Introduction

Neanderthals have lived between 800 kya to 30 kya in Eurasia, occupying many territories. Figure 1 shows their extension in Eurasia. They have lived through various Marine Isotope Stages (MIS, which are paleoclimate periods deduced from oxygen isotopes) that have recorded numerous climatic fluctuations (See Figure 2). The affiliation of different hominin species' occupation of Eurasia from MIS 20 is debated, with early European occupations by Homo Antecessor, to northern expansion by possible Homo Heidelbergensis in 500 ka (Ashton and Lewis, 2012). The Sima de los Huesos MIS 12 individuals have been debated to be either early Homo Neanderthaliensis, finding similarities with the MIS 13 evidence in Boxgrove, UK (Lockey et al., 2022) , or a different taxon but with common descendants (Arsuaga et al., 2014).

Figure 2. Graph of mean temperatures from MIS 1 to MIS 19. Adapted from Hughes et al. 2020.

Palaeoecological reconstructions suggest Neanderthals occupied several cold and low-temperature climates. Candy et al. (2015) explore Britain's occupation during MIS 13 and recognise paleoenvironmental data suggesting cool climates, at lower temperatures than present, with winters well below freezing. Neanderthals inhabited sites well below their naked tolerance, according to measurements of Aiello and Wheeler (2003). Northern Europe occupations reveal the most extreme temperatures sustained during most glacial and interglacial periods (Bertran et al., 2016). MIS 4 and 3 are the coldest and most unstable millennia Neanderthals ever endured (Gilligan, 2007; Wales, 2012; Melchionna et al., 2018; Niekus et al., 2019), with possible winter temperatures reaching as low as -27° C in Northern Europe (Van Andel et al., 2003). Table 1 presents some of the coldest temperatures recorded at sites from older evidence of occupation of northern Europe (MIS 13) to the last period (MIS 4-3).

Table 1. Winter temperatures of selected sites from older evidence of hominin in northern Europe to the last period of occupation of Europe.

Neanderthals have long been associated with cold climate adaptations, as they lived during various glaciations (Howell, 1952). Many physiological aspects have often been associated with cold resistance. This is not as certain when counterarguments are considered, which debate these adaptations in the first place or devise other explanations for their presence.

A stockier physiology and shorter limbs have been argued to dissipate less heat (Bergmann, 1847; Allen, 1907). Pomeroy et al. (2012) and Bogin et al. (2022) have revisited this notion claiming these facts are unreliable when health, nutrition and diseases are factored in during development. These characteristics have also been linked to forestal mobility adaptation (Stewart, 2005). Thicker bones, while possibly indicative of greater muscle mass and hence greater insulation (Mariotti and Belcastro, 2011), could also depend on hormonal anomalies (Maureille and Bar, 1999) or greater energetic and physical activity requirements (Shaw and Stock, 2013). Many suggestions have also been made for other characteristics often associated with cold resistance such as enlarged nasal cavities (Rae et al., 2011 for alternative argument), higher Basic Metabolic Rate (BMR) (Longman et al., 2022 for alternative argument) and a larger thorax (Ocobock et al., 2021 and Ben-Dor et al., 2016 for alternative arguments). These alternative arguments do not necessarily negate the fact that Neanderthals could be better adapted to survive cold climates. They want to illustrate that some characters cannot be solely explained as cold adaptations. A recurrent observation made by these authors is that biological adaptations are mostly related to high-intensity activities, consuming greater energy in shorter but more powerful actions. Hence, Neanderthals' biological adaption to cold environments should not be unambiguously assumed. This is further sustained by the notion that thermoregulation is dependent on many aspects that are not visible archaeologically, such as hair coverage (Dàvid-Barrett and Dunbar, 2016), body fat, muscle mass and Brown Adipose Tissue values (BAT) (Steegmann et al., 2002; Snodgrass and Leonard, 2009) and resistance to the cold from exposure in developmental phases (Hrdlicka, 1945; Jones, 1972).

