Wikipedia and the scientific community
Current 'Aquatic Ape' Theories
The LCA divergence Model
Alister Hardy and Elaine Morgan were both supporters of the idea that, some time relatively soon after chimpanzees and early human ancestors diverged from the Last Common Ancestor (LCA) approximately 4-6 million years ago, water played a key role in shaping the line that led to Homo.
As Hardy said in his New Scientist Article in 1960:
However, opponents of this theory, such as Marc Verhaegen, suggest that the majority of differences between chimps (Pan) and Homo, came about much later, 2 My and after, and that bipedalism is not, in fact, evidence of an aquatic interlude, but rather the result of an orthograde spine inherent in all apes and attributed to aborealism (living in trees) and spending time in water part of the time to find food. As Algis Kuliukas states on his website:
Wading and The River Apes Model
Algis Kuliukas has probably done the most research on how wading may have played a role in helping our ancestors to become bipedal. He did a Masters degree at UCL in Human Evolution so that he could research this question further. According to Algis (following Morgan and Hardy) wading in shallow water is the simplest and most predictable way of getting an ape to move bipedally. In waist deep water any chimp, gorilla, orang-utan will move on two legs while in deep water. If he tried to enter the water quadrupedally, he would either have to swim, or drown. He states:
Opponents of the wading theory tend to point out that the LCA of Pan/Homo/Gorilla was already somewhat bipedal, and that once again, bipedalism is not evidence of an aquatic interlude, but rather the result of an orthograde spine inherent in all apes and attributed to aborealism (living in trees). Also, they claim that many early hominids, such as 'Lucy' and 'Ardi' were most likely bipedal most of the time, but they were not conclusively Homo ancestors.
The Aquarboreal Model
Marc Verhaegen, Stephen Munro, et al, suggest that most early apes probably lived in gallery forests, lagoons or mangrove-like swamps, and it was the combination of their orthograde spines, long arms and curved phalanges that enabled them to climb out of the water and to enter the water from the lower branches to search for food. There is more and more evidence to show that many apes will enter water to eat floating vegetation, etc. Verhaegen states:
He goes on to suggest that it was this 'aquarborealism' (living partly in the trees and partly in the water) that most likely led to a partial bipedal gait in early hominids such as Australopithecus (although they were probably no direct ancestors of Homo).
However, the Aquarboreal model talks only about the earlier stages (+/- Mio-Pliocene) of hominoid evolution. It doesn't explain how or why the majority of human 'aquatic features' came into existence. For that one needs to consider a littoral theory of Pleistocene Homo.
The Coastal Migration Model/ The Littoral Theory of Pleistocene Homo.
According to Marc Verhaegen and Stephen Munro, the essence of the Aquatic Ape Theory begins with Pleistocene Homo, who may have trekked along coasts to different continents and inland along rivers. They state that our most aquatic phase is not something that happened 6 million years ago because all the distinguishing features of Homo appear in the fossil record from 2.6 - 0.01 Ma, eg: larger brain, external nose, pachyostosis (heavy skeleton), platycephaly, platymeria (flattened thigh bones), ear exostoses, fossils among shellfish, dispersal to islands, etc. This would suggest that our most aquatic ancestor lived in the early Pleistocene, (i.e. less than 2.5 million years ago). They argue that the majority of 'human' characteristics and evidence of frequent diving appear only after 1.8 million years ago, although that could be due to the absense of Homo fossils.
Verhaegen believes that Homo erectus (or close relatives) probably lived along coasts and, at least part of the time, dived for seafood. Some populations may have trekked inland along rivers, seasonally or during interglacial periods. He says that if the most aquatic phase had ended before 3 million years ago, we would have lost most aquatic features and would certainly not suffer so much from a variety of common ailments and problems, eg: obesity, asthma, acne, cretinism, seborrhea, male pattern alopecia, vernix caseosa, vasomotor rhinitis, sinusitis, sleep apnea, Cheyne-Stokes, varicosis etc.
The Mixed Theories Model
Hardy asked the question: "Was man more aquatic in the past?" Evidence seems to suggest that our hominid ancestors have been at the very least littoral (coastal, shore or lake dwellers), for much of their existence. If it started as long ago as the LCA split, as Hardy and Morgan believed, a possible scenario may well be as follows: the first descendants of our last common ancestor lived in or near swamps or mangrove forest, much as Bonobos do today, and from there, our affinity with water began. This would explain why later descendants - Australapithecus, Ardi, Naledi, etc. - were most-likely tree-climbing bipeds who spent much of their time in the water, as well as in the trees. Later descendants, such as H. erectus, then began to spread out along the coasts and inland waterways, travelling northwards / eastwards and out of Africa as far as Dmanisi in Georgia and Java and Flores in Indonesia. H. erectus was possibly the most aquatic of all our relatives, becoming at one time so dependent on aquatic resources that he became a proficient diver and could remain underwater for longer periods than we can today. His bones, similar to those of many bottom feeding mammals such as manatees and walruses, were so much heavier than ours that he would have had difficulty running across the plains or spending large amounts of time far from water. Later Homo sapiens was then well equipped to leave the coasts as the climate cooled and head inland, making their way across the Bering straits into North America. Some of them also found their way down to Australasia.
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