Where did the Neanderthals go?

The disappearance of our closest relative, Homo neanderthalensis, is a mystery that will surely haunt scientific and popular literate for as long as the written words exists. The simple fact that we are the single survivors of a line of large-brained apes begs the question, where did they go? The most parsimonious explanation in the case of Homo sapiens versus Homo neanderthalensis is that the former outcompeted the latter. Competition is defined as an interaction between species that results in the fitness of one species being affected by the presence of another. This can be direct competition for resources, or indirect competition within a similar environment (Kersting et al., 2005). Many researchers cite the disparity between cultural capabilities seen in the two species. This is evidenced by a significant increase in cultural complexity and therefore cognitive function. This would have given Homo sapiens the edge they needed to displace Neandertals from their base in Europe. Before establishing which avenue the competition between these two species occurred in, a case for overlap must be made. The most frequently cited evidence for this type of competition is to be found in the Levant, and in France and the Iberian Peninsula.

The time frame in which this overlap occurred began as early as 135,000 to 100,000 years ago in the Near East Levantine corridor (Joris and Street, 2008). In this narrow corridor couched between the mountains and Mediterranean Sea, the population of the two species could never have been very large, perhaps reaching no more than 10,000 (Shea, 2003). In this area, two species with similar metabolic requirements would be in direct competition with one another if they lived in similar temporally and geographical locales (Shea, 2003). Many researchers have speculated on what this type of overlap would mean with such closely related species. Both species appear to have relied heavily on large animals during the Middle Paleolithic (Shea, 2003). Early modern humans disappear from the Levant between 130,000 and 80,000 years ago, supposedly being replaced by Neandertal populations who themselves disappear for the last time 50,000 to 45,000 years ago (Shea, 2003). This pattern could be the result of competitive displacement by each of the species as climates or technologies shifted in their favor. Some researchers point to the lack of cultural sophistication of early anatomically modern humans as the reason for this pattern, citing a heat adapted species literally being unable to expand beyond the territories of a cold adapted cousin. Many researchers agree that the cultural complexity of the two species was very similar prior to the time of AMH dispersing into Europe, but the time thereafter is hotly debated.

Despite the temporal proximity of the two species in the Levant, the real evidence for an increasing cultural gulf is to be found in Europe. Due to dating advances centered on the removal of “young” contaminates in bone and other cultural material made at Oxford University, it is now possible to tighten up the time-frame in which Homo sapiens moved into Europe, replacing the Neandertals. If this dating technique bears out, the shift from one species to the next occurred between 46,000 to 41,000 yr BP via calibrated carbon dates, a span of 5,000 years (Mellars, 2008). Indeed, even generous dates show that Neandertal fossils are found only before 38,000, while AMH are not dated to before 35,000 (Joris and Street, 2008). Because of this we look to cultural material characterized by the Aurignacian to determine the presence of one species over the other. In Southwestern France and the Iberian we have the greatest cause to believe there was contact due to the overlap of cultural materials (Mellars, 2006). The evidence here does not support a long coexistence of Neandertals and AMH (Mellars, 2006). In reality the cultural differences during the contact of the two species is void of substantial behavioral and cultural difference. Their subsistence strategies, lithics capability, burials, and ornamentations were nearly equal. It was not until after Neandertals had already disappeared that cultural complexity in Homo sapiens can be firmly established (Carnieri, 2004). Although this view is highly controversial, we could bear it in mind as we look towards other reasons for displacement.