As cold adaptations are fundamentally still unclear, there are debates surrounding temperature resistance. Collard et al. (2016) suggests a minimum temperature of 1 to 2.5° C lower than humans. Aiello and Wheeler (2003) estimate a limit of 6.5° C for Neanderthals, against 10° C for Sapiens. Hosfield (2020) argues for a 7.6° C value for a naked Neanderthal. There is no definite agreement on specific temperature values, however, most models oppose an extreme difference between Sapiens' and Neanderthals' naked tolerance.

It is also important to consider demographic variations, as some physiological models are based solely on male values (e.g. Aiello and Wheeler, 2003). Males and females have different temperature resistance because they have different BMRs (Rodríguez et al., 2021). Trinkaus (1980) suggests Neanderthals had greater sexual dimorphism than Sapiens, hence BMR and temperature endurance could have been even more disparate between biological sex, rendering females more susceptible to lower temperatures. Children are also more vulnerable to the cold as they have more gracile skulls - Neanderthals presenting parallel growth to Sapiens (Tillier, 2011) - and BMR decreases with age, hence elderly individuals are more susceptible to low temperatures than the young male population (Luo et al., 2018).

In summary, Neanderthals' biological adaptability to the cold is not to be taken for granted. This research considers Neanderthals were not immune to the dangers of cold temperatures. Frostbite, hypothermia, and cell damage are common complications of exposure to low temperatures that can lead to permanent damage or death (Cheung, 2015; Daanen and van Marken Lichtenbelt, 2016). Neanderthals would have been particularly susceptible to sinusitis and otitis because of their skull and inner ear conformation (Trajer, 2023), thus lower temperatures exacerbated these risks. Moreover, this is increased for vulnerable demographic groups: elderly, children, ill and pregnant women.

Archaeological evidence - Cultural insulation

As well as possibly being biologically susceptible to low-temperature environments, the archaeological record is fundamental to understanding Neanderthals' cultural practices adopted to survive certain climatic challenges. Records of fire and shelter uses are available; however, they present biases that limit the understanding of the evidence (Ocobock et al., 2021; Rodríguez et al., 2021) and they are not sufficient insulators when individuals are away from settled camps (White, 2006; Gilligan, 2010). That is why the focus of cultural insulation practices is placed on clothing.

Clothing traps warm air, insulating the body in colder external temperatures (Soresen, 2009). A 'Clo' unit, roughly corresponding to one layer of coverage, is used to indicate clothing thermal resistance (Gagge et al., 1941; Sloan, 1979). Authors have tried to determine Neanderthals' Clo requirements in relation to the inhabited environments (e.g. Gilligan, 2007; Wales, 2012). Secondary strands of evidence have been utilised to deduce clothing manufacture in Neanderthals for example: the exploitation of faunal resources (Cervidae) ( Collard et al., 2016; Martisius et al., 2020), genetic lice evidence (Li et al., 2010; Ocobock et al., 2021), tooth wear and tools for leather manufacturing and possible hide curing purposes (Soresen, 2009; Soressi et al., 2013; Heth, 2015), hide curing (Koller and Baumer, 2010; Rots et al. 2015 - desiccants). The greater debate concerning Neanderthals' clothing stands in the evidence for simple or complex clothing. Simple clothes are wrapped around the body with strings and not sewn. Complex clothes are more specialised and involve sewing. For this reason, they are recognised after the appearance of specific tools that are classed as 'mode 4 technology' (with cutting, scraping and piercing tools) and the presence of eyed needles (Gilligan, 2007). They first appear in association with Sapiens in parts of North and South Africa during colder episodes (Gilligan, 2007).

Anatomical differences in Neanderthals' hands compared to Sapiens reveal a more powerful rather than precise grip, hence some argue this would have impeded the act of sewing and handling small objects (Bardo et al., 2020; Ocobock et al., 2021). Wales (2012) models a prediction for the percentage of covering required for Neanderthals in various habitats in different periods. He claims that tailored clothing is necessary only above the 93% body coverage needs. The models presented (See Figure 3) place Neanderthals into a maximum of 80-90% of body coverage according to site evidence, hence rejecting tailored clothing as a requirement. Additionally, he argues that hunter-gatherers can obtain sufficient body coverage (80%) and survive without tailored clothing as the Jaralde and other Australian groups can prove.

Wales' arguments fail to consider two aspects. First, body coverage needs are higher for more vulnerable sections of the populations (as illustrated above) - ill and injured, children, elderly and pregnant women - thus tailored coverage might have been required where Wales' (2012) models predict 80-90% coverage. Secondly, the Jaralde are not an exemplar of Neanderthals' lifestyles, as they relied on hunting with long-distance projectiles, in particular spear throwers (Berndt, 1940). Neanderthals relied on hunting at close quarters, such as ambushing megafauna (Marín et al., 2017) as is evident from the non-extensive projectile technology and the common skeletal evidence for trauma and injury (Hosfield, 2016; Ocobock et al., 2021). Moreover, cutting and piercing technology, retained necessary for complex clothing and being mostly affiliated with Sapiens, and the more specialised tools such as blades and needles appearing from the Gravettian/Aurignacian (Gilligan, 2007; Collard et al., 2016), are visible for Neanderthals as well - Lithic and bone awl-like points to pierce hides and blade-like tools (Soresen, 2009). One piece of evidence for fibre technology has been recently discovered at Abri Du Maras, which attests to Neanderthals' knowledge and capacity to obtain fibre strings. Hand sewing and alternative needles (pine needle or small bone fragments) are also considered as possible sewing techniques (Soresen, 2009; White, 2006).

Lack of knowledge - wet environments

Biological and cultural adaptations have so far focused only on survival in cold climates. Most research lacks attention to the dangers that not only cold but also wet environments pose to the physiological limits and clothing technology of Neanderthals. Wet clothing annuls clothing insulation, thus invalidating its protecting properties and conducting to more rapid body heat dissipation (Golant et al., 2008; Hagen et al., 2024). Wet environments, therefore, increase substantially the risks of hypothermia and frostbite (Kuklane et al., 1998). Wet environments also create a problem in finding reliable dry fuel, essential for drying and keeping warm. When discussing palaeoecology, it is important to consider snow, precipitation and humidity factors. To understand that Neanderthals were effectively living, moving in and navigating zones affected by the risk of wet and cold, Trajer (2023) proposes an overview of biome occupations of Neanderthals through time (See Figure 4). Biomes are good indicators that consider multiple aspects of the environment - temperatures, precipitation, windchill, fauna and flora (Trajer, 2023). Site presenting biome forest environments can be good indicators of climates affected by higher precipitation values to lower temperatures (list of sites in Appendix 1).

In summary, it is considered here that Neanderthals could have engaged in such strategies, even if there is no direct archaeological evidence. Wet environments would exacerbate cold-related complications. Neanderthals did inhabit environments that would pose the risks of the cold and wet, thus they are likely to have developed strategies to counter such dangers. Evidence for the care of more vulnerable groups such as elderly and pregnant women, and for recovery of the ill and injured, attests that, in these environments, risks were acknowledged and contrasted.

Materials and Methods

Methods

The following research will, first, devise a possible waterproofing strategy, utilising materials and technologies available to Neanderthals, inspired by ethnographic accounts of waterproofing activities in modern mid-to-high-latitude hunter-gatherers. These have been collected from a search of the eHRAF World Cultures Database with the following key words: 'adhesives'; 'rain gear'; 'snowshoes'; 'waterproof'; 'specialised clothing'. Following this, an experimental strategy to test the waterproofing capacities of the materials selected will be conducted. The results will evidence the success rates of various materials. The discussion will investigate the implications of waterproofing efforts in technological complexity, activities, and social dynamics.

Ethnographic sources

A review of 68 ethnographic accounts of mid-to-high latitude small-scale groups of hunter-gatherers has been conducted (a summary of the strategies divided into categories in the Appendix 2). The results show that groups would select either specific animal skins or plant-based resources for their more water-resistant properties to fashion clothing items (ponchos, hats, capes, mittens, jackets, leggings). For more specific applications, some groups utilise natural adhesives (named 'pitch', 'tar', 'resin') as waterproofing agents. These are often applied on shoes, cordage made for bow strings or stitched seams to prevent the seam from opening (e.g. Chippewea, Pomo, Inuit: Densmore, 1929; Barrett, 1952). The experiment here developed will investigate the possible waterproofing qualities of different adhesive admixtures in relation to fitted, complex clothing.

