An undated artist’s impression of members of the extinct archaic human species called the Denisovans seen in the landscape of Ganjia Basin on the northeastern edge of the Tibetan Plateau in China’s Gansu province, depicting some of the animals whose bones were found at Baishiya Karst Cave.
| Photo Credit: Reuters

Thousands of bone fragments discovered in a cave on the Tibetan Plateau in China are offering rare insight into the lives of Denisovans, the mysterious extinct cousins of Neanderthals and our own species, showing they hunted a wide range of animals from sheep to woolly rhinoceros in this high-altitude abode.

Researchers studied more than 2,500 bones found inside Baishiya Karst Cave, which is situated 10,760 feet (3,280 meters) above sea level and previously had yielded Denisovan fossil remains.

They used ancient protein analysis on these remains to reveal that the Denisovans exploited various animals for their meat and skins, and also excavated and identified a rib bone from a Denisovan individual dating to 48,000-32,000 years ago – the youngest Denisovan fossil yet known.

Most of the bones were identified as belonging to blue sheep, also called bharal, a goat species still seen on high slope mountains and cliffs in the Himalayas. Other bone remains came from woolly rhinos, yaks, small mammals like marmots, birds, and even from the spotted hyena, a large carnivore that prowled the region called the Ganjia Basin.

It was a grass landscape with small forested areas, teeming with life despite harsh conditions. The animals were butchered for meat, based on cut marks found on various bones, and there was evidence of bone marrow extraction and skinning activities. The researchers also found four tools fashioned from animal bone, shaped for use in processing animal carcasses.

“It is the first time we have gotten an understanding of the subsistence behaviors of Denisovans, and it shows us they were highly capable of accessing and utilizing a wide range of animal resources,” said University of Copenhagen molecular anthropologist Frido Welker, one of the leaders of the research published on Wednesday in the journal Nature.

“I think the diverse animal remains found in Baishiya Karst Cave suggest that this location offered relatively better resources compared with the neighboring higher Tibetan Plateau to the west and the Chinese Loess Plateau to the north, especially in the glacial period,” said archeologist Dongju Zhang of Lanzhou University in China, another of the study leaders.

The existence of Denisovans was unknown until researchers in 2010 announced the discovery of their remains in Denisova Cave in Siberia, with genetic evidence showing them to be a sister group to Neanderthals, the stoutly built extinct archaic humans who inhabited parts of Eurasia. Both experienced significant interactions with Homo sapiens, including interbreeding, before vanishing soon after for reasons not fully understood.

“From genetics, we know they diverged from Neanderthals around 400,000 years ago,” Welker said.

Denisovans are known only from dental remains and bone fragments from the Baishiya Karst and Denisova caves and Cobra Cave in Laos, though their existence at those three far-flung locations demonstrates a wide geographic dispersal.

Their presence at a high latitude in Siberia, a high altitude on the Tibetan Plateau and a subtropical location in Laos “implies that Denisovans had high flexibility to adapt to different environments,” Zhang said.

A lower jaw of a Denisovan adolescent previously found at Baishiya Karst is 160,000 years old. The researchers suspect Denisovans were present there as far back as 200,000 years ago. The newly identified rib fragment shows that Denisovans still existed as recently as 48,000-32,000 years ago.

“We don’t know if the rib was from an adult or a child, nor its genetic sex. It is the first time a rib specimen has been identified as a Denisovan. Previous remains are all dental or cranial or mandibular (lower jaw),” Welker said.

Our species, Homo sapiens, did not populate the Tibetan Plateau until about 40,000 years ago, having first appeared in Africa a bit more than 300,000 years ago.

So what happened to the Denisovans?

“Great question. We know so little,” Welker said. “We know that Denisovans interbred with modern humans. We know that based on some Denisovan DNA that is present in the genomes of some modern humans living today. But when, where and why Denisovans ultimately went extinct, that we don’t know anything about.”

A novel genomic analysis technique has helped reveal the reasons for a ‘bottleneck’ in the growth of the human population that almost wiped out the chance for humankind as it exists today.
| Photo Credit: AFP

A novel genomic analysis technique has helped reveal the reasons for a ‘bottleneck’ in the growth of the human population that almost wiped out the chance for humankind as it exists today, scientists reported in a study published in Science.

The findings indicate that the early population of human ancestors went through a period in which approximately 1,280 breeding individuals were able to sustain a population for about 117,000 years, the researchers from China, Italy, and the U.S. said.

They were able to determine demographic characteristics using modern-day human genome sequences from 3,154 individuals and a new analytical method called fast infinitesimal time coalescent process (FitCoal).

FitCoal helped the researchers calculate a probable population size through history based on contemporary sequences. They reported as a result that early human ancestors experienced extreme loss of life and, therefore, loss of genetic diversity.

Giorgio Manzi, an anthropologist at Sapienza University of Rome and a coauthor of the paper, said that the gap in “the African and Eurasian fossil records” can be explained by this “bottleneck in the Early Stone Age”.

The reasons suggested for this downturn in the size of the human ancestral population include glaciation events, leading to changes in temperature and severe droughts, and the loss of other species, potentially those that were food sources for ancestral humans.

An estimated 65.85% of humans’ current genetic diversity may have been lost in this period, in the early to middle Pleistocene era (from two million to 11,000 years ago), and the prolonged period of a minimal number of breeding individuals could have threatened humankind as we know it today, the researchers said in their study.

However, the bottleneck also seemingly contributed to a speciation event in which two ancestral chromosomes may have converged to form chromosome 2 in modern humans, the researchers said.

“The novel finding opens a new field in human evolution because it evokes many questions, such as the places where these individuals lived, how they overcame the catastrophic [climatic] changes, and whether natural selection during the bottleneck accelerated the evolution of the human brain,” said senior author Yi-Hsuan Pan, a researcher of evolutionary and functional genomics at East China Normal University, China.

Now that there is reason to believe that humans grappled with a struggle 930,000-813,000 years ago, researchers can continue digging to reveal how such a small population persisted in presumably dangerous conditions, the study said.

Humankind’s rebound is expected to have been due to the use of fire and the arrival of more favourable climates.