The overall case for Neandertals being outcompeted is articulated by Richard Klein, who argues persuasively that behavioral modernity was the result of a brain mutation that allowed for Homo sapiens to view the world in a different way (D’Errico, 2003). The alternative sees the trajectory of complexity have deep temporal roots which are found in Africa some 250,000 years ago (D’Errico, 2003). Both scenarios reach fruition some 40,000 years ago with the second dispersal of AMH from Africa into Asia and Europe. The later of the two hypotheses explains the clear cultural complexity as a result of population density and basic subsistence needs acting upon the early human societies. An analogy is draw between Pleistocene Aboriginal Australians and Aurignacian people, which points out identical cognitive abilities that possessed different material culture and symbolism (Langley, et al. 2008). The argument here is that cultural complexity will manifest should the need arise, not simply because they are able. According to this later progressive model, “biological and behavioral modernity were inextricably linked, advancing together in a long and slow dialectic (d’Errico, 2003).” Evidence for a similar scenario is to be found in “transitional” Neanderthal tool industries that hint at a growing complexity of lithic material, such as the Chatelperronian (d’Errico, 2003).

The largest disparity between the pre-transitional assemblages of the Neanderthal and the industries of AMH is one of flake versus blade. If there was an advantage to be had between the two assemblages it would be found in cutting edge versus tool weight. Some researchers have quantified the gains of one over the other, claiming at most 5 or 10 times for blades over flake (Metin et al, 2008). The testable basis for these claims are that : “(1) blade technology produces more blanks, and thus (2) unit volume of tool-stone is more effectively and completely consumed and, most significantly, (3) vastly greater lengths of cutting edge per unit weight of tool-stone are produced (Metin et al., 2008).” When these claims were tested between the two tool types it was shown that “blades started out with 1.53 times more cutting edge than the flakes and 1.49 times more cutting edge per weight (Metin et al., 2008).” When the flakes and blades were sharpened to exhaustion they “accumulated 1.12 times more cutting edge than the blades and 1.15 more cutting-edge per weight of stone (Metin et al., 2008). Not only did this test disrupt the claims of cutting edge advantage, but it showed that ultimately flakes were a more economic use of such a precious resource. Further, the discoidal reduction was less risky to produce and that for every 100 grams of material consumed 1.22 more blanks than the blade cores were produced by flakes (Metin et al., 2008). Still, Homo sapiens would not have switched from one technology to the other without a reason. This reason can be seen in a shift in subsistence strategy, linked with anatomy.

If we look at the remains of Neanderthal skeletons we see evidence for a “draw near” hunting type which demands that they confront animals from a short distance, thereafter thrusting to kill the animal (Carnieri, 2004). It has been shown that thrusting was a source of strength asymmetry in both species in the Middle and Early Upper Paleolithic (d’Errico, 2003).This method was very dangerous but ultimately successful and was probably aided by the Neandertals well muscled frames. Regardless of this physical advantage, the points fashioned by Neandertals and Homo sapiens soon after this period reflect a difference in hunting types. In terms of aerodynamics, the Homo sapiens points were made to be “thin, straight, and light.” This indicates that Neandertals might have favored heavier weapons for closer hunting, while AMH preferred to throw their weapons. In the cold logic of Evolution, placing yourself in higher danger could reduce your fitness and thereafter allow for a species with a higher fitness ratio to increase their population gradually.

This pattern of subsistence and cultural shifts would only be augmented by a dietary disparity between Homo neanderthalensis and Homo sapiens. A reconstruction of Neanderthal caloric requirements done by Dr. Steven Churchill showed that 4500 to 5040 calories per day were required to maintain the bulk of their bodies (Science 307, 2005). The methods of using the La Ferrassie skeleton, traditionally living Inuit, and silicone to estimate mass surely has its faults, but the illustration is clear: If a modern Inuit can be used as a proxy for an AMH in an environment similar to a Neanderthal, they would require 3000 to 4000 calories per day. For a week the Neanderthal would require 31,500 calories, and a mixed band of 10 would require 315,000 on the low end. The Inuit needing 28,000 calories per week would require 280,000 on the high end for a band of 10. This results in a difference of 35,000 calories per week, which is more than enough calories for another Inuit (Science 307, 2005). Although these calculations are rough, the caloric requirement would be equivalent to one healthy caribou per month (Science 307, 2005). The stress of the lack of food is evident by the Harris lines and other dental indicators on the skeletons of many Neandertals.