Experiment and Materials

Rationale for materials

As discussed, plausibly manufactured by Neanderthals, this experiment fashions fitted clothing. The inaccessibility of non-eyed needles in the archaeological record and the power-grip type of hand morphology suggests the use of hand-sewing for tailored seams. There is direct and secondary archaeological evidence to understand possible Neanderthals' strings and cordage manufacture. Hardy et al. (2020) revealed the discovery of a single evidence of cordage technology made of plant fibres (bark). Ethnographic sources reveal that Nettle stalk stems and deer or reindeer sinew are efficient materials for making string (Chippwea, Inuit: Densmore, 1929; Oakes, 1991; Saami: Anderson, 1978; Copper Eskimo: Diamon, 1946; Pomo: Barrett, 1952). Nettle is very common and can be easily found in many environments (Plants of the World Online, 2024) including boreal forests cold climates, hence available to Neanderthals even in harsher conditions. Deer/reindeer sinew and hide would be available, as specimens from Cervidae families represented a great part of Neanderthals' faunal exploitation (Collard et al., 2016). The rationale behind the choice of adhesives is suggested by ethnographic accounts (above) in combination with archaeological and experimental evidence. Experiments have aimed to grasp possible Neanderthals' understanding of adhesives' material properties. Natural adhesives (birch bark tar, beeswax and pine resin) have been a stable component of Neanderthals' behaviour at least from MIS 7 until MIS 3 (Mazza et al., 2006; Degano et al., 2019). These adhesives would all be available in boreal forest environments (Encyclopedia Britannica, 2024a; USDA Forest Service, 2024).

Methods of extraction of beeswax can imply climbing or felling branches of trees to collect the honeycomb and then filtering the wax from the honey (Turnbull, 1965; Heinen, 1973). It can imply a level of fire control to boil and cook the wax (Holmberg, 1950). Honeybees are found in many biomes; however, they retreat in their hives at temperatures below 10° (Encyclopedia Britannica, 2024b). Therefore, although honey and honeycomb are available, they might be less visible and active during winter or colder periods.

Experiments have revealed that tar can be extracted from a roll of bark of birch trees exposed to a 300-350° C fire, with careful fire management and constant attention (Schmidt et al., 2023). Schmidt et al. (2023) reveal that producing and treating birch bark tar required time and great attention to the heating procedure, as few minutes and lower/higher temperatures could significantly impact the quality of the adhesive. Kozowyk and Poulis (2019) conclude that tar presents better working properties and is more versatile than resin, hence it might have been preferred to the quicker, and easier-to-extract, resin. Kozowyk et al. (2016) conclude that beeswax, as a bonding agent, significantly improves the quality of the adhesive, having a plasticising effect. Considering this literature, this experiment will test the waterproofing properties of these different adhesive admixtures on the sinew and nettle seams.

Experimental design

Birch bark tar as a fabric glue, in combination with various additives, has been tested by Baker et al. (2021), who concluded that it is not suitable to glue pieces of fabric together and hold the stress of movements. This research explores a novel strategy that opts for the use of tar not as sole glue but as a resistant glue and waterproofing layer in combination with seams, as attested by ethnographic sources. The experiment consists of joining two pieces of leather together, as possibly required for joining the ends of a cape to the neck, joining the sides of mittens or limb covers. It utilises deer leather (with no fur, as it would complicate the sewing process) processed in traditional methods (rhubarb root as a tanning agent), nettle and sinew as threads and birch bark tar (BBT), pine resin (PR) and beeswax (BW) as adhesives. A process of pre-testing is used to determine the most valuable percentages of admixtures for the experiment, illustrated in Table 2.

Table 2. Adhesives quantities used in the experiment.

