Afterword: The Aegean Nexus for Hominin Dispersals in the Middle Pleistocene

The Aegean basin today is a crossroads for refugees, asylum seekers, and immigrants traversing the region by land and by sea seeking a gateway to Europe for safety and better lives. The streams of humanity follow paths over land and sea that have been explored by our ancestors for upwards of a million years. This is an important and timeless topic. It is no surprise then that the articles in this special issue of JEMAHS cluster around questions of human dispersals and adaptations during the Pleistocene and early Holocene. Evidence is rapidly accumulating that multiple waves of humans, including perhaps archaic forms like Neanderthals, followed terrestrial and maritime routes through the Aegean basin. When viewed from the perspective of this small but strategically positioned region at the juncture of three continental landmasses, a picture is emerging of complex and multifarious hominin migrations through time.The idea of the Aegean as a nexus of hominin migrations—as opposed to being a cul-de-sac separate from the mainstream of important events in the Paleolithic and the Mesolithic—has developed considerably since the first conference on the subject held in Ioannina, Greece, in 1994 (Bailey et al. 1999). In the ensuing thirty years new fossil and archaeological evidence for early humans from the mainland and the Aegean islands has been richly augmented by a spate of new finds of fossils and artifacts brought to light by field survey and excavation. And new fields of study, especially those based on the natural sciences, are contributing to interdisciplinary research to unravel the varied processes of change that helped drive the actions of early humans through a dynamic process of feedback loops that characterize the co-evolution of human settlement and landscape change in the Paleolithic and Mesolithic periods.The articles in this issue are based on papers presented at the conference “The Palaeolithic and Mesolithic in Greece and the Eastern Mediterranean: Data and Debates,” held at the University of Manchester in June 2023. We are learning that hominins were present on the mainland of Greece and Turkey early in the Middle Pleistocene ca. 900,000–700,000 years ago (Tsakanikou et al., this issue) and were making open-sea crossings to the Aegean islands as early as 233,000–217,000 years ago (Carter et al., this issue; and Taffin et al. 2024). The hominin species that first explored and later occupied the mainland and the islands are a matter of debate, but they all experienced a different world in the Pleistocene. At times glaciers covered the high sierra of the mainland, and the sea lay far from its present shoreline. There were straight-tusked elephants, hippos, rhinos, bears, hyenas, and lions that roamed sagebrush steppes and open park-like plains, and pygmy mammoths, hippos, and deer grazed in herds on the larger islands in the Aegean. At other times the glaciers retreated, forests expanded, and sea levels approached modern levels. The evidence for this picture—almost of another planet—has long been available, yet some people may have a difficult time visualizing it because the Mediterranean landscape today is shaped and maintained primarily by human action rather than by global climate and biotic communities.To know what the Pleistocene landscape was like when hominins make their first appearance we need a better chronology in order to correlate archaeological evidence with environmental reconstructions. This is difficult to do because the global climate in the Pleistocene was unstable compared to the Holocene, a fact that requires a detailed archaeological chronology, which is currently unavailable for most of the Pleistocene. The problem can be illustrated with an example. One period of the Pleistocene from 60,000 to 30,000 years ago (Marine Isotope Stage 3) was a time when both Neanderthals and early anatomically modern humans were present in the Aegean. They had to adapt to at least 15 oscillations of climate from cold stadials to warmer interstadials in rapid succession. These oscillations lasted from a few decades to a century or two, and the transitions (Dansgaard–Oeschger events) could be rapid. Climate instability has obvious implications for archaeological interpretations. Humans had to adapt to extremes of climate that were constantly evolving. Warmer conditions in the interstadials required them to expand their home ranges as forests spread across the landscape, coastal plains shrank, and islands that had been close to the mainland were cut off by growing expanses of the sea. Smaller woodland fauna became the preferred prey for the hunters in these periods. And when cold stadials returned, people had to adjust as forests retreated, coastal plains reemerged with mosaic wetlands attractive to larger herbivores and their predators, and the islands once again seemed nearer. The periods of glacial cold may also have blocked the northward movements of hominins or forced some to retreat to southern refugia. Despite the obvious fact that humans were obliged to constantly adjust their