Did Humans Emerge “Out of Asia”?

The phrase ‘out of Africa’ has become synonymous with the concept of early primate – and by extension, human – evolution. However, recent research challenges this view, instead indicating that primates left Asia some tens of millions of years ago and colonised Africa, where they continued their evolution.

The new findings, produced by an international team of palaeontologists, announce the discovery of new fossil primate Afrasia djijidae, a species that may signify a critical step in our early evolution. The researchers, from the US, Myanmar, Thailand, and France, suggest that Africa was colonised around 38 million years ago by more primitive Asian primates such as Afrasia, supporting an ‘out of Asia’ evolution for anthropoids (a group including humans, monkeys, and apes).

Research has shown that human origins can be traced only to Africa. However, earlier and more primitive anthropoid fossils have been discovered in Asia, complicating our knowledge of anthropoid ancestry. Afrasia may have been the first anthropoid to make the journey to Africa, where subsequent primate evolution led to human origins.

Over a period of six years in Myanmar, four Afrasia teeth were discovered. The teeth are very similar to those of early anthropoid Afrotarsius libycus, a primate discovered in the Sahara desert of Libya that dates to around the same time. However, some early African fossils such as Afrotarsius appear to be on a different branch of the evolutionary tree to Afrasia, implying that at least 2 kinds of Asian anthropoid invaded Africa at the same time. “If you think about it in human terms, it’s like the ship that Columbus took to discover America,” says palaeontologist Dr K. Christopher Beard of the Carnegie Museum of Natural History in Pennsylvania, a member of the team. “If you imagine that it had multiple nationalities on it, that would be the analogy we’re thinking of in terms of the initial colonisation of Africa by these Asian anthropoids.” This research does not definitively show that Afrasia was the species to make this trip, but the similarity of the two species demonstrates a close link between the two continents that dates back millions of years.

The ‘out of Asia’ scenario is gaining popularity amongst primate scientists. Research in Asia has unearthed many fossils of increasing age, some spanning back to 40 million years ago – an order of magnitude greater than human evolution timescales. However, does the unearthing of Afrasia prove that primates trekked in a particular direction? “What this new find does is to demonstrate two taxa, one in each continent, that are very closely related, implying that there was interchange between Asia and Africa not long before each occurrence,” says Dr Jerry Hooker of the Natural History Museum’s Palaeontology department. “On its own, it does not indicate that the direction was from Asia to Africa.”

Hooker suggests that the similarities between Afrasia and Afrotarsius may instead represent dispersal rather than a one-way journey, made possible by globally low sea-levels. There also appear to be more evolved African anthropoids that were contemporaries of Afrotarsius, further complicating the situation. Both Beard and Hooker agree that further research is needed; the team are “really still at the beginning of this [work],” says Beard.

The search for early anthropoids and subsequent human ancestors is central to modern palaeoanthropology, and aids our understanding of various areas of history and science. “Evolution is a historical process that unfolds through time as a series of contingencies,” says Beard. “It’s absolutely reasonable to thing that if these little proto-monkeys hadn’t made their way to Africa in the first place, we might not be here talking about it today.”

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