Experimental procedure

Two leather squares were hand-sewn together using sinew and nettle strings. The seam was coated with an adhesive admixture, which covered the sinew/nettle thread and sealed the pierced holes. While ethnographic accounts refer to strings dipped in pitch before being sewn (see Appendix 3), here the seam was coated and not the string, as a coated string would be less flexible and manageable. The product was left to dry for seven days (as in Baker et al., 2021). The experiment investigated which material combination better maintains the structural integrity of the seam after being immersed in water for 48 hours (pre-testing showed that less than 48 hours did not have an immediate effect on a shear test, and more than 48 hours rendered all samples too unstable). The test was conducted by applying a force pulling the sewn leather squares apart and observing their reaction. The experiment tested the reaction to a pulling force of a total of 10 leather samples (See Table 3).

Table 3. Sample name with adhesive and string material.

The hypothesis is stated as follows:

1. The control group fails.
2. The coated sinew resists better than the nettle.
3. Some combinations hold better than others (possibly BBT+ additive), but none are completely unaffected by the water.

Preparation:

1. The sinew and nettle strings were created. When dried, hair-thin fibres were manually extracted from both. The fibres were collected in bundles and twined to form resistant strings (See Figures 5, 6) (approximately 5 mm wide and 15 cm long) with an S-and-Z twist (See Figure 7).
2. The deer leather was cut into squares. Two squares were selected for each of the 10 samples. The extremities of each couple of squares were superimposed for approximately 2-3 cm, four holes were pierced through and sewn with sinew and nettle (See Figure 8). The holes were pierced using modern metal implements, for time constraints, however, one hole was created using flint tools to demonstrate that it is achievable (See Figure 9).
3. Birch bark tar was extracted from birch bark with traditional methods from the University of York. 100% pure beeswax and resin have been purchased from online retailers. The three adhesives were heated up on an open fire (See Figure 10). As per Schmidt et al. (2023) results, the tar was maintained on the heat for approximately 90 minutes, with the temperature shifting between 80° and 300° C in an open fire setting. Beeswax and Resin were heated until liquid (5-10 min). Each adhesive combination was applied on its proper leather and string sample with the aid of a stick, quickly reheating the adhesive when hardening (See Figure 11). The samples were left to dry for seven days in a closed environment. Figure 12 illustrates the eight samples with adhesives right after application.

Test

All 10 samples were immersed in water for 48 hours. Following, two pierced rivets were applied to each side of the leather squares (total of four rivets per sample) to protect the leather from ripping during the shear test. One side of the sample was hung from two wires passing through the rivets. On the other side, a weight was hung from two wires passing through the rivets. The weight pulled down the leather squares simulating a shear test. The weight selected was 5 kg, producing a force of 49.05N (W=mg). The weight had been selected through a process of pretesting. The experiment recorded the reaction of the various samples to the pulling force through visual evidence. When the seam was held, the weight was removed after 30 seconds.

Results

Table 4 illustrates the visual results of the experiment and observations.

Image	Observations
	BBT: The adhesive lost mass in the water because it was not completely dried. The seam held the weight.
	BBT: Fails, however it took longer to slip out of the holes than the other sinew failure samples (approximately 10s).
	BBT+BW: Fails. It is suspected a fault in the processing of the adhesives, leather piercing or strings.
	BBT+BW: Fails.
	BBT+PR: Well performing. It maintained the leather squares attached.
	BBT+PR: Well performing. It maintained the leather squares attached.
	BW: While easy to crumble, BW still partially sealed the pierced holes and maintained the string attached to the leather, hence it is more successful than the control group.
	BW: the BW starts to crumble but it was still well adhered to the leather and the seam, hance kept the squares well attached.
	Control: The nettle partially held the leather squares together.
	Control: The sinew slipped out immediately.

Table 4. Photographs of the experiment and visual observations.

