Stephanorhinus
Artist’s rendering of a Stephanorhinus, dated 1916

By Kristine A. Garland

In a scientific breakthrough, researchers have extracted genetic material, more than a million years old, from the tooth of a rhinoceros ancestor. The find could very well lead to a better understanding of human evolution.

Researchers from the University of Copenhagen and the University of Cambridge have used a technique that allowed them to extract and sequence a complete set of ancient proteins from the dental enamel of the extinct Stephanorhinus, a genus of two-horned rhinoceros native to northern Eurasia.

This extraction of ancient proteins allows researchers to retrieve genetic information from fossils so old that their DNA has not survived.

“Dental enamel is the strongest material you see in vertebrates, and this is why it preserves particularly well in ancient fossils,” says Dr. Enrico Cappellini, in a telephone interview with Incisor. “That is why the fossil record is particularly rich with teeth.”

Dr. Cappellini
Dr. Enrico Cappellini

Dr. Cappellini is the lead author on the research originally published in Nature (September 2019). He is an associate professor at the University of Copenhagen, and affiliated with the Centre for GeoGenetics, Natural History Museum of Denmark

This extraction of ancient proteins allows researchers to retrieve genetic information from fossils so old that their DNA has not survived. DNA typically only survives approximately 500,000 years in temperate environments, and up to about 800,000 years in frozen soil environments like permafrost. These where previously the limits of when and where researchers could retrieve ancient genetic information.

By sequencing ancient proteins from dental enamel, researchers can retrieve genetic information and use it to reconstruct the evolutionary relationships between the species the fossil belongs to and current organisms with which it is closely associated.

“This is the novel component [of this research]. We cannot recover ancient DNA from our samples. We tried the recovery of ancient DNA, and it failed. This was not surprising because the material is too old to return ancient DNA,” Dr. Cappellini told Incisor. “What we found is that we can retrieve proteins, which are basically the first expression of genetic information encoded in DNA.”

A Game-Changer

In this case, the research is being called a “game-changer” because researchers can now retrieve ancient genetic information going back almost two million years by sequencing ancient proteins.

“This is a significant expansion of coverage that we can reach,” Dr. Cappellini explains. “We open a new window to record genetic information.”

By sequencing ancient proteins from dental enamel, researchers can retrieve genetic information and use it to reconstruct the evolutionary relationships between the species the fossil belongs to and current organisms with which it is closely associated.

“Before this research, it was only possible to find relationships between these fossils and closely related living organisms by using the anatomy and morphology [form and structure] of these fossils,” Dr. Cappellini says. “Now, by retrieving ancient proteins from dental enamel and sequencing them, we can obtain genetic information that we can compare with the sequencing of proteins from living organisms.”

Lucy Public Domain
“Lucy.” Photo from Cantonal Museum of Geology

Dr. Cappellini says that the most interesting potential application of this technology could contribute to a better understanding of human evolution. For example, the chimpanzee is the closest living organism to humans, he explains, and the evolutionary branch that led to chimpanzees diverged around six-to-seven million years ago.

“If you consider that with DNA you could cover—let’s say only the last ½ million years—only about the last 10% of the branch that goes from the common ancestor with us to chimps, this means that approximately 90% of the path that leads to us is unchartered from a molecular point of view,” he says.

With the newfound possibility to sequence ancient proteins, Dr. Cappellini says researchers can cover a more significant fraction of that path and obtain a better understanding of the relationships between humans and other species.

“For example, what’s the relationship between the more distant species like Australopithecus, the famous fossil, ‘Lucy’?” he asks. “We know it’s different from us, but we don’t know what the relation is because we don’t have genetic information from fossils like Lucy.”

 

Author: Contributing writer Kristine A. Garland received her MA in Journalism from New York University’s Science, Health and Environmental Program. She serves in the U.S. Navy as a public affairs officer. 

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