Australopiths (e.g. "Lucy") are not human ancestors, but extinct relatives of Pan or Gorilla.

What is it about?

The dominant paradigm re. human evolution since the split c 5 mill.yrs ago with Pan (chimps+bonobos) considers australopiths as "hominins": the closest relatives of Homo. Historically, this paradigm started from the assumption that the Homo/Pan/Gorilla ancestor were knuckle-walking apes that evolved into the fully upright (orthograde), obligate bipedal genus Homo, whereas Pan & Gorilla remained knuckle-walkers. Obligate terrestrial upright bipedalism (unique for humans) is an odd locomotor behaviour for a primate, so it had become generally believed that a drier African climate had caused deforestation, which had forced our ancestors to develop upright bipedalism as an adaptation to living on open grassland savanna. This view - already held by Lamarck & Darwin - appeared most parsimonious in the almost complete absence of fossils. The discovery in the 20th cent. of australopith fossils - bipedal apes with small brains - in open country in S- & E-Africa corroborated this savanna paradigm: australopiths were considered human ancestors. But it is now recognized e.g. (1) most australopiths instead lived in environments incl. wetlands, (2) they had several climbing adaptations, (3) the fossil ape spp older than australopiths for which postcranial remains have been described (Morotopithecus, Sahelanthropus, Orrorin, Ardipithecus) were not knuckle-walking: upright posture/gait is already present to different degrees even in Miocene apes, (4) knuckle-walking is not a primitive trait, but has evolved in parallel in both Pan & Gorilla. Concl.: australopiths are not transitional between semi-erect ancestors & upright bipedal humans, but are intermediate between more upright ancestors & extant semi-erect African apes: hypotheses that attempt to explain how semi-erect Homo/Pan ancestors transitioned into bipedal australopiths living in savannas appear to be ill-conceived - superfluous from the very start. We review the numerous similarities of australopiths with extant African apes: they are possibly not our direct ancestors: we may have been barking up the wrong ancestral tree, for almost a century.

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Why is it important?

A very different view on ape+human evolution. Getting rid of australopiths as our ancestors may allow us to tell a very different story of human evolution: we originated not on the savanna as upright running apes, but evolved as apes swimming + diving in shallow (coastal) waters. Hence our large brains, fur-loss, subcutaneous fat layer, voluntary breath control etc., that are better explained as aquatic adaptations. See "Was Man More Aquatic in the Past? Fifty Years after Alister Hardy. Waterside Hypotheses of Human Evolution" https://www.growkudos.com/publications/10.2174%252F97816080524481110101/reader

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