Pleistocene Water Crossings and Adaptive Flexibility Within the Homo Genus

Abstract

Pleistocene water crossings, long thought to be an innovation of Homo sapiens, may extend beyond our species to encompass Middle and Early Pleistocene Homo. However, it remains unclear how water crossings differed among hominin populations, the extent to which Homo sapiens are uniquely flexible in these adaptive behaviors, and how the tempo and scale of water crossings played out in different regions. I apply the adaptive flexibility hypothesis, derived from cognitive ecology, to model the global data and address these questions. Water-crossing behaviors appear to have emerged among different regional hominin populations in similar ecologies, initially representing nonstrategic range expansion. However, an increasing readiness to form connections with novel environments allowed some H. sapiens populations to eventually push water crossings to new extremes, moving out of sight of land, making return crossings to maintain social ties and build viable founder populations, and dramatically shifting subsistence and lithic provisioning strategies to meet the challenges of variable ecological settings.

Discovering the opposite shore: How did hominins cross sea straits?

“…The extent of the hominin s’ paddling or swimming performance is not known and is the subject of current research [ 75 ]. Even though hominins, such as Homo erectus or Homo floresiensis , possessed the biomechanical requirements for swimming [ 6 ], this appears to be, primarily, a cultural and technical skill [ 6 , 76 , 77 ].…”

“…Whether hominins expanded into Eurasia across sea straits already during Out-of-Africa 1 [ 102 ] is unknown, as there is no direct evidence [ 103 , 104 ]. However, if they did, then they probably crossed one or more of the sea straits in the Mediterranean or the Red Sea [ 59 ], e.g., the Gibraltar Strait, Sicily Strait [ 60 ], and/or the Bab-al-Mandab Strait [ 13 ], or the Aegean Sea [ 6 , 8 , 105 ]. Further major sea straits of relevance are the Strait of Hormuz [ 106 , 107 ] as well as island hopping in Wallacea and the Philippines [ 108 ].…”

“…Many of those expansion phases required the hominins to cross water bodies of varying sizes, from large rivers to sea straits [2][3][4][5]. The extent to which hominins were able to cross sea straits is debated [5][6][7][8][9][10] and agentbased models can hypothetically show how expansions would look like if crossing sea straits are possible. Thus, investigating the factors influencing the success in crossing a water barrier by hominins having no advanced seafaring technology is essential for debating the possible migration routes during the Palaeolithic.…”

Island Colonization and Environmental Sustainability in the Postglacial Mediterranean

“…The negative coefficient for NPP in the best performing model is, consequently, counter-intuitive, considering the importance of this variable elsewhere (44)(45). Other global contexts with evidence for long-term sustainability in HG settlement most often include very large islands, low-latitude islands with very high productivity indices, or both, e.g., [8]. The general exception to this is HG settlement of islands at mid-or high latitudes with high marine productivity; massive marine trophic systems founded either on seasonal plankton blooms or specific conditions (e.g., the Humboldt current; kelp ecologies) support large populations of marine mammals and/or fish occupying apical positions, in turn sustaining human subsistence in very low-productivity terrestrial environments.…”

“…Islands present difficulties for human settlement-not only in terms of the physical challenges that reaching and colonizing them pose, but also because of biotic and physiographic processes peculiar to insular landmasses [1][2][3][4]. Nonetheless, humans have successfully, if differentially, established permanent settlement on many islands around the planet over the last 50,000 years, and possibly earlier [5][6][7][8]. Using the Mediterranean basin as a case study, we seek to understand which, if any, environmental factors have rendered human settlement on islands sustainable over millennial scales.…”