Sinew was overall less successful than nettle in water because it became porous and absorbent (countering hypothesis 2.). Here, it is noted that BBT+PR and BW were the only combinations completely dried after seven days. The other adhesives were still tacky and viscous on the seam. Hence, the drying conditions might be important for the success of the strategy. Table 5 assigns a value to the success rate of the combinations (Graph 1 in graphic form). There is a difference between BW and BBT+PR in terms of bond stability. BW rendered the seam stiff and was more prone to mass loss, as the hardened nature of the adhesive rendered it easy to peel off from an adhering surface. BBT+PR, instead, retained its mass and rendered the seam much more flexible. Details of the time employed for the activities carried out during the experiments are in Appendix 3. However, the author recognises that time is relatively indicative of an activity because it reflects the skilfulness and knowledge of the maker. The limits of this author's skills and experience in conducting these activities are acknowledged.

Table 5. Assigned value in relation to success rate. 1 = combination that holds, the comparison is nettle control group. 2 = holds well, better than nettle control group. 0 = do not hold, the string slipped out of the holes in less than 5s. 0.5 = do not hold but take a longer time to fail (~10s). +0.5 is added to distinguish the most successful adhesives that hold well the seam.

Graph 1. Graphic of the assigned value in relation to adhesives' success and to string's success.

This experiment encountered some limitations. The failure of the BBT+BW for both sinew and nettle might have resulted from a mistake in the admixture's heating and application, alternatively, it might have resulted from thinner strings or larger holes. Even though treated as constant, handmade strings, leather holes, and drying conditions might have resulted in variable aspects given the actualistic nature of the experiment. The 5 kg weight to test the samples' resistance has been maintained stable for each sample to obtain a constant. An actual shear test calculating the force necessary to break the seam could have been a feasible strategy, however, it would have added variables to the experiment. The experiment has purposefully not tied the strings at the extremities of the leather squares, allowing the string to slip out of the hole. If done otherwise, it would have been difficult to methodically determine if the seam was held by the adhesive or by the string knot.

Discussion

Firstly, the experiment demonstrated that it is possible to devise a waterproofing strategy for complex clothing. According to Graph 1, certain combinations, for both sinew and nettle, were better performing than those with no adhesive (control sample), hence confirming hypothesis 1. Secondly, the results have highlighted the combinations' success rate, revealing that some performed better than others. BBT+PR and BW provided greater structural integrity to the seam after immersion in water (BBT+ PR providing better flexibility to suit body movements). Thirdly, it was noticed that, for better waterproofing performance, it is essential for the adhesive to dry completely on the adhering surface.

Discussions about the strategies used in Neanderthals' occupation of Eurasia can spark speculations about behaviours and environmental adaptations to wet and cold environments. To interpret use, it is important to engage in a conversation about technological complexity, understanding the efforts necessary to build technology.

Oswalt (1976) measures complexity by counting the number of units ('techno units') composing the technology, with more parts rendering it more complex. Perrault et al. (2013) add that not only the number of parts but also the 'procedural units' (the number of steps to manufacture each part) influence the overall complexity. Compound tools attest to a certain level of complexity and ability to conduct multi-level planning. Each part requires an individual process and mastery for manufacture, to be a unit of an interconnected whole. In this interconnectivity, if one element fails, the whole structure does too (Sterenly, 2020). Therefore, the success rate of each component must be exceptional for the whole complex to be reliable.

If the complexity of the strategies employed for this experiment is evaluated and compared with success, some interesting arguments can arise. Looking at the materials selected, aspects such as availability in the territory and ease of collection and manufacture can shed light on the complexity of each part composing the tool. The 'Materials and methods' section has evidenced the wider availability, ease of collection and manufacture of nettle in respect to sinew. Hence, nettle could present a quicker and more reliable component (according to the results). Focusing on adhesives, it is understood that BBT, while its primary source (birch bark) is available and easy to collect, requires a complex and long process for extraction and reduction (24 minutes to 24 hours according to Koch and Schmidt, 2023; 1.5 hours for heating reduction on an open fire at high temperatures during this experiment). PR, on the other hand, as noted in 'Materials and Methods', is similarly available to BBT (as pine and birch belong to the same biome) and quite easy to extract - collected from wounds in trees and branches (Kozowyk and Poulis, 2019; De Freitas et al., 2023). It also resulted quick to melt on an open fire (≈5/10 minutes). BW, while available but to a lesser degree to BBT and PR, was understood to possibly retain a level of risk in collecting (climbing trees, risk of bee stings) and some complexity in extraction - filtering honey to obtain the honeycomb material. However, it is likely the byproduct of honey collection and it resulted extremely easy to melt and reheat throughout the experiment. Based on these observations, BBT + PR requires the most effort as it involves the collection and association of two different components, with their relative complexities in acquiring and manufacturing. BBT + BW is excluded from the evaluation as its success was uncertain during the experiment.

