In the 21st century most people, even in academic circles, still wrongly assert that we evolved from, rather than alongside, Neanderthals. Like non-Westernised communities, Neanderthals have been subject to labelling and a whole host of false impressions simply for looking different (Devlin 2018
). They are often ridiculed as stupid brutes because of their facial features and for not having survived the evolutionary process. Yet, Nielsen et al.
) raise the possibility that Neanderthal extinction is due to interbreeding and absorption into Homo sapiens
groups, rather than an inability to out compete them or to adapt to climate change. The absurdity of the idea that Neanderthals died out as a result of limited intelligence becomes clear if one is able to envision a world where global warming has wiped out Homo sapiens
but not the cockroach.
There are historic reasons behind the previous prejudicial assumptions. At the dawn of written communication (3400-3100 BCE), there was only one living human species on Earth. No fossil record demonstrated the existence of ancestral lineages that could be traced back 9 million years ago to the chimpanzee. Any discoveries of fossils were most likely misunderstood, perhaps revered or shunned by primitive societies. Consequently, for the most part, the Homo sapiens
origins story has been subject to mythological and religious speculation with each tribe coming up with their own ideas. A great change of thinking on how humans and all other species appeared was brought about by Darwinism (Darwin 1859
). Apart from challenging the position of religion, Darwin’s Theory of Evolution provided philosophy with evidence-based arguments as to what constitutes the definition of “human” or “humanity”. His theory continues to support scientists in gaining a better understanding of Homo sapiens
, now understood to be the only surviving member of the many species that fall under the genus Homo
; Rosas 2016
3.1. The Physical Development of Intelligence
In palaeoanthropology, the exact definition of Homo
has changed over time, in line with the accumulation and reinterpretation of evidence (Wood and Collard 2001
). Wood and Collard
) suggested that for a fossil to be grouped with Homo
it needed to look more human than ape (Australopithecus
), as regards body shape and mass proportions, teeth, jaws and locomotive ability. It also required a modern human-like developmental period with respect to infant and juvenile growth into adulthood (Antón et al. 2014
). Encephalisation, the proportion of mass dedicated to the brain relative to the body (often measured by the encephalisation quotient—EQ), is also a key consideration, as it is a proxy for intelligence.
There is increasing evidence that larger brains are linked with socialisation, greater cooperative care and more complex kinship ties (Smith et al. 2012
). The EQ of Homo Sapiens
is 6.56, which puts us at the top of the list (Cairó 2011
). The Neanderthal’s (Homo neanderthalensis
) meanwhile is 4.8 (Ruff et al. 1997
). For comparison purposes the whale dolphin’s and bottlenose dolphin’s EQ are at 5.55 and 5.26 respectively. The chimpanzee, our closest living relative, has a much lower value at 2.63 (Cairó 2011
). However, some in the field have argued that for primates overall brain size and not the EQ is a better predictor of cognitive ability (Deaner et al. 2007
When one looks at brain size and development across the evolutionary transitions from Homo erectus
to modern Homo sapiens
, Neanderthals had larger average cranial capacity than modern humans, due to the neural developmental and neural organisational differences that existed between the two groups (Pearce et al. 2013
It is currently unclear whether or not Neanderthals had more or less potential for intelligence than Homo sapiens
. In fact, Rosas et al.
) show that a Neanderthal juvenile’s brain growth, had he not died, would probably have continued beyond the 7.7 years of age expected in modern humans. Slow maturation is associated with a large brain and higher cognitive abilities, which occurs in Homo sapiens
and is thus indicative of a comparable level of intelligence between the two species (Lieberman 2011
). Likewise, Neanderthals have a large endocranial volume (ECV). The average is approximately 1500 cm3
, which puts Neanderthals at the upper end of the range for anatomically modern humans (Holloway et al. 2009
). In fact, the largest Neanderthal brain size ever found is bigger than many of the brains possessed by humans walking around in the 21st century (Papagianni and Morse 2015
). This challenges any notion that Neanderthals died out because of a lack of intelligence.