behavior in the face of these climatic oscillations, we are unable to correlate precisely the presence or absence of any hominin species with specific stadial/interstadial cycles, even in this one relatively short 30,000-year period because of the lack of a precise chronology for archaeological sites. The difficulty of correlating global climate conditions and hominin responses is unfortunate because glacial/interglacial cycles have a bearing on our understanding of the timing and frequency of dispersal events in the Aegean. Did dispersals take place chiefly in stadials when water barriers were less formidable, or in interstadials when warmer conditions made temperate regions more attractive for foraging hominins?Despite these uncertainties, terrestrial pathways across the Sinai and the Arabian peninsula that ran through southwestern Asia and Turkey have been for many scholars the likeliest avenues for peopling the Aegean basin and ultimately the rest of Europe. But the shortest direct route from Africa to the Aegean is only some 300 kilometers across the Mediterranean Sea from Libya to southern Crete, inducing some scholars to consider the possibility that sea crossings may also have occurred, especially during stadials when maritime pathways were shortest. Interstadial terrestrial routes may have followed now-submerged land bridges, and a mix of terrestrial and maritime pathways is possible. But a preference for terrestrial dispersal routes is understandable because archaeologists have long assumed that crossing the Mediterranean was unmanageable for early hominins who lacked the cognitive and technological abilities necessary to construct seaworthy boats and navigate the Mediterranean. It was axiomatic that the Mediterranean was a barrier to migration. Of course, land routes present distinct challenges of their own. For example, the land route that crossed the Sinai Desert and followed the rift valley of the Jordan River into southwestern Asia and ultimately to Turkey, Greece, and Europe required hominins to traverse land bridges (near Port Said), cross the Red Sea at the Bab el-Mandeb narrows, and overcome many other bottlenecks and potential barriers from mountain ranges and deserts to the Bosphorus Strait at the crossing point from Asia to Europe. Humans may also have followed an even longer route running northeast through Georgia and the Caucasus, winding northwestward around the Black Sea before heading into Europe. Still another terrestrial prospect (Tsakanikou et al., this issue) was to avoid the longest routes by traversing the Aegean from Turkey to the Greek coast at times when there were resource-rich terrestrial routes crossing the Aegean during stadial sea lowstands. For all terrestrial routes immense distances had to be covered and environmental barriers such as rivers and mountains circumvented. If we assume that the direct terrestrial route to the Aegean from, say, the Horn of Africa was some 2,400 kilometers of difficult terrain, sea crossings on the order of 200–300 km to get across the Mediterranean to the Greek islands may have been options despite the logistical difficulties of open-sea navigation (Howitt-Marshall and Runnels 2016). Today’s flood of humanity across the Mediterranean demonstrates that Mediterranean crossings are possible, even under the most dangerous of circumstances. Despite the difficulties of both terrestrial and sea crossings, we know that they were overcome, repeatedly, in a complex web of opportunities presented by the constantly changing global conditions and the evolution of human behavior.What were the motivations of migrants in the Pleistocene? Much can be learned through the close study of residential sites, stone tool preferences, prey species, and the distribution of sites and artifacts through space and time, with judicious addition of assumptions about behavior based on the study of neurocognitive patterns in the evolving human brain (Runnels and Holcomb 2024). Inferences are possible about the how, when, and why of hominin dispersals that can be used to build hypotheses for future testing. For example, two patterns of human behavior have been proposed, one called behavioral modernity, which posits that Homo sapiens uniquely exhibits a complex of skills, including the use of symbols, art, mortuary ritual, specialized big game hunting, along with the ability to inhabit challenging environments (like the arctic). The other pattern is described as behavioral variability, which posits that early hominins were capable of using a behavioral repertoire, or “toolkit,” of cultural responses to meet novel environmental situations or stimuli; in other words, there is more than one way to do something (Runnels 2021).Behavioral modernity is linked to characteristics including logistical, technological, and organizational capacities supported by neurological and cognitive structures that enable the calculation of risk and benefit, abstraction, decision-making, and the communication of complex concepts. Behavioral modernity is ascribed by some scholars exclusively to the emergence of anatomically modern humans about 60,000 years ago, and