Friday, 30 January 2015

Modern humans in the Levantine corridor 55,000 years ago

But did they encounter Neanderthals?

Hershkovitz et al report the discovery report the discovery of a partial skullcap at Manot Cave, Western Galilee. The skullcap has been dated by uranium/thorium methods to 54,700 +/- 5,500 years old. Its describers note archaic features such an occipital bun but claim that it is ‘unequivocally modern’. Although the occipital bun is associated with Neanderthals, it was also common among early Upper Palaeolithic modern humans. The describers admit that taxonomic significance of Manot 1’s mosaic of archaic and modern features is unclear, but note that hominins with similar combinations are known from the fossil record of the Levant and sub-Saharan Africa until and even after 35,000 years ago. Geometric morphometric studies align Manot 1 with recent and Upper Palaeolithic modern humans, but it is more distant from some (but not all) Middle Palaeolithic modern humans.

Although modern humans were in the Levant around 115,000 years ago, it is believed that they did not remain there after 75,000 years ago following the onset of the cold, arid conditions of Marine Isotope Stage 4. By 70,000 years ago, Neanderthals had re-occupied the region: the two human species ‘time-shared’ the region as the climate alternated between warm, wet and cold, arid. It has been suggested that the Neanderthal presence persisted until 50,000 or even 45,000 years ago.

If modern humans were in the region no later than around 50,000 years ago, the implication is that the two human species might have come into contact. The authors of the Manot 1 report speculate that its’ mosaic of archaic and modern features could indicate that it is a Neanderthal/modern hybrid.

While this view is certainly feasible, it is not without problems. Many of the radiocarbon dates placing Neanderthals in the Levant at the time in question were obtained in the 1960s, and the true dates may be nearer 60,000 years ago. It is therefore possible that the two human species missed each other by several thousand years; this would be consistent with the ‘time-share’ view that their respective ranges ebbed and flowed in sequence with warm/cold climatic cycles.

On the other hand, it is certainly possible that descendants of the Manot population later migrated to Europe, where the latest radiocarbon dates suggest that modern humans associated with the Aurignacian culture arrived around 46,000 years ago.


1. Hershkovitz, I. et al., Levantine cranium from Manot Cave (Israel) foreshadows the first European modern humans. Nature (2015).

Tuesday, 27 January 2015

Archaic human recovered from seabed off western coast of Taiwan

Could partial lower jawbone be from a Denisovan – or an entirely new species?

A partial fossil human jawbone from Taiwan is reportedly the first archaic hominin to be found there. The jawbone was dredged by a fishing net from the 60 to 120 m (200 to 400 ft.) deep Penghu Channel, 25 km (15.5 miles) of the island’s western coast. Also recovered were vertebrate fossils known as the terminal Middle/Late Pleistocene ‘Penghu fauna’. Both Taiwan and the Penghu Channel were part of the Asian mainland during Pleistocene episodes of lowered sea levels. The jawbone found its way to an antique shop in Tainan City, where it was purchased by a local man who in turn donated it to the National Museum of Natural Science of Taiwan.

The nature of its recovery means that there is no stratigraphic data by which the Penghu 1 jawbone can be dated. Accordingly, researchers measured its fluorine and sodium content in relation to that of other Penghu fossils. Fluorine, deriving from the surroundings, tends to accumulate slowly over time in buried bones; sodium on the other hand exists at about one percent in the bones of living vertebrates, but decreases when they are fossilised. By this means, the researchers matched Penghu 1 with fossil remains of Crocuta crocuta ultima, an extinct Eurasian subspecies of the spotted hyena that reached northern China between 500,000 and 250,000 years ago, but did not reach southern China until 240,000 years ago. There were episodes of lowered sea levels between 190,000 to 130,000 years ago and from 70,000 to 10,000 years ago; Penghu 1 probably dates to one of these two intervals.

Penghu 1 is identified as archaic by its relatively large molars and premolars, and by its lack of a chin. The short and relatively wide shape of its dental arcade is derived in comparison to the earliest humans (Homo habilis and the Dmanisi hominins), but other than that it cannot readily be assigned to any particular archaic human species. The second molar is larger than those of other archaic Asian hominins, and the low, thick body is closer to some examples African and European Homo from 400,000 years ago than to Early/Middle Pleistocene Asian Homo, with the exception of the 400,000-year-old Chinese Hexian Homo erectus remains.

The large second molar suggests Denisovan affinities in M2 crown size, but unfortunately no Denisovan lower jawbones or lower M2 teeth have yet been found for comparison. Not until we have a Denisovan lower jawbone that can be identified as such by genetic means will we have a better idea if Penghu 1 belonged to a Denisovan.  Nor can we rule out the possibility that Penghu 1 represents a completely new archaic human species.

Chang, C. et al., The first archaic Homo from Taiwan. Nature Communications 6, 6037 (2015).

Friday, 16 January 2015

Apes adapted to metabolising ethanol ten million years ago

Humans were preadapted to dietary alcohol consumption

Alcohol has played a prominent role in human affairs throughout recorded history, but how far does its use go back? One view is that humans were teetotal until the advent of agriculture 9,000 years ago, when storage of food surpluses soon led to the invention of fermentation techniques. This model attributes the social problems associated with alcohol to the human metabolism not yet having had enough time to fully adapt to its consumption.

An alternative view is that primates became adapted to alcohol through eating fruit that was partially fermented through yeast infestation. Such fleshy fruits first appeared 80 million years ago, very early on in primate history and before the dinosaurs became extinct. The ‘evolutionary hangover’ model posits that arboreal primates foraging in trees became attracted to the smell of slightly-fermented fruit that might otherwise have gone unnoticed. This adaptation ceased to be beneficial once the attraction was turned to more strongly alcoholic drinks.

To resolve the issue, researchers resurrected digestive alcohol dehydrogenases (ADH4) enzymes from our primate ancestors to explore the history of primate interactions with ethanol. They reconstructed the evolutionary history of the ADH4 family of enzymes using ADH4 genes from 28 different mammals, including 17 primates. They synthesised nine of the ADH4 enzymes, from which they deduced that an ethanol-metabolising form was not yet appeared when orangutans diverged from gorillas, chimps and humans, but was present in the last common ancestor of gorillas, chimps and humans about ten million years ago.

The timing coincides with a shift to apes spending more time on the ground. It is likely that they began eating overripe, highly-fermented fruit that fell to the forest floor. At this time, apes faced growing competition from monkeys due to the ability of the latter to eat unripe fruit before it became suitable for consumption by apes. The ability to eat overripe fruit without becoming inebriated might have been an evolutionary adaptation to the problem.

It’s something to think about over a few beers….

References:Carrigan, M. et al., Hominids adapted to metabolize ethanol long before human-directed fermentation. PNAS 112 (2), 458-463 (2015).