From a Stoic point of view, anatomical structure would not have been enough, by itself, to classify other species as rational. They would also have required evidence of capacity for the activities they saw as distinctively rational. That said, the existence of human species similar to modern day humans, had ancient Stoics known about them, might have caused at least some philosophers to re-consider the idea that the only rational mortal beings ever to have existed were Homo sapiens.
3.2. Cognitive Ability, Language and Social Development
Apart from the physical markers of brain size and development, there are also key skills and abilities that have been used historically to distinguish humans from the rest of the animal kingdom. Of all of them, the ability to speak and construct language is perhaps the most significant and is widely seen as a quintessentially human trait.
Whilst neither archaeology nor the fossil record reveals Neanderthal cognitive functions, some research lends support to the idea that Neanderthals were capable of speech. In fact, there is a growing consensus that challenges the notion that Homo sapiens
were unique in their speech capabilities. The traditional view is still held by Noam Chomksy, who argues that there is not enough positive
evidence to suggest otherwise (Berwick and Chomsky 2015
). Some other prominent academics, such as paleoanthropologist Richard Klein, have modified their position on this question in the light of field discoveries and genetic evidence. Klein
) originally stated that Neanderthals were markedly inferior in the cognitive sense. However, in (Klein 2017
), he argued in favour of their language abilities because of their brain size, EQ and cortical configuration. Even so, he also suggested that their vowel production might be more limited and that their linguistic skills, although similar, were likely to be slightly inferior to those possessed by modern humans.
Additional anatomical evidence for Neanderthal speech relates to the position and dimension of their larynx and hyoid apparatus, which would not
have rendered them incapable of verbal communication (Boë et al. 2002
). The size of the thoracic part of the vertebral canal is also suitable (Meyer and Haeusler 2015
). This is an important factor to consider because it is one of the mechanisms that support the uniquely human ability to produce various sounds in a single breath (MacLarnon and Hewitt 2004
Speech capabilities are also evidenced on a genetic level, with both the Homo sapiens
and Neanderthal genome containing the FOXP2 gene (Krause et al. 2007
). Individuals with faulty genes of this type are known to experience speech impairment, so its existence appears to be crucial to spoken language development (Rosas 2016
). Furthermore, Mozzi et al.
) suggested that Neanderthals do not differ from anatomically modern humans when it comes to other genes associated with language, although more research has to be done before proper conclusions can be drawn. It is important to note that there is a conceptual leap between not being hindered from forming limited phrasal expressions and the ability to engage in complex linguistic communication. This needs to be considered when assessing the societal intelligence of Neanderthals (Murphy and Benitez-Burraco 2017
For communication ability, one must not only consider the vocalisation potential but also the ability to hear. Neanderthals seem to have been sensitive to wave (sound) frequencies of up to 5 Hz, which is relevant for language capacity (Martínez et al. 2004
). The ear bones of the two species are morphologically similar and the physical variations that are present are not thought to constitute a major difference between modern human and Neanderthal auditory sensitivity (Stoessel et al. 2016
An important indication of social ability is not just overall brain size but the proportion of the brain linked to cognitive tasks. Most of the Neanderthal larger brain size is linked to the visual cortex and somatic functions. Given that Homo sapiens
and Neanderthal brain size is similar, those areas dedicated to cognitive processes in Neanderthals appears comparatively reduced (Pearce et al. 2013
). The existing, albeit scant, archaeological evidence available currently supports the hypothesis that Neanderthals had weaker social skills and a lower (although certainly not limited) potential for supporting sizeable social networks of care and community (Mellars and French 2011
However, there is by no means a consensus on this matter, as there are a number of nuances. For instance, Collard et al.
) argue that the hypothesis that population size governs cultural complexity is not supported by ethnographic or archaeological findings. Collard et al.
) put forward the idea that risk proxies such as above-ground productivity and mean temperature are better predictors. Others such as Fogarty et al.
