genomes

‘Ghost’ Ancestors: African DNA Study Detects Mysterious Human Species

The discovery provides the latest evidence of humankind’s complicated genetic ancestry.

Washington: Scientists examining the genomes of West Africans have detected signs that a mysterious extinct human species interbred with our own species tens of thousands of years ago in Africa, the latest evidence of humankind’s complicated genetic ancestry.

The study indicated that present-day West Africans trace a substantial proportion, some 2% to 19%, of their genetic ancestry to an extinct human species – what the researchers called a “ghost population.”

“We estimate interbreeding occurred approximately 43,000 years ago, with large intervals of uncertainty,” said University of California, Los Angeles (UCLA) human genetics and computer science professor Sriram Sankararaman, who led the study published this week in the journal Science Advances.

Homo sapiens first appeared a bit more than 300,000 years ago in Africa and later spread worldwide, encountering other human species in Eurasia that have since gone extinct including the Neanderthals and the lesser-known Denisovans.

Previous genetic research showed that our species interbred with both the Neanderthals and Denisovans, with modern human populations outside of Africa still carrying DNA from both. But while there is an ample fossil record of the Neanderthals and a few fossils of Denisovans, the newly identified “ghost population” is more enigmatic.

Asked what details are known about this population, Sankararaman said, “Not much at this stage. We don’t know where this population might have lived, whether it corresponds to known fossils, and what its ultimate fate was,” Sankararaman added.

Sankararaman said this extinct species seems to have diverged roughly 650,000 years ago from the evolutionary line that led to Homo sapiens, before the evolutionary split between the lineages that led to our species and to the Neanderthals.

The researchers examined genomic data from hundreds of West Africans including the Yoruba people of Nigeria and Benin and the Mende people of Sierra Leone, and then compared that with Neanderthal and Denisovan genomes. They found DNA segments in the West Africans that could best be explained by ancestral interbreeding with an unknown member of the human family tree that led to what is called genetic “introgression.”

It is unclear if West Africans derived any genetic benefits from this long-ago gene flow.

“We are beginning to learn more about the impact of DNA from archaic hominins on human biology,” Sankararaman said, using a term referring to extinct human species. “We now know that both Neanderthal and Denisovan DNA was deleterious in general but there were some genes where this DNA had an adaptive impact. For example, altitude adaptation in Tibetans was likely facilitated by a Denisovan introgressed gene.”

Stone-Age ‘Chewing Gum’ Reveals Human DNA

A lump of gum has revealed a dark-skinned, blue-eyed, hunter-gatherer who inhabited Scandinavia thousands of years ago. This is the first time a full ancient human genome has been extracted from anything other than bone.

Researchers from Denmark have extracted a complete human DNA sample from a piece of birch bark tar believed to be more than 5,000 years old and used as chewing-gum in the Neolithic era.

The DNA revealed that the young female living in southern Denmark during the Stone Age probably had dark skin, dark hair, and blue eyes.

“It is the first time that an entire ancient human genome has been extracted from anything other than human bones,” Hannes Schroeder, a molecular anthropologist at the University of Copenhagen, told French news agency AFP.

Schroeder, the co-author of the study, published her findings in the review Nature Communications.

Also read: Timeline for Speech Evolution Pushed Back 27 Million Years

The bark was found during an archaeological dig at Syltholm on Lolland Island, southern Denmark.

The team of scientists also concluded that the girl was genetically more closely related to hunter-gatherers from mainland Europe than those living in central Scandinavia at the time.

The DNA could also indicate what the source had last eaten and the kinds of bacteria in her mouth.

In addition to the DNA, the team also found genetic materials from hazelnut and ducks, presumed traces of a recent meal and around 40 types of microbes, confirming what archaeologists already know about the people who lived in southern Denmark 5,000 years ago.

Well-preserved

Researchers also detected pathogens such as the Epstein-Barr virus, which can cause glandular fever, but does not necessarily mean she was ill as the virus can be present without causing illness.

Also read: The Science of How Human Bodies Decay

“It can help us understand how pathogens have evolved and spread over time … it could help us predict how the pathogen will behave in the future and how it might be contained or eradicated,” Schroeder said.

However, the scientists are not entirely sure why the source chewed the bark, saying that while it could have been simply used as chewing gum, she might have also been chewing it as a method to turn it into a type of glue, to clean her teeth, or even to fight off hunger.

It is impossible to know her age from the DNA, but the scientists concluded that given children seemed to chew birch tar, it is likely that she was young.

“Syltholm is completely unique,” Tehis Jensen, one of the authors, said. “Almost everything is sealed in mud, which means that the preservation of organic remains is absolutely phenomenal.”

The article was originally published on DW. You can read it here.

Komodo Dragons Have a Famous Endurance. Scientists Are Looking for Its Roots in Their Genes.

Genetic adaptations involving the function of the mitochondria may have resulted in the amplification of the lizard’s aerobic capacity.

Washington: Scientists have mapped the genome of the Komodo dragon, the world’s largest lizard, discovering intriguing secrets behind the impressive speed and endurance these cold-blooded predators muster by ratcheting up their metabolism to mammal-like levels.

Researchers said on Monday they pinpointed crucial genetic adaptations that may underpin the tenaciousness of these lizards that inhabit several Indonesian islands including Komodo and bring down prey as big as a water buffalo with a venomous bite.

Komodo dragons reach up to about 10 feet (three metres) long, possess curved and serrated teeth, a yellow forked tongue, strong limbs and a long tail.

“This is an apex predator living on isolated islands, and it’s absolutely gigantic. It’s just an awesome animal,” said Benoit Bruneau, director of the Gladstone Institute of Cardiovascular Disease, affiliated with the University of California, San Francisco, one of the senior authors of the study published in the journal Nature Ecology & Evolution.

Also read: We Don’t Really Know What ‘Species’ Are. Here’s Why.

“Reptiles are kind of like a playground for evolution. There is so much diversity in size and form and behaviour and their physiology,” Bruneau added.

The team sequenced the genome using blood samples of two Komodo dragons housed at Zoo Atlanta, named Slasher and Rinca.

A 6.6 feet Komodo dragon at the national zoo in Pretoria. Photo: Reuters/Salim Henry/Files

The researchers discovered genetic adaptations involving the function of the mitochondria, the power generators of cells that are critical in governing the function of cardiac and other muscles, that may amplify the lizard’s aerobic capacity.

As cold-blooded creatures, reptiles typically lack in aerobic capacity, rapidly becoming exhausted after physical exertions, unlike warm-blooded mammals. Komodo dragons, an exception among reptiles, can achieve near-mammalian metabolism.

The researchers also found adaptations involving genes that control chemical sensors involved in an advanced sensory system that lets Komodo dragons detect hormones, the body’s chemical messengers, and pheromones, chemicals released particularly by mammals that serve as cues to other members of their species.

These adaptations may help Komodo dragons find prey over long distances, added study co-author Katherine Pollard, director of the Gladstone Institute of Data Science & Biotechnology.

One component of the Komodo dragon’s venom is an anti-coagulant compound that prevents the victim’s blood from clotting, causing it to bleed to death. The researchers found adaptations in Komodo dragon genes involved in coagulation that make these lizards immune from the venom anti-coagulant, protecting them from bleeding to death when attacked by another of their own species.

“When two males are fighting one another,” Bruneau said, “it is one impressive show of force.”