontations with prey Neanderthals also faced the presence of large carnivores which in turn were dangerous as competitors and as predators. Conflicts with such predators were extremely dangerous and could lead to death or severe injuries.

Interactions between hominin and large carnivores will have occurred in a variety of contexts, and across the whole range of Neanderthal occupation, not only through competition for resources, but also potential occupation sites in caves.

Neanderthals occupied cave sites also favoured by carnivores, with faunal accumulations in these locations deriving from both (Rufà et al. 2017). Cave bears often occupy caves also frequented by Neanderthals.

Theoretically at least the distribution and character of injuries across the skeleton may be a potential source of evidence for the relative injury risks from different activities. A greater prevalence of injuries to the head and upper body in Neanderthal skeletal material appeared to be similar to that seen in adult rodeo riders and supported an interpretation of the majority of injuries being sustained through direct engagement with large and dangerous prey (Berger and Trinkaus 1995). This interpretation remains debated however (Trinkaus 2012). Different physiologies make such comparisons difficult, particularly as the injury profile in adolescent rodeo riding is notably different (Stoneback, Trizno, and Albright 2018). Furthermore similar injury profiles also characterise pathologies in skeletal remains throughout the Pleistocene (Wu et al. 2011) suggesting that differential preservation may be a more likely explanation for this pattern.

The extent to which any particular individuals may have been protected from the mortality risk imposed through hunting large game and competing with large carnivores, or indeed differentially exposed to such risks, also remains unresolved.

Mortality risks from interpersonal violence Further mortality risks may have been driven by interpersonal violence. Lethal interpersonal violence has been recorded in pre-Neanderthal populations at Sima de los Huesos where cranium 16 shows evidence of several blunt force trauma blows to the frontal bone for example (Sala et al. 2015). For Neanderthals themselves there are two recorded instances of probable interpersonal violence, one individual from St Cesaire (Zollikofer et al. 2002) and one from Shanidar (Shanidar 3) (Churchill et al. 2009b). The former suffered a blunt force head wound (from which they recovered) and the latter a projectile point injury, most probably from modern human projectiles, which appear to have led to death several days later. Interpersonal violence has also been argued to be the most likely explanation for patterns of cranial trauma at Krapina (Estabrook and Frayer 2014) although other instances of potential interpersonal violence are more ambiguous.

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The influence of Neanderthal behavioural ecology A certain ‘ratchet effect’ of increasing dependence on healthcare driven by Neanderthal behavioural ecology may have also have come into effect. Most obviously Neanderthal robust body sizes and high energy requirements (Churchill 2014) will have placed additional pressures on ensuring adequate resources through hunting success. These same high energy requirements will also have limited group sizes and so increased interdependence, and the significance of any individual mortality to survival. Evidence from El Sidron of a group apparently made up of around thirteen individuals, three related males, four females, three adolescent boys and three infants is one potentially good example (Lalueza-Fox et al. 2011). The loss of even one adult hunter in such a circumstance may be enough to make any such group vulnerable, whilst their high relatedness would act to increase the selective advantages of helping others in the group. High levels of relatedness, with half sibling matings common (Prüfer et al. 2014), also brings with it other pressures on healthcare provisioning. Low genetic fitness, caused by high levels of inbreeding (Sánchez-Quinto and Lalueza-Fox 2015; Simons and Sella 2016) brings higher incidences of pathologies which are likely to have required care and support (Dean et al. 2013; Juric, Aeschbacher, and Coop 2016; Simons and Sella 2016).

A particular dependence on the high levels of skill and the technological competence required in acquiring difficult resources in colder and more seasonal environments (Bamforth and Bleed 1997; Bleed 1986) will also have increased the advantages of survival of older and even partially disabled group members to Neanderthals. Hunting efficiency, and thus resource acquisition, increases with age in modern hunter-gatherer contexts even where prey are not particularly dangerous (Walker et al. 2002), and this ‘learning curve’ is likely to have been even steeper for Neanderthals, particularly where variable environments also adds to the relative advantage of knowledge built up over long periods. The knowledge, skills and experience required both in healthcare in general and in care related to assisting births, and keeping babies and infants alive in cold conditions should also not be underestimated. By extending life expectancies through healthcare following injuries the group knowledge and experience of how to deal with many different challenges, particularly in difficult or unusual circumstances, will have increased. Moreover any increased dependence on the knowledge of older members with the greatest life experience will have made care practices all the more necessary to survival.

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The wider evolutionary significance of healthcare provisioning Healthcare provisioning affects the ecology and evolution of hominins, as perhaps seen most clearly in Neanderthals. It might be tempting to further conclude that these archaic humans further displayed some kind of cognitive adaptation to a high risk, high injury niche. Genes regulating dopamine production, and influencing patterns of risk taking, have been influenced by patterns of Palaeolithic migration (Chen et al. 1999; Matthews and Butler 2011) and even historical subsistence practices (Kidd, Pakstis, and Yun 2014) for example. However a broader perspective on pro-social behaviour would instead suggest that pro-sociality has been integral to human adaptation from much earlier periods, with substantial behavioural plasticity of pro-social behaviour according to context being part of that adaptation (House et al. 2013; Rajhans et al. 2016). In modern contexts high risk environments increase propensities to altruism through normal behavioural plasticity according to context (Li et al. 2013) as does dependance on collaborative hunting of very large and dangerous game (whale hunting, (Heinrich et al. 2004). In cognitive terms, Neanderthal’s willingness to care for injured and ill group members most likely reflects simply that they were humans coping with the particular challenges that their lifestyles entailed.

The longer evolutionary history of healthcare provisioning is nonetheless likely to have influenced the path of human evolution in various different ways (Bastir 2018). Healthcare can have a direct effect, such as in the relationship between foetal brain size and pelvis shape in Neanderthals, implying a characteristic half turn of a foetus at birth which is unlikely to have evolved without assisted births (de León et al. 2008). However even provision of moderate care can influence the selective advantages and disadvantages of genes linked to several traits, such as local adaptation of the TRPM8 cold receptor gene with increasing latitude, which whilst protecting from effects of cold is also associated with migraine susceptibility (Key et al. 2018). Care can also have subtle and complex effects of selection pressures, such as pressures to be pro-social and affiliative (Hare 2017), or to express subtle indicators of friendliness and vulnerability (Godinho, Spikins, and O’Higgins 2018). Positive selection for autism genes may also imply a level of social support for those who bring additional skills but may need more support (Spikins, Wright, and Hodgson 2016; Polimanti and Gelernter 2017). Healthcare provisioning is likely to have affected many realms, from anatomy to physiology to cognition and further research might help us to understand these wider evolutionary implications of healthcare provisioning both in Neanderthal populations and beyond.

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Research-Selection for NovoScriptorium: Maximus E. Niles

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