) have likewise modelled for cultural accumulation and technological innovation but have demonstrated that these are dependent on multiple factors, including those relating to the environment, cognitive ability and demographic differences.
There are field discoveries that challenge the prevailing view that Neanderthal social organisation is inferior to that of Homo sapiens
. One such example is the discovery of a Neanderthal-made karst construction of hundreds of partially calibrated, broken stalagmites (speleofacts) that appear to have been deliberately moved and placed in their current
locations, along with the presence of several intentionally heated zones
(Jaubert et al. 2016
). There have also been various archaeological findings indicative of the Neanderthal capacity to understand symbolism, including the burial of their dead and the production of ornamental paints and artefacts (Roebroeks et al. 2012
; Zilhão 2015
; Zilhão et al. 2010
). The oldest known cave art was produced by Neanderthals living in present day Spain (Hoffmann et al. 2018
; Marris 2018
). There is also sufficient evidence to show that both anatomically modern humans and Neanderthals, living during the same time-period, could create specialised tools of equal standard (Soressi et al. 2013
It is well known that Neanderthals mastered fire, as demonstrated by their regular use of it for cooking, the specific selection and collection of organic material for fire making (Esteban et al. 2017
) and fire-enabled glue production (pitch) for toolmaking. The latter requires a considerable degree of cognitive ability, technical skill and memory retention (Villa and Roebroeks 2014
). Tellingly, it is a technique that has for a long time eluded the skills of modern archaeologists, although Kozowyk et al.
) have put forward an experimentally based methodology.
Given the fossil record, we know that Neanderthal individuals survived severe injuries, illnesses and debilitating conditions. Such evidence is highly suggestive of a cognitive ability to empathise with, and take care of, members that cannot look after themselves. This behaviour does not provide what some argue is a conventional type of Darwinian advantage to the group (Cunha 2016
; Spikins et al. 2018
). One challenge to the level of symbolic thought and emphatic reasoning held by Neanderthals, relates to phenomenological considerations, including phenomenal consciousness. In other words, whilst Neanderthals did have the cognitive abilities to create art or produce certain symbolic forms, we should not automatically assume that they enjoyed their presence in the world as much as Homo sapiens
or had the same sense of wonder. In this sense, while Neanderthals may have had experiences that resemble
our feelings of empathy and aesthetic value, they could well have been less sophisticated (Montemayor and Horne 2017
). If this is true, then one must be careful when evaluating Neanderthal behaviour and ascribing it to our standard. However, others such as (Lent 2017
), view the burial of the dead by both Homo
groups as a collective sign of the “tragedy of cognition” and “metaphysical anguish”. In his worldview, these cognitive impressions are a strong indicator of one’s humanity. Regardless of the exact nature of the Neanderthal experience, all of the aforementioned activities require a reasonable level of communication, although perhaps not complex language construction (Murphy and Benitez-Burraco 2017
). Many of the latest discoveries are well summarised by Patou-Mathis
). The weight of all such evidence has clear implications for the Stoic determination of what is “human”, since this classification, for the neurotypical members of a species, is dependent on the ability to express oneself rationally either verbally or in symbolic form.
Another interesting concept from a Stoic perspective, and one which adds another level of analysis to the debate about the humanity of Neanderthals, is that of cumulative culture evolution. The latter refers to performance improvements over the long term, as shown by the societal acquisition of new or modified skills that demonstrate a level of increasing efficiency or complexity over successive generations. The process just described is experienced on an intuitive level. We take advantage of the present technologies, scientific knowledge and philosophical ideas that were only made possible by our ability to understand and make use of the imparted knowledge and artefacts of others
(Caldwell and Millen 2008
). This idea is reflected in Isaac Newton’s famous words if I have seen further it is only by standing on the shoulders of giants
). It can be explained by the educational capacities of human beings. Non-rational animals, on the other hand, while able to learn something, struggle to teach anything beyond, perhaps, the most basic of skills (Davidson 2016
). So, whilst they might have something akin to culture, they do not seem to possess anything close enough to the uniquely human organisational structure or any mechanism supportive of cumulative culture (Feldblum et al. 2018
; Tennie et al. 2009
). Therefore, the latter is a unique human ability (Osiurak et al. 2016
). It presents a clear boundary that can be drawn between humans and non-humans. It would also be, by way of extension, a key factor in determining whether Neanderthals or other archaic members of the Homo
genus could truly be considered human.