When you couple the concept of a more demanding metabolic rate with the fact that meat composed a large portion of the Neanderthal diet, while the AMH diet is understood to be more varied (d’Erricho, 2003, Richards et al, 2008), it only enlarges the gulf between availability of calories to the two species, thus reducing the fitness of Neandertals even more. If one turns this line of thought solely upon the difficulties of remaining alive to reproductive age, it should be noted that recent models addressing the question of Neanderthal brain size show that their larger brains appear to be the result of more rapid growth rates during adolescence ( (de LeÃn, et al. 2008). This in itself would be more calorically demanding for adolescent Neandertals, especially if they required a higher percentage of protein as compared to their “human” cousins. And even when the females reached adult age, it would be harder for them to maintain a healthy enough state to maintain fertility due to stress reducing the frequency of their ovulation cycle (Science 307, 2005). Under such a light it is no wonder that later Neanderthal populations increased the breadth of their dietary resources by concentrating on smaller bodied animals and even moving onto marine resources (Stringer, 2008). Incidentally this later evidence comes from the site of Gibraltar which may have been a refuge population for Neandertals after a climatic event which exacerbated those issues which have already been discussed.

Although some researchers have claimed that Neandertals lacked the ability to adapt to “when the herds gave way to more thinly spread steppe animals and migrating groups that had to be followed (Holden, 2004).” It appears that a climatic event around 39,000 years ago occurred. This event, called the Heinreich 4, features a series of icebergs sliding into the North Atlantic and reducing sea and land temperatures around Europe (Mellars, 2006). This led to the deforestation and rise of desert like conditions in the Iberian Peninsula and Southern Europe (Joris and Street, 2008). The H4 coincides with the time-frame for the disappearance of the bulk of Neanderthal populations between 41,000 to 32,000 BP (Oxford “Ultrafiltration” calibrated dates) (Sepulchre, et al., 2007). This is the time which we see the Aurignacian culture dispersing into the North of the Iberian between 42,000 and 41,000 BP (Sepulchre et al., 2007). The argument being that this climatic event actually separated the two species is evidenced by Aurignacian cultural material appearing in the Southwest around 35,200 BP (Sepulchre et al., 2007). The refuge populations of the Neandertals could have been a result of climatic pressures coupled with an encroaching species. In fact it seems that the patterns of encroachment by AMH closely followed climatic events such as the improvement of conditions between 43,000–41,000 years ago (Mellars, 2006). Considering this it would seem appropriate that a harsh climate allowed the Neandertals to adjust their diet in order to compete more readily with the new threat. This is shown to be the case with evidence of exploitation of mollusks, fish, birds, and dolphins at Vanguard Cave, at Gibraltar and Moscerini Cave in Italy (Carnieri, 2004). In fact Gibraltar may have been one of the last refuge populations of Neandertals. Studies done in this area seem to buttress the idea that “Upper Paleolithic human levels of occupation in Gorham’s show behavior similar to that of Neandertals and similarly complex subsistence strategies that allowed them to exploit marine resources (Stringer et al., 2008).”

In essence what we are really discussing when we are talking about strategies such as these are the Neandertals’ ability to construct and maintain a niche that allows them to remain alive. Homo sapiens ability to construct a niche that a population can flourish in is also a central question to the topic of Neandertals disappearance. The concept of niche construction is used to frame this argument. Competition in this sense is when “a species ‘effects’ changes in the environment to which another species must ‘respond’ (Vandermeer, 2008).” If a species is dependent upon a population’s ability to gather food in groups, construct or maintain a shelter, gather fire-wood sufficient to remain warm during a climate shift, or simply address the needs of a pregnant mother, it goes without saying that this is requisite for survival. Both Homo sapiens and Homo neanderthalensis were species that lived in bands which depended upon one another for survival. Should a band not have enough adult members to provide food for its dependants, the population must be reduced in order for other members to survive. The number of members required to maintain and construct a niche is inextricable linked to the amount of members that can be a part of the band. This concept is the dynamic of necessary and sustainable population (Vandermeer, 2008). This line of logic shows that a certain saturation will occur if a population grows to large in relation to its resources, not unlike the claim of Thomas Malthus. Similarly, should a population fall below that required to maintain a niche it will be forced into extinction or a lower level of niche production (Vandermeer, 2008). It is self evident that a pair of species with similar abilities and requirements would be in a precarious situation should both be pushed to a limit during a climatic shift. Something as narrow as the amount of calories required to maintain personal and reproductive health, the breadth of dietary sources, and the potential to support a higher population because of these facts, could make all the difference.

