A hypothesis of ape and human evolution based on comparative biology and plate tectonics

What is it about?

There is broad consensus among paleoanthropologists that extant African hominids (Pan and Gorilla) as well as hominins (our direct ancestors or closest relatives following the split from Pan, i.e., chimpanzee and bonobo) originated in Africa. The prevailing view, that hominins became upright bipeds after moving from tropical forests (the current habitat of Pan and Gorilla) to open savannas in East Africa—where they chased large mammals—is contradicted, however, by fossil, paleo-ecological, and comparative biological and physiological evidence. Here, we propose that hominoids (apes), hominids (great apes), and hominins (humans and fossil species more closely related to Homo than to Pan) instead evolved near water and mostly out of Africa. We propose that Miocene (23.03–5.33 Ma) apes had already evolved an upright, tailless body as an adaptation to living in flooded forests, where they engaged in frequent bipedal wading and below-branch vertical climbing—a type of movement we term vertical aquarborealism. This largely Miocene aquarboreal style of locomotion can be seen as evolutionarily intermediate between the above-branch arboreality of Old World monkeys (Cercopithecoidea) and the various belowbranch locomotive styles of extant apes (Hominoidea). Starting from vertical aquarborealism, Homo—at least by the Early Pleistocene (2.58 Ma)—had developed a lifestyle centred around shallow diving, primarily foraging for non-fleeing foods such as shellfish and aquatic plants. We also suggest that the timing of some major tectonic shifts in the African, Arabian, and Eurasian plates during the Miocene, Pliocene, and Pleistocene may help explain key aspects of this evolutionary scenario, including the splitting times of hominoids, hominids, and hominins.

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Why is it important?

This paper presents an integrated alternative framework for ape and human evolution that unifies comparative anatomy, physiology, paleoecology, genetics, paleontology, and plate tectonics into a single evolutionary scenario. Rather than treating these lines of evidence separately, it proposes explicit evolutionary and biogeographic hypotheses that generate testable predictions. Specifically, it argues that (i) the last common ancestor of African apes and humans evolved largely outside Africa, (ii) australopiths are more closely related to the African ape lineages than to Homo, (iii) orthogrady and early bipedality originated in wet forest environments through wading and vertical climbing rather than on open savannas, (iv) the distinctive anatomy and physiology of the genus Homo are best explained by a prolonged littoral phase involving frequent wading, swimming, and shallow-water diving, i.e. the coastal hypothesis, and (v) major tectonic events—including the closure of the Mesopotamian Seaway and the Zanclean Megaflood—played a central role in shaping ape and human dispersal and diversification. By integrating evidence that is usually discussed in isolation, the paper challenges several long-standing assumptions of the conventional savanna paradigm and aims to provide a coherent, falsifiable model that offers new explanations for otherwise disconnected observations, including the Eurasian Miocene ape record, the absence of PtERV infection in humans, the unique morphology of Homo erectus, and the remarkable suite of morphological, physiological and behavioral traits that distinguish humans from other great apes.