Ref. Hill et al.
) explore the many variables that need to be in place for cumulative cultural evolution to occur. First and foremost, the species, or the community, must be naturally cooperative, meaning social. The neurotypical members must also possess social cognition, regard sharing as important and have a proclivity for teaching and learning. They should also show a desire to promote equitable ideals and a willingness to punish those who break established norms, even when not directly affected by the antisocial behaviour. Kinship ties are also identified as an important mechanism for the proliferation of innovative ideas and practices of ever increasing complexity and efficiency. All of these elements mirror the natural capacity for reason and rationality, observed by the ancient Stoics who, as we have explained in the previous sections, saw human beings as naturally social with an in-built affinity for members of their own kind.
It is difficult to say for certain whether Neanderthal communities experienced cumulative cultural evolution and, if they did, at what speed and under which conditions. Hill et al.
) propose, cautiously that the level of skill required for Neanderthal tool making is indicative of their possession of cumulative culture. The speed at which this occurred might have been slower, given the smaller population numbers (Cieri et al. 2014
). Therefore, while we cannot demonstrate the level of cumulative culture to be the same as that experienced by the Homo sapiens
communities operating during the same period, we are confident that it existed to a sufficient degree to warrant the Neanderthals classification as “human”.
3.3. Interbreeding between Neanderthals and Homo Sapiens
Recent developments in palaeogenetics have demonstrated that far from Neanderthals being an ancestral species, they were very much our contemporaries (Pääbo 2014
). In fact, we can state, beyond doubt, that both species combined, and produced fertile female offspring that went on to form the modern humans of non-African origin (Sankararaman et al. 2014
). There are, for example, various hybrid fossils that display traits from both Neanderthal and Homo sapiens
phenotypes (Duarte et al. 1999
; Fu et al. 2015
). Further, the proportion of Neanderthal-derived DNA in non-Africans, at 1.5–2.1 percent of the present genome, continues to shape human evolution today (Nielsen et al. 2017
; Prüfer et al. 2014
). Another Homo
species (Denisovans), that both Homo sapiens
and Neanderthals interbred with, also continues to play a role in the evolution of the human species originating from the Australasian continent and New Guinea (Reich 2018
; Stringer 2012
). This has led to the quip that, far from experiencing the dominance of one human species over the rest, our earliest ancestors lived in a “Lord of the Rings” type world (Thomas cited by Thomas cited by Callaway 2013
The discovery that only nuclear DNA and not mitochondrial DNA (which is passed on exclusively via the maternal line) holds commonalities between Neanderthals and Homo sapiens
means that successful interbreeding only occurred between male Neanderthals and female Homo sapiens
, with male offspring rendered infertile (Mason and Short 2011
; Wang et al. 2013
). This could be used to support a non-consensual sex hypothesis (especially given the robustness of the Neanderthal physique). An identical claim can of course be made that a male Homo sapiens
could have forced himself upon a female Neanderthal, but this cannot be proven genetically. Similarly, one would not be able to demonstrate instances of homosexual encounters, consensual or otherwise. In any case, it seems quite unreasonable to assume that all sexual encounters between the different Homo
species were of the non-consensual variety. It is much more likely that at least some of the instances of interbreeding between co-existing Homo
species, including anatomically modern humans, were the result of communication and a degree of affection or appreciation. Regardless of the exact dynamics of sexual relations, we know for certain that some resulted in offspring that could claim kinship to more than one set of human species. In light of this fact, it seems that the ancient Stoics, had they known about such events, might have extended the term “human” as an umbrella classification to all such groups, not just Homo sapiens