BBT+PR presents the highest success rate and the highest cost value. Hence, the main result that can be extracted from this experiment is that successfully waterproofing a seam implies a great amount of effort, as a minimum of three, or even four, separate technological units are required - fibre, leather, adhesive, plus possible admixture. A successful waterproofing technology implies the mastery of all technological units, which demonstrate a level of technological sophistication in themselves. At this point, relating these observations to Neanderthals' evidence, this research asks: what are the conditions that can generate enough effort to successfully occupy wet and cold environments?

Complex systems theory sustains that interconnectedness and population size are directly proportionate to complexity (Kauffman, 2000; Bentley and Mashner, 2003; Kholer, 2012). Muthukrishna et al. (2013) notes that increases in group numbers can lead to greater technological diversity and sophistication. Smaller and more isolated groups are more likely to lose information transmission, hence losing skill sets. This lack of network increases group vulnerability and fragility and diminishes the chances for innovation (Premo and Khun, 2010).

Greater population sizes, instead, increase the need and the possibility for a division of labour, consequently, division of labour allows for the development of more sophisticated and generationally accumulated skillsets (Nakahashi and Feldman, 2014).

Therefore, granted suitable material availability, the prerequisite with which to generate enough efforts to occupy and survive the risks of wet and cold environments are:

• Cognitive: requiring a hierarchical organization of at least three technological units and the consequential capacity for multi-level planning. This capacity is attested in Neanderthals' evidence with adhesive technology which appears from MIS 7 and fibre technology (80 kya).
• Social: successful and reliable strategies, to counter more unfamiliar, fluctuating and unknown environmental circumstances are facilitated by increased group size and geographical interconnectivity, which provide greater chances for job division, technology sophistication and cultural accumulation.

As cognitively able, Neanderthals' social expansion seemed to be limited. Isotopic data of singular teeth and bones, as those found in Lakonis, Greece; Moula Guercy, France and Gruta de Oliveira, Portugal, is employed to sustain a general relevance of individuals' short-distance mobility patterns, in the range of 20 km to 50 km (Richards et al., 2008; Benson et al., 2013; Pike et al., 2016). Moreover, genetic evidence indicates that, in Neanderthal groups throughout Eurasia, high levels of interbreeding generated low diversity rates (Melchionna et al., 2018). It follows that communities were isolated in the territory, delineating patches with low levels of interconnectivity (Castellano et al., 2014; Skov et al., 2020). Additionally, shorter distances covered could have been more beneficial for certain groups such as ill and injured, pregnant women, the elderly and small children. The archaeological record suggests that the support for more vulnerable groups, such as the injured and the elderly - who were probably not able to sustain long daily travels - is attested (Spikins, 2019). There is also isotopic evidence that pregnant women would remain in one location for several months, before and after pregnancy (for instance, Isernia La Pineta, Nadale 1, Riparo Broion and Fumane Cave; Lugli et al., 2017; Nava et al., 2020). This evidence would support a local, short-distance activity model, where long-distance connections were limited, and familiar territories and base shelters were probably preferred. This strategy would avoid dangers such as walking in snow for long distances or being caught in rain or blizzards with no familiar shelter around. With a short-distance movement strategy, a waterproofing solution that can be moderately successful but easily re-adjustable, such as beeswax could be feasible. With long-distance travel, a more successful strategy that does not fail throughout the journey might be more recommended, such as the more costly birch bark tar and pine resin.