It is from this vantage that we can address the level of cultural complexity evident in the AMH versus the Neandertal record at the beginning of the paper. It has been proposed that an increase in regional concentrations of AMH was a catalyst for cultural complexity (McBearty and Brooks 2000, d’Errico 2003, Habgood, 2008, and Slimak, 2008, Shipman, 2008). This backdrop of population and cultural progression can be seen in a model developed by Borenstein et al., to explain cultural transmission through social networks. The keys to this model in relation to our question is that “…niche construction may generate selection pressures that lead to fixation of otherwise deleterious alleles, maintain genetic polymorphism where none is expected, eliminate what would otherwise be stable polymorphism, and produce time lags in the response to selection, as well as other unusual evolutionary dynamics (Borenstein, et al., 2006).” If we use this relation of networks, population size, and cultural innovation we can seem to flesh out an explanation for the symbolic behaviors used to gauge Klein’s modernity or cultural complexity. “Social networks, the vehicle of cultural evolution, are not static, but rather change over time, often owing to the evolutionary dynamics of other coevolving cultural traits (Borenstein, et al., 2006).” It should be noted that comparisons of cognitive expressions could be misguided due to the fact that AMH occupied multiple continents by 45,000 years bp (Langley, et al. 2008). This would provide a greater potential for social networks to develop, and cultural innovation which could more easily percolate. It goes without saying that the population size after the H4 is clearly in the favor of Homo sapiens even if the networks were not very large.

Competition between Homo sapiens and Homo neanderthalensis is a series of complex events. The largest discrepancy is clearly shown by the cultural innovations of the two groups. Klein captured the question when he said: “the essential issue is cause and effect: whether population growth drove human behavioral change or behavioral change drove population growth (Habgood and Franklin, 2008).” The obvious implication is that cognitive differences led to being outcompeted. The list created to measure this excludes many contemporaneous and modern populations (Langley, et al. 2008). Indeed Australian Aborigines had little or no blade production until recent times (d’Errico, 2003). Furthermore, blade technologies do not appear to have intrinsic competitive value in regards to cutting ability as shown by Mertin et al. If we bring the concept of cultural complexity to the fore, we can mark an exponential increase in frequency through time at 20,000 year intervals starting at 150,000 years BP (Langley, et al. 2008). This would mark an independent incline of complexity that is no more “an ‘impossible coincidence’ than the multiple independent origins of agriculture (Langley, et al. 2008).” It is evident by ‘transitional’ assemblages that this incline was disrupted by events that are still unclear, (Slimak, 2008) but it may indicate that the last Neandertals could have been contemporaries early AMH (Joris and Street, 2008). Knowing this there does not seem to be a reason to invoke a cultural revolution to explain the disappearance of Neandertals.

To conclude, if Neandertals biological requirements were simply higher, their biology more inclined to a dangerous hunting style, and climatic events characterized by the H4 led to a bottleneck, it would seem evident that their fitness would be drastically reduced. Thereafter the Neanderthal population would be grossly inadequate when compared to anatomically modern Homo sapiens, and their pattern of cultural innovation would no longer be tenable. If we apply niche construction as a frame, we can see that a population can only be sustained if a certain amount of individuals are contributing to the procurement of sustenance and shelter. From here their reproduction would be directly impacted and the Neandertals would be unable to maintain the populations they once enjoyed. The reduced late refuge populations that exploited a greater variety of resources would not be enough to generate the cultural innovations nor the networks required to directly compete with the ever increasing AMH populations and, in the end, a series of events reduced the Neanderthal populations until extinction was assured. If the logic of this scenario holds, it would appear plausible that Homo sapiens outcompeted their cousins Homo neanderthalensis, not by a cognitive revolution, but by biological and climatic serendipity.

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The Course of Evolution?

Human evolution in the future will surely be an interesting experience. When handling such a question it is important that we are not Americentric. Because evolution takes place more prominently in centers of strong selection pressure, we must look towards this pattern for our answer. This does not exclude relatively stable western environments from the course of evolution, but it does make the projection less obvious. This becomes a question of dichotomous nature: Evolution acting upon those who are surrounded by security and resources, and those that are surrounded by a harsh environment filled with deleterious elements. In regards to this medicine is an especially striking issue. In less developed countries, pathogens and nutrition concerns are sometimes at a greater lack than in the evolutionary environment. In contrast to this modern medicine in developed countries allows people to reproduce that may not have within our evolutionary environment. Both issues are a direct result of the agricultural, industrial, and medical revolutions. Human biology is impacted by these advances in different ways but in reality the longevity beyond reproductive viability observed in developed nations has nothing to do with evolution. Medicine only impacts the population when it allows people to reproduce longer than they would have without it.  

The true crux comes down to mating strategies that are related to current environments. To stretch a poetic analogy over the evolutionary framework we can turn to Alfred Tennyson’s Ulysses. Although he surely did not mean to, he placed the pathways of our evolutionary course into the opening lines: “It little profits that an idle king; By this still hearth, among these barren crags, matched with an aged wife I mete and dole; Unequal laws unto a savage race; That hoard, and sleep, and feed, and known not me (Beaty et al. 2002).” Had Tennyson added the vulgar term rut to his list of barbaric actions, he might have had it all. When we consider the question of human evolution in the future we simply must find out what reproductive strategy is most successful at the moment. Tennyson answers this question in his own way. Ulysses, being a traveling hero, also says “I am part of all that I have met.” This would be the case with a in that he surely would leave behind many illegitimate children. To analogize further, traveling military men and modern businessmen are not exactly known for their fidelity. Alan Miller and Satoshi Kanazawa point out that our minds really function on a primitive scale. We are moved by those biological behaviors which were successful then. Women are attracted to mates of quality, and cuckholdry is always an option.  This was certainly the case then, before the modern advent of birth control, and is much the case now. This only highlights one portion of the poem; the savage race that Ulysses complained about surely has a place within evolution.  

Most people consider those of impoverished conditions to be the sector of the public prone to breeding uncontrollably. One must only look at the current western media for anecdotal support. Those portions of the population get heavy airtime on reality shows and talk shows like Jerry Springer. This is largely a fabrication of the media. In reality we must take into account that those with resources enough will be able to raise their children to reproductive age. Those without enough resources will not be able to. This is the level that evolution acts upon. Those that are truly in dire economic straits, such as Sub-Saharan Africa, have a total fertility rate that exceeds 6 live births within a woman’s reproductive years. In the United States the fertility rate sits a little above 2 (Rubenstein, 2008). Those that live to reproductive age in the environments to which they are born have their own suite of environmental pressures to deal with. In Sub-Saharan Africa their selection pressures result in an infant mortality rate ten times that of North America. It is not difficult to find a place for access to medicine at the center of this contrast.  

Medicine has been an influence to our species since its discovery. The ability to control the course of pathogens, prevent death, and improve overall health has helped bring about a population of titanic proportions. This is in line with the population increase observed after the agricultural and industrial revolutions. With an increased population comes an increase in the ability to sustain and promote greater genetic variation.  There are now genes being exchanged which would be considered “bad” in the evolutionary environment. Examples would be genes that render a person partially limbless or blood conditions like hemophilia. As Dr. Moalem points out, there are also genes that were potentially “good”, such as diabetes, but are now “bad” in our current environment. These genes have been allowed to persist because medicine can make them annoyances instead of fatal. Many people point to the idea that our gene pool is becoming diluted or even polluted by allowing such conditions to persist. This line of thought is certainly related to the eugenics movement of the early 20^th century, and is just as fallacious.  

Many medical innovations on the horizon are currently aimed at eliminating such issues through gene therapy. This is not the course of our evolutionary future. Fischer’s fundamental theorem of natural selection sees the genetic homogeneity of this goal as a bad thing. This is because we are never sure what the environment of our future will be like. If someone with hemophilia also has the ability to stave off a super-virus or deal with rapidly changing environments tied to global warming, all the better. An increase in variation directly correlates to the health of the species. It follows that medicine should maintain the course of promoting or augmenting the health of an organism without damaging its ability to produce variation. This would be the course that provides an evolutionary future. It would seem the cultural trend of humans is that they become more tolerant of differences as they become more cosmopolitan. Therefore a shift from traditional aspects of variation would likely be the line of the next revolution. Not outside this concept is the shift from personal extension through prosthetics from trope to form.  

Prosthetics, once used to replace limbs, has found a new niche within technological culture. Although a fringe now, prosthetic extension is experimented with by those with no condition that would demand such objects. Medicine has made available an ability to augment natural ability through advances in this customized line of treatment. Although this is at the moment something entirely external, there are movements towards biological incorporation (Smith and Morra, 2006). In the field of study concerned with nanotechnology, interest in internalizing power supplies via modified eel electrocytes has produced significant results (Xu and Lavan, 2008). This method of energy production would work directly through the metabolic system, and could be used to power machines thereafter. With very little imagination one can instantly see the medical leaps we could make if only we could power the cumbersome mechanisms we have invented to handle heart conditions, breathing issues, and digital pain suppressors (Albert et. al. 2006). This incorporation of borrowed cells into our own bodies to augment ourselves would become a biological reality that could have implications on the scale of modern evolution.  

This projection only becomes clear if we synthesize select patterns present in the more developed countries. High obesity rates, the desire for symbolic internal and external modification, the presence of a technocentric elite, and the new ability to internally power digital apparatus, we might see the culmination of the computer age. People who were once obese would now have the extra calories needed to power their internal devices via electrocytes within the body. This ability could render the individuals willing to engage in this path more influential. If the behavior that allows for the decision to engage in risk of such an extreme modification is under genetic control as well as the trait of obesity than selection could be present. Of course this would only be true if there was an advantage.  

Indeed, within our current culture there are many of the most recent generation that would leap at the chance to merge with their iPhone. This idea spurs both disgust and fascination. The ability to track your position on the planet via the installed GPS makes you more punctual, or constant access to newsfeeds makes you more efficient in the office, cultural selection would be present. To push the concept further, advances could one day reach the level of direct cognitive enhancement which would certainly give an edge analogous to a beneficial mutation. Furthermore, real-time health monitor into this system would increase lifespan and possibly alert people to emergency conditions before they occur. This, much like previously mentioned revolutions would help to increase genetic variation within the species.  

The benefits of such innovations are clear from a medical standpoint. Access to such innovations would radiate from the center like the industrial revolution from London and the agricultural revolution form its multiple centers. Clines could form around people with the biology to support such a system, much like lactose persistence or G6PD. Those with access to the example synthesized here will surely be the Ulysses of their age. The professionals could that afford the higher priced modifications would have greater access to the resources that resonate at the level of sexual selection. This would lead to an ability to reproduce and sustain those offspring. Those left behind would be no different than those infants dying in areas like Sub-Saharan Africa because they simply lack the resources to access the two more recent revolutions that more developed nations have experienced. At a fundamental level all environments revolve around our Paleolithic brains. And just like these prior revolutions, the allelic fingerprints of the coming revolution will not diffuse across the entirety of the species equally. It will simply spread into the environments where the behavior is available and beneficial. However this course works out, it is surely occurring on a macroscopic level. In some ways we have are placing a toe into new evolutionary waters while the bulk of population remains in other evolutionary settings. Fischer reminds us that any extension of variation, even those that fail, is an aspect of evolution that is not a weakness but a strength.