How a Crested Rat Sheds Light on Human Migration Out of Africa

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DNA extracted from the bones of a rodent living in the Judean Desert 100 years ago indicates that there was an "ecological corridor" between Africa and the Levant
DNA extracted from the bones of a rodent living in the Judean Desert 100 years ago indicates that there was an "ecological corridor" between Africa and the Levant Credit: Haifa Unviersity

There is no question that early modern humans reached Europe from Africa via what is today Israel, and likely also through other routes too. The rub is that much of the journey passes through what are today the Saharo-Arabian deserts. The question is whether modern humans achieved behavioral and/or technological advances enabling them to survive and surpass the deserts, or whether they simply trekked through green corridors created by periodic climatic swings.

Now a study published in PNAS by a large international team suggests support for the green corridors theory, based on the long-dead body of a crested rat who lived about 42,000 years ago in what is today Israel’s arid Judean Desert.

The crested rat was identified by DNA analysis, making this the oldest DNA analyzed (successfully) so far in the Levant, according to University of Haifa researchers. Elsewhere scientists have sequenced much older specimens, including a million-year-old mammoth, but the conditions in the Levant are not suitable to preserving ancient bones of the quality necessary to preserve DNA.

Crested rats do not do deserts. The identification of the fossil rodent as the (sadly extinct) subspecies Lophiomys imhausi maremortum, indicates that back then, the land stretching between Africa and Europe was a true ecological corridor. It had more rain and was greener than it is today, and was able to support life forms exiting Africa.

Basically, where the crested rat could go, so could modern humans without need for special adaptation.

A poisonous rodent

The crested rat, aka the maned rat, is not a rat per se, though they’re in the same superfamily. They are furry and pretty, with black and white stripes along the length of their bodies, and have bushy tails, not naked tails like rats. When triggered, the fur along their spines puffs up like a mohawk hairdo.

In contrast to alarmed cats puffing up, the crested rat’s display is more than a size-related deterrent. The rodent bites off bits of the poisonous East African tree Acokanthera and spits the toxin onto its spinal fur, effectively rendering itself poisonous. It has special “honeycomb”-structured hairs in its mohawk adornment that hold the poison efficiently.

African crested rat applies its poisonCredit: Sara Weinstein, Youtube

So that is the crested rat. A surviving subspecies lives in East Africa, and thus if a crested rat lived 42,000 years ago in what is today the Judean Desert, one may infer the region was like East Africa is now – i.e., not barren desert, the researchers suggest. So it would have been possible for life forms to walk from Africa to Eurasia, as is indicated by “species distribution models” that show habitats connecting Africa and the Levant continuously during the last interglacial period, 116,000 to 129,000 years ago.

To add proportion, the fossil crested rat bones were found among other animal remains that date at the earliest to about 103,000 years, University of Haifa team leader Nimrod Marom, an archaeozoologist, explains to Haaretz. The rodent itself lived perhaps 42,000 years ago but the subspecies as a whole apparently spread to the Judean region earlier, i.e., 100,000 years ago.

Big animals like elephants and antelopes can migrate vast distances quite rapidly. So can aviating creatures. Not so the crested rat – how far could it go on its little legs? It couldn’t bound above the desert wastelands, and that in and of itself strongly indicates there was a period of a convenient corridor that lasted tens of thousands of years.

The dating of the fossil of the Israeli crested rat fits with genetic analyses indicating that the rodent’s lineages – the modern one in East Africa today and the extinct Levantine one – split from one another around 100,000 years ago. Since that time, they developed separately, Marom says.

He qualifies that all these ancient dates and periods are cited with hefty standard deviations: When talking of an animal living 42,000 or 100,000 years ago, the deviation in either direction could be thousands of years. In other words, theoretically the arrival of the crested rat in the land could correspond with the time frame of Israeli sites such as Qafzeh and Es Skhul, and Nesher Ramla, where remains of hominins with a mix of modern and archaic features have been found, dating to about  80,000 to 130,000 years ago.

Skull of crested rat found in Israeli cave, from about 42,000 years agoCredit: Ignacio Lazagabaster

That said, the hominins in Qafzeh and Skhul may have belonged to a hominin variant recently identified as Homo Nesher Ramla, , which may actually be the last gasp of a hominin species ancestral to Neanderthals.

Does all this mean humans accompanied the rodent on its trek? Not necessarily, it just means they could have without recourse to some new technology or brainwave. Hominins have been leaving Africa for almost two million years, if not more. Anatomically, modern humans began to evolve in Africa apparently about half a million years ago. Then what?

Israel Hershkovitz of Tel Aviv University, an expert on human evolution who isn’t connected with the Haifa study, adds that in his opinion, it isn’t that early modern humans left Africa in vast waves – they trickled out. The evidence in Israel shows that Homo sapiens first got here around 250,000 years ago, the professor says.

But there is no evidence of Homo sapiens occupation in Israel between 60,000 and 90,000 years ago – or maybe we just haven’t found it, Hershkovitz adds. Or they weren’t here, for some reason. Going by the crested rat, they could have made the trek.

Around 70,000 years ago Neanderthals arrived in what is today Israel, descending south from Eurasia, and 60,000 years ago, modern humans returned. The two populations met and following that, Neanderthals disappeared and sapiens reigned supreme. Possibly with crested rats watching them oh-so-cautiously from the caves.

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