it is suggested that it was behavioral modernity that permitted our species to make more complex uses of the shifting natural environment and undertake risky adventures such as migrations by land and sea. On the basis of the association of behavioral modernity with anatomically modern humans, it is assumed that pre-sapiens hominins, although ancestral to modern humans, did not exhibit the same behavioral and cognitive capacities and were not capable of engaging in complex activities like open-sea crossings. As a consequence of this thinking, it is difficult to understand how archaic pre-sapiens hominins could have engaged in geographical dispersals in the past million years. The fact, however, that earlier dispersal events by hominins are documented to have occurred makes it possible to ascribe behavioral variability to early hominins. Is it possible that pre-sapiens hominins possessed sufficiently broad and flexible technological and cognitive capabilities to vary their behavioral responses to solve new environmental problems by drawing upon a broad set of possible cultural responses?Of equal interest are the precise mechanisms by which hominins carried out their migrations. Here the concepts of behavioral modernity and behavioral variability come into play. Consider the routes that may have been taken by early hominins as they dispersed from Africa to Eurasia. In global terms, migrations to previously uninhabited lands began about two million years ago and ended about one thousand years ago with the Norse colonization of the islands of the North Atlantic (Runnels and Holcomb 2024). The global picture of these events may suggest an interpretation of the Aegean data. We have already seen how the early peopling of Eurasia is thought to have followed terrestrial pathways from Africa through southwestern Asia. For purposes of discussion we can call this the Moses Model: hominins walked out of Africa through the Sinai. Does the Moses Model work for the Aegean, which lies geographically close to Africa? Terrestrial routes required less planning or equipment than maritime ventures, but how much calculation of risk and benefit, abstraction, decision-making, and communication of complex concepts was necessary? The Moses Model does not require the full pattern of behavioral modernity to make these dispersals possible, which may have taken centuries and millennia in the form of a slow creep rather than an organized movement such as that suggested by the word “migration.” Early hominins may have followed prey animals as they moved from one hunting and foraging ground to another, and they drifted from one habitat to another in a process of range expansion. As environments changed, some bands of hominins survived and others became locally extinct. The process was no doubt repeated many times before one or another hominin species became permanently established. But the discovery of Paleolithic stone tools in the Aegean islands (Carter et al., this issue; and Leppard and Cherry, this issue) challenges the Moses Model. Paleolithic archaeological artifacts on islands that were reachable only by sea crossings made by Homo sapiens or perhaps another hominin species lend support to the concept of behavioral variability, assuming that existing cognitive and technological skills were adapted to the novel tasks necessary to solve the problem of how to cross the open sea. Scholars should consider multiple hypotheses: Were there many episodes of sea crossings? Did Paleolithic visitations of the islands lead to resident populations? Were all episodes of island Paleolithic the result of activity by anatomically modern humans or were archaic species also making such crossings?Migratory behavior involves difficulty and danger that threaten the survival of the group. We can assume that hominins, even archaic species, had strong motivations for undertaking risky moves. Unfortunately we cannot use the experiences and motivations of our own species as analogs for understanding archaic hominin behavior, at least not without significant bridging arguments. How can we infer behavior among early hominins if we cannot observe and analyze their behavior? Any attempt to apply our actions in the form of analogies to extinct species of hominins, none of which have ever—or can ever—be observed, is tricky. It is possible that some pre-sapiens hominins, like Homo erectus, shared characteristics with modern humans such as large brains and a dependence on technological culture for survival. Perhaps we can engage in informed speculation about early hominin behavior based on these similarities. If so, hominin dispersals can be seen as part of the ongoing processes of adaptive radiation that take place throughout the biological world where organisms diversify and adapt to new environments (Runnels and Holcomb 2024). Behavior of many terrestrial animals, including humans, can be modeled with mathematical precision provided we know enough about the initial conditions that govern the process. One example is the Wave of Advance model in biology that describes the pattern of the spreading of a species in a new environment (Ammerman and Cavalli-Sforza 1984). The Wave of Advance as used in archaeology is based on principles that assume that the patterns of movement of individual organisms are random within their home ranges as they move out from a starting point to the edge of the range. The random movements result in a definite spreading arc of population movements and do not require agency or planning. As population grows, movement from the center is constant, but as the growth of the population slows and then stops at the center, it continues to grow along the outer edge of the wave. If there is enough information about the physical nature of the environment and the rate of advance, then the shape of the wave can be accurately predicted. There is a problem, though, with applying the Wave of Advance to human migrations. To avoid a complicated digression, it is enough to say that this biological model assumes that the population of an animal species will grow and expand its geographical range in a manner governed by instinctive behavior best modeled as a Monte Carlo random walk. Patterns predicted by the Wave of Advance have relevance for understanding animal behavior, and it is tempting to see hominins behaving like other animals. But there is a difference: human beings have evolved the ability to think, and they use thinking and its instrumentality, culture, for survival. Drawing upon ages of past experience preserved and transmitted to succeeding generations through learned culture, and with the ability to think about the future and to create different pictures of possible outcomes in the mind (and use the stored cultural experience to posit risks), humans can make decisions that are not fully conditioned by their genetic makeup. They have agency. Humans exhibit behavioral agency and may elect to exploit an opportunity, or not to do so (Runnels and Holcomb 2024). This is the essence of behavioral variability, which may dove-tail with the useful concept of affordance. Tsakanikou et al. (this issue) propose the Aegean Affordance Corridor as a model to explore through GIS the specific environmental characteristics that early hominins may have used to make decisions about range expansion, such as soil properties (edaphics) on the island of Lesvos in the Middle Pleistocene. The actors were operating according to a perceived understanding of what the landscape could provide for them in the form of such natural resources, just as rock shelters, springs, and chert sources on Naxos were affordances for hominins in the Middle Paleolithic (Carter et al., this issue).If early hominins had flexible and variable adaptive abilities, this assumption opens the door to the hypothesis that Pleistocene dispersals may have elicited adaptations to changing environmental through the of a range of taken from a and technological If we early hominins the of they have been to agency to those around Perhaps hominins in the Pleistocene Aegean had for making their to what these have This large and as yet hypotheses that be in light of new evidence before they can be but in the of dispersals is to be in the landscape of the human mind rather than in the physical The motivations are to be by the of and it be difficult to them to a few but we can consider a few affordances to island Paleolithic The at on Naxos suggest that hominins were undertaking open-sea crossings in the Middle Pleistocene they were or multiple short On the mainland even the potential hominin population at a few thousand at any is mainland home ranges for hominins in any period were in prey animals, especially if we assume that were not to their way the when larger animals like or There was of geographical on the mainland, including the same affordances of rock shelters, springs, chert and game on the it be necessary or to undertake the of crossing the sea to Naxos or even to when the mainland had Perhaps an from mainland was a perceived that to people to make the years if were the first human to light a on that coast have been to that the no like hyenas, bears, or human were not present to from and danger are not light It could have seemed like consider one The ascribed to the the if by if by as the to the in and of the movements of the in an which the of these for a model of hominin dispersals that to the peopling of the Aegean The Model posits that hominins followed both terrestrial and maritime routes traversing the Aegean a nexus of hominin If this model is for future it questions such Did hominins cross from Africa to the Did they cross from Asia to the Aegean, perhaps Did they cross the Aegean from the coast of Turkey terrestrial routes over the coastal by stadial sea of the from island to island during sea Did they the Aegean basin the route across the through the mainland, and to the Did they from the Were different paths taken by different hominins at different has been learned from survey and of Paleolithic and Mesolithic sites in the that followed the 1994 which a in the rate of the discovery of archaeological and to from the at the conference at the University of there is for about the future of these and questions about the of the Aegean basin.