These evidence and observations reveal a possible snapshot of Neanderthals as isolated in the territory, hence their development of cumulative culture and more sophisticated, but successful, technologies might have been limited by this factor. For this reason, technological sophistication might have been insufficient to sustain a greater territorial extension. It might have limited their survival in unfamiliar and unknown territories through long-distance travels, presenting the risks of wet and cold environments. In other words, there is a simultaneous presence of causation and consequence: the lack of interconnectivity and limited group sizes would have hindered the achievement of a successful waterproofing strategy contrasting the dangers of wet and cold environments; simultaneously, these dangers would have limited groups migrations and long-distance travels, hence limiting interconnectivity and the possibility for greater success in technological components.

Limitations

The discussions and considerations developed in this research are limited by the hypothetical nature of the experiment. The strategies developed are not the result of direct evidence but a proposition of how a waterproofing strategy, if employed, might have appeared. Therefore, the results and conclusions obtained are hypothetical in nature. The scarce evidence of adhesives and fibre technology constrains the discussion about waterproofing strategies in a limited chronological range (adhesives being around from MIS 7 and the single plant fibre evidence only from MIS 3). Hence, it could be argued that this research's conclusions only apply to occupations of a much-restricted range than that explored in the introduction. However, the scope of this research is to provide one technological possibility and investigate its implications for behaviours and environmental adaptations. The wider context that has been presented provides a broader picture of hominins' occupation of, and adaptations to, wet and cold environments in Eurasia. It is acknowledged that climate fluctuates, periods are dryer and warmer, and technology is not chronologically linear. This research's conclusions do not presume to be relevant for all Eurasian occupations. They provide one possible framework to investigate and understand the relationship between the risks of wet and cold environments and behaviours.

Conclusion

This research has devised a possible fitted clothing waterproofing solution, utilising ethnographic comparisons and Neanderthals' known technological repertoire, that might have protected individuals from the risks encountered in wet and cold environments. It has been discussed that the better-performing material combination requires a high level of technological complexity, as expected for compound tools. Following, the discussion investigated whether the effort analyses can shed light on the challenges that wet and cold climates may have imposed on Neanderthals and the limitations they might have possessed to counter wet and cold conditions. While cognitively able, as evidenced by archaeological findings, Neanderthals may have been constrained by social dynamics, as geographic isolation likely limited their group sizes, exchanges, and networks within their territory. Here is proposed that ecology and behaviours are co-constituted. A social limitation would restrict the development of complex waterproofing strategies, hence wet and cold environments would limit Neanderthals' territorial expansion. Simultaneously, the dangers of wet and cold environments, as met only with great efforts, would restrict territorial expansion, hence the social network.

This research has added relevant information on the technological performance of organic, perishable materials - leather, fibre technology and natural adhesives. These are highly understudied, as they are rarely preserved in the Palaeolithic archaeological record. This research has aimed to spark an interest in a more focused understanding of environmental adaptations. It has investigated Neanderthals' cold adaptations through a narrower perspective that centred on the risks and potential solutions for cold and wet environments. Moreover, it has proposed a discussion that unravels the tangled relationships between environments, behaviours and technology, finding mutual causation and consequentiality between them. Future research could devise countless other experimental methodologies testing: other adhesives, strings' strength, other fitted clothing designs, the point of breakage through a proper shear test rather than a fixed weight and testing other possible waterproofing strategies (e.g. water resistance qualities of different furs/vegetable clothing sources). Moreover, future research could, through a GIS investigation, determine if there is a visible avoidance, in various chronological timeframes, of wet environments or not, which could suggest successful adaptations. Finally, an attention to waterproofing could be expanded not only to clothing but also to containers, to understand how liquids might have been stored and transported. This particular interest could then initiate investigations into adaptations to particularly arid and hot environments instead. In conclusion, this research has proposed a methodology that optimizes the use of experimental strategies, even when hypothetical, and it has investigated environmental limits through a wider lens, recognising complex and ambiguous dynamics that affect, and are affected by, hominins.

Acknowledgements 

This research is the result of my MSc dissertation at the University of York. I want to thank my supervisor, Professor Penny Spikins, for her availability and guidance through this research, Professor Andy Needham and Professor Gareth Perry for providing me with the material and information to conduct my experiment at the YEAR centre in the University of York.