Tag Archives: human evolution

Research establishes traces of Neandertal DNA present in genome of modern humans

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Research has established that there are traces of Neandertal DNA in the genome of modern humans. Now an exploratory study that assessed the facial structure of prehistoric skulls is offering new insights, and supports the hypothesis that much of this interbreeding took place in the Near East – the region ranging from North Africa to Iraq.

“Ancient DNA caused a revolution in how we think about human evolution,” says Steven Churchill, co-author of the study and a professor of evolutionary anthropology at Duke University. “We often think of evolution as branches on a tree, and researchers have spent a lot of time trying to trace back the path that led to us, Homo sapiens. But we’re now beginning to understand that it isn’t a tree – it’s more like a series of streams that converge and diverge at multiple points.”

“Our work here gives us a deeper understanding of where those streams came together,” says Ann Ross, corresponding author of the study and a professor of biological sciences at North Carolina State University.

Neanderthal

Neanderthal/Photo:en.wikipedia.org

“The picture is really complicated,” Churchill says. “We know there was interbreeding. Modern Asian populations seem to have more Neandertal DNA than modern European populations, which is weird – because Neandertals lived in what is now Europe. That has suggested that Neandertals interbred with what are now modern humans as our prehistoric ancestors left Africa, but before spreading to Asia. Our goal with this study was to see what additional light we could shed on this by assessing the facial structure of prehistoric humans and Neandertals.”

“By evaluating facial morphology, we can trace how populations moved and interacted over time,” Ross explains. “And the evidence shows us that the Near East was an important crossroads, both geographically and in the context of human evolution.”

For this study, the researchers collected data on craniofacial morphology from the published literature. This ultimately resulted in a data set including 13 Neandertals, 233 prehistoric Homo sapiens, and 83 modern humans.

The researchers focused on standard craniofacial measurements, which are reproducible, and used those measurements to assess the size and shape of key facial structures. This then allowed the researchers to do an in-depth analysis to determine whether a given human population was likely to have interbred with Neandertal populations, as well as the extent of that likely interbreeding.

“Neandertals had big faces,” Churchill says. “But size alone doesn’t establish any genetic link between a human population and Neandertal populations. Our work here involved a more robust analysis of the facial structures.”

The researchers also accounted for environmental variables that are associated with changes in human facial characteristics, to determine the likelihood that connections they established between Neandertal and human populations were the result of interbreeding rather than other factors.

“We found that the facial characteristics we focused on were not strongly influenced by climate, which made it easier to identify likely genetic influences,” Ross says. “We also found that facial shape was a more useful variable for tracking the influence of Neandertal interbreeding in human populations over time. Neandertals were just bigger than humans. Over time, the size of human faces became smaller, generations after they had bred with Neandertals. But the actual shape of some facial features retained evidence of interbreeding with Neandertals.”

“This was an exploratory study,” Churchill says. “And, honestly, I wasn’t sure this approach would actually work – we have a relatively small sample size, and we didn’t have as much data on facial structures as we would have liked. But, ultimately, the results we got are really compelling.

“To build on this, we’d like to incorporate measurements from more human populations, such as the Natufians, who lived more than 11,000 years ago on the Mediterranean in what is now Israel, Jordan and Syria.”

China archeo-tools suggest Man left Africa earlier than previously thought

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Ancient tools and bones discovered in Shangchen in the southern Chinese Loess Plateau by archaeologists suggest early humans left Africa and arrived in Asia earlier than previously thought.

The artefacts show that our earliest human ancestors colonised East Asia over two million years ago. They were found by a Chinese team that was led by Professor Zhaoyu Zhu of the Chinese Academy of Sciences, and included Professor Robin Dennell of Exeter University.

The tools were discovered at a locality called Shangchen in the southern Chinese Loess Plateau. The oldest are ca. 2.12 million years old, and are c. 270,000 years older than the 1.85 million year old skeletal remains and stone tools from Dmanisi, Georgia, which were previously the earliest evidence of humanity outside Africa.

The artefacts include a notch, scrapers, cobble, hammer stones and pointed pieces. All show signs of use – the stone had been intentionally flaked. Most were made of quartzite and quartz that probably came from the foothills of the Qinling Mountains 5 to 10 km to the south of the site, and the streams flowing from them. Fragments of animal bones 2.12 million years old were also found.

The Chinese Loess Plateau covers about 270,000 square kilometres, and during the past 2.6m years between 100 and 300m of wind-blown dust – known as loess – has been deposited in the area.  “Our discovery means it is necessary now to reconsider the timing of when early humans left Africa,” said Professor Dennell.

The 80 stone artefacts were found predominantly in 11 different layers of fossil soils which developed in a warm and wet climate. A further 16 items were found in six layers of loess that developed under colder and drier conditions. These 17 different layers of loess and fossil soils were formed during a period spanning almost a million years. This shows that early types of humans occupied the Chinese Loess Plateau under different climatic conditions between 1.2 and 2.12 million years ago.

The layers containing these stone tools were dated by linking the magnetic properties of the layers to known and dated changes in the earth’s magnetic field.

 

Human evolution was uneven, punctuated, due to Neanderthals?

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Neanderthals survived at least 3,000 years longer than we thought in Southern Iberia – what is now Spain – long after they had died out everywhere else, according to new research published in Heliyon.

The authors of the study, an international team from Portuguese, Spanish, Catalonian, German, Austrian and Italian research institutions, say their findings suggest that the process of modern human populations absorbing Neanderthal populations through interbreeding was not a regular, gradual wave-of-advance but a “stop-and-go, punctuated, geographically uneven history.”

Over more than ten years of fieldwork, the researchers excavated three new sites in southern Spain, where they discovered evidence of distinctly Neanderthal materials dating until 37,000 years ago.

“Technology from the Middle Paleolithic in Europe is exclusively associated with the Neanderthals,” said Dr. João Zilhão, from the University of Barcelona and lead author of the study. “In three new excavation sites, we found Neanderthal artefacts dated to thousands of years later than anywhere else in Western Europe. Even in the adjacent regions of northern Spain and southern France the latest Neanderthal sites are all significantly older.”

The Middle Paleolithic was a part of the Stone Age, and it spanned from 300,000 to 30,000 years ago. It is widely acknowledged that during this time, anatomically modern humans started to move out of Africa and assimilate coeval Eurasian populations, including Neanderthals, through interbreeding.

According to the new research, this process was not a straightforward, smooth one – instead, it seems to have been punctuated, with different evolutionary patterns in different geographical regions.

In 2010, the team published evidence from the site of Cueva Antón in Spain that provided unambiguous evidence for symbolism among Neanderthals. Putting that evidence in context and using the latest radiometric techniques to date the site, the researchers show Cueva Antón is the most recent known Neanderthal site.

“We believe that the stop-and-go, punctuated, uneven mechanism we propose must have been the rule in human evolution, which helps explaining why Paleolithic material culture tends to form patterns of geographically extensive similarity while Paleolithic genomes tend to show complex ancestry patchworks,” commented Dr. Zilhão.

The key to understanding this pattern, says Dr. Zilhão, lies in discovering and analyzing new sites, not in revisiting old ones. Although finding and excavating new sites with the latest techniques is time-consuming, he believes it is the approach that pays off.

“There is still a lot we do not know about human evolution and, especially, about the Neanderthals,” said Dr. Zilhão. “Our textbook ideas about Neanderthals and modern humans have been mostly derived from finds in France, Germany and Central Europe, but during the Ice Ages these were peripheral areas: probably as much as half of the Paleolithic people who ever lived in Europe were Iberians. Ongoing research has begun to bear fruit, and I have no doubt that there is more to come.”