Mud DNA means we can detect ancient humans even without fossils

27 April 2017
 
By Michael Le Page

We have an astonishing new way to study our early human ancestors: looking for their DNA in ancient sediments in places such as caves.

A team of researchers has found the DNA of Neanderthals and Denisovans in some of the sites where they are known to have lived.

“I think we show convincingly that these sequences are authentic,” says lead author Viviane Slon of the Max Planck Institute for Evolutionary Anthropology in Germany.
 
The approach can now be used to find out whether early humans were present even when no bones have been found – and what kind of humans they were. It might also help resolve the debate about when the Americas were first inhabited by people, for instance.
Universe in a gram of mud

Just about any sample of soil or water is full of DNA from all kinds of organisms. Sequencing this “environmental DNA” is an increasingly powerful tool for studying ecosystems.

For instance, biologists were recently able to identify several caves where “baby dragons”, or olms, live simply by analysing the water flowing out of them.

In sediments buried in cool caves and in permafrost, this environmental DNA can survive for up to 700,000 years. In 2003, a team led by Eske Willerslev, now at the University of Cambridge, was the first to show that it was possible to find ancient DNA from species like the woolly mammoth, in frozen mud in Siberian permafrost.

Now Slon’s team has shown that ancient human DNA can survive in sediments too. Her team sequenced all the DNA present in sediment samples from sites where hominins lived, such as Denisova cave in Russia. The biologists then used short pieces of modern human mitochondrial DNA to extract longer bits of DNA containing a matching sequence from the samples.

The team looked for DNA from the energy-generating mitochondria within our cells, because they each contain the same DNA and there are hundreds per cell, so it is the type most likely to survive.



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Study finds bonobos may be better representation of the last common ancestor with humans than common chimpanzees

April 29, 2017

A new study examining the muscular system of bonobos provides firsthand evidence that the rare great ape species may be more closely linked, anatomically, to human ancestors than common chimpanzees. Previous research suggested this theory at the molecular level, but this is the first study to compare in detail the anatomy of the three species.

"Bonobo muscles have changed least, which means they are the closest we can get to having a 'living' ancestor," said Bernard Wood, professor of human origins at the GW Center for the Advanced Study of Human Paleobiology.

Scientists believe that modern human and common chimpanzee/bonobo lineages split about 8 million years ago with the two great ape species splitting about 2 million years ago. As common chimpanzees and bonobos evolved after their split, they developed different traits and physical characteristics, even though they remained geographically relatively close, with their main division being the Congo River. Because of this, researchers have been curious as to what those differences are and how they compare to humans. By studying the muscles of bonobos (which indicates how they physically function), the team was able to discover that they are more closely related to human anatomy than common chimpanzees, in the sense that their muscles have changed less than they have in common chimpanzees.

Earlier studies examined the DNA similarities and differences between bonobos and common chimpanzees, but this was the first study to compare the muscles of the three species.

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A Grassy Trend in Human Ancestors' Diets

June 3, 2013 — Most apes eat leaves and fruits from trees and shrubs. New studies spearheaded by the University of Utah show that human ancestors expanded their menu 3.5 million years ago, adding tropical grasses and sedges to an ape-like diet and setting the stage for our modern diet of grains, grasses, and meat and dairy from grazing animals.

In four new studies of carbon isotopes in fossilized tooth enamel from scores of human ancestors and baboons in Africa from 4 million to 10,000 years ago, a team of two dozen researchers found a surprise increase in the consumption of grasses and sedges -- plants that resemble grasses and rushes but have stems and triangular cross sections.

"At last, we have a look at 4 million years of the dietary evolution of humans and their ancestors," says University of Utah geochemist Thure Cerling, principal author of two of the four new studies published online June 3 by the journalProceedings of the National Academy of Sciences. Most funding was from the National Science Foundation.

"For a long time, primates stuck by the old restaurants -- leaves and fruits -- and by 3.5 million years ago, they started exploring new diet possibilities -- tropical grasses and sedges -- that grazing animals discovered a long time before, about 10 million years ago" when African savanna began expanding, Cerling says. "Tropical grasses provided a new set of restaurants. We see an increasing reliance on this new resource by human ancestors that most primates still don't use today."

Grassy savannas and grassy woodlands in East Africa were widespread by 6 million to 7 million years ago. It is a major question why human ancestors didn't seriously start exploiting savanna grasses until less than 4 million years ago.

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Ancient walking gets weirder

The simple act of walking continues to take strange detours among ancient human ancestors. 


To wit, 1.5 million-year-old footprints excavated in Africa, initially thought to reflect a thoroughly modern walking style, were instead made by individuals that walked differently than people today do, researchers reported April 13 at the annual meeting of the American Association of Physical Anthropologists. 

And findings presented April 12 at the meeting revealed the surprisingly apelike qualities of foot fossils from a 2 million-year-old species that some researchers regard as the root of the Homo genus. 

These reports come on the heels of evidence that a previously unknown member of the human evolutionary family 3.4 million years ago possessed a gorillalike grasping big toe and an ungainly stride. 

Depth measurements of the African footprints, discovered at Kenya’s Ileret site, differ at 10 landmarks from the footprints of people who live in that area today, said graduate student Kevin Hatala of George Washington University in Washington, D.C. 


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