Out-of-Africa wasn’t much of a tough gig

Stone tools and animal fossils from Saudi Arabia place early humans on the Arabian Peninsula over 300,000 years ago, according to a new study.   

Humans dispersed out of Africa in waves via modern-day Egypt and the Middle East. Taking a right turn, they would have ended up on the Arabian Peninsula. 

Evidence of members of the Homo lineage on the peninsula is hard to come by. The barren, wind-beaten terrain is just as unforgiving for fossil remains as it is for plants and animals living there today. But ancient lakebeds in the northern Saudi Arabian Nefud Desert are giving up some of the Peninsula’s secrets. 

A 90,000 year old Homo sapiens finger bone and stone tools that date back to 210,000 years ago hail from this region. 

The new study, published in the journal Nature Ecology and Evolution by an international team led by scientists from the Max Planck Institute for the Science of Human History, in Germany, pushed the date of human occupation back further still. 

Herbivore bones – most likely from ancient oryx – unearthed from beneath a lakebed at Ti’s al Ghadah date to between 500,000 and 300,000 years ago. 

“Ti’s al Ghadah is one of the most important palaeontological sites in the Arabian Peninsula and it currently represents the only dated collection of middle Pleistocene fossil animals in this part of the world,” says co-author Mathew Stewart, from the University of New South Wales in Australia. 

Alongside the bones: stone tools, suggesting early humans also inhabited the region at the time. 

Further clinching the connection, a close analysis of the bones turned up two ribs with hatchings and grooves “very reminiscent” of butchery marks, says Stewart, who did the analysis. 

The find pushes back the date of early humans on the Arabian Peninsula by at least 100,000 years.  

The team was also curious to know what climate these people were confronted with. Throughout the middle Pleistocene – the era between one million and 100,000 years ago – the climate on the peninsula oscillated between wetter and drier periods. Nevertheless, some believe that if early humans wandered onto the region they would have required special adaptations to the hyper-arid desert conditions they faced. 

That’s not true, according to the new analysis. By looking at carbon-13 and oxygen-18 isotopes in fossil herbivore teeth, the team paint a picture of a milder climate than today, not unlike the savannahs of east Africa. 

Carbon-13 tells indicates what the animals ate. Creatures munching through arid-adapted grasses, which use what’s called C4 photosynthesis, have a different carbon-13 profile compared to those with a diet of C3 trees, shrubs and shade-loving grasses. The fossils had carbon-13 signatures in line with an open C4 grasslands. 

But how arid was it? 

That’s where the oxygen-18 signature comes in. The more arid the environment, the greater the difference between oxygen-18 levels in animals that sip water from a lake or desert oasis – obligate drinkers – and animals that can survive on the water contained just in the plants they eat. 

In very arid environments, such as the Nefud desert of today, the difference between obligate and non-obligate drinkers is vast. That gap narrows in animals from less harsh environments.  

Analysis of the fossil bones from Ti’s al Ghadah revealed an oxygen-18 signature similar between obligate and non-obligate drinkers, a pattern similar to herbivores from modern-day Kenya, in East Africa. 

Instead of overcoming an inhospitable desert, it’s more likely that early humans simply expanded their range into another patch of land similar to the one they were used to in Africa. 

So far, the lakebeds of the Nefud are yet to give up a human skeleton large enough to determine who these people were. 

“We’re still in the dark as to what species it could have been,” says Stewart. But, he says, given the dates of the animal remains, it was likely a species that predated Homo sapiens.