DNA Proteins Revealing Information About Human Evolution

Since the advent of population genetics and modern techniques to examine DNA, research has focused on, first, Mitochondrial DNA and then nuclear DNA.  Now we have another weapon in our arsenal.  Matthew Warren of Nature News relates new research done on palaeoproteomics.  This is the study of proteins found in fossilized human ancestors.  How is this possible, you ask?

Some time in the past 160,000 years or so, the remains of an ancient human ended up in a cave high on the Tibetan Plateau in China. Perhaps the individual died there, or parts were taken there by its kin or an animal scavenger. In just a few years, the flesh disappeared and the bones started to deteriorate. Then millennia dripped by. Glaciers retreated and then returned and retreated again, and all that was left behind was a bit of jawbone with some teeth. The bone gradually became coated in a mineral crust, and the DNA from this ancient ancestor was lost to time and weather. But some signal from the past persisted.

Deep in the hominin’s teeth, proteins lingered, degraded but still identifiable. When scientists analysed them earlier this year, they detected collagen, a structural support protein found in bone and other tissues. And in its chemical signature was a single amino-acid variant that isn’t present in the collagen of modern humans or Neanderthals — instead, it flagged the jawbone as belonging to a member of the mysterious hominin group called Denisovans. The discovery of a Denisovan in China was a major landmark. It was the first individual found outside Denisova Cave in Siberia, where all other remains of its kind had previously been identified. And the site’s location on the Tibetan Plateau — more than 3,000 metres above sea level — suggested that Denisovans had been able to live in very cold, low-oxygen environments.

As the author notes, this kind of research has opened many other doors that, up until now, have been shut to researchers. The realization that proteins have much longer staying power than DNA could radically reshape our understanding of human evolution:

Previously, scientists had recovered proteins from 1.8-million-year-old animal teeth and a 3.8-million-year-old eggshell. Now, they hope that palaeoproteomics could be used to provide insights about other ancient hominin fossils that have lost all traces of DNA — from Homo erectus, which roamed parts of the world from about 1.9 million to 140,000 years ago, to Homo floresiensis, the diminutive ‘hobbit’ species that lived in Indonesia as recently as 60,000 years ago. By looking at variations in these proteins, scientists hope to answer long-standing questions about the evolution of ancient human groups, such as which lineages were direct ancestors of Homo sapiens.

Whether that level of resolution will ever be possible remains to be seen, especially given that the modus operandi of modern palaeontology is focused on clade relationships. It will be interesting to see.

The Ancient History of Neanderthals in Europe

The Max Planck Society has a post in PhysOrg, a highly-regarded science site, on the history of Neandertals (they have used the old spelling). 

Researchers at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, have retrieved nuclear genome sequences from the femur of a male Neanderthal discovered in 1937 in Hohlenstein-Stadel Cave, Germany, and from the maxillary bone of a Neanderthal girl found in 1993 in Scladina Cave, Belgium. Both Neanderthals lived around 120,000 years ago, and therefore predate most of the Neanderthals whose genomes have been sequenced to date.

Perhaps the most interesting aspect of the research was how much evolution within Neandertals was revealed:

Intriguingly, unlike the nuclear genome, the mitochondrial genome of the Neanderthal from Hohlenstein-Stadel Cave in Germany is quite different from that of later Neanderthals—a previous report showed that more than 70 mutations distinguish it from the mitochondrial genomes of other Neanderthals. The researchers suggest that early European Neanderthals may have inherited DNA from a yet undescribed population.

As with what is going on in human fossil research in China, it seems as though there is a tangled web of relationships between human populations extending through both time and space.  Whatever complexity we envision for these groups, it is probably far more so.  As I wrote about the Chinese material:

The implications of these skulls are stark: there has been widespread population mixing and regional continuity in Europe and Asia for at least 400 thousand years. Not only did the Neandertals feel enough cultural kinship to mate and have children with these East Asian people, the early modern humans coming out of Africa did, as well.  As Chris Davis of China Daily News put it: “One big happy family.”

It is becoming increasingly clear that our simplistic notions of population replacement and regional continuity are probably wrong. Is evolution occurring in these human groups? It absolutely is. Just how these puzzle pieces relate to each other is the question.