Neanderthals Did Not Interbreed with Humans, Scientists Find

Genetic scientists change their minds again, after earlier announcing that Europeans interbred with Europeans.  Now it seems there was no interbreeding at all, as outlined in a new study from Cambridge university.

From The Telegraph: The genetic traits between humans and Neanderthals are more likely from a shared ancestry rather than interbreeding, a British study has suggested.

Cambridge University researchers concluded that the DNA similarities were unlikely to be the result of human-Neanderthal sex during their 15,000-year coexistence in Europe.

People living outside Africa share as much as four per cent of their DNA with Neanderthals, a cave-dwelling species with muscular short arms and legs and a brain slightly larger than ours.

The Cambridge researchers examined demographic patterns suggesting that humans were far from intimate with the species they displaced in Europe almost 40,000 years ago.

The study into the genomes of the two species, found a common ancestor 500,000 years ago would be enough to account for the shared DNA.

Their analysis, published in the journal Proceedings of the National Academy of Sciences (PNAS), contradicts recent studies that found inter-species mating, known as hybridisation, probably occurred.

Dr Andrea Manica, who led the study, said: "To me the interbreeding question is not whether there was hybridisation but whether there was any hybridisation that affected the subsequent evolution of humans. I think this is very, very unlikely.

"Our work shows clearly the patterns currently seen in the Neanderthal genome are not exceptional, and are in line with our expectations of what we would see without hybridisation.

"So, if any hybridisation happened then it would have been minimal and much less than what people are claiming now."

Evidence has shown that Neanderthals were driven into extinction by humans who were more efficient at finding food and multiplied at a faster rate.

A previous study in 2010 suggested that interspecies liaisons near the Middle East resulted in Neanderthal genes first entering humans 70,000 years ago.

Modern non-Africans share more with Neanderthals than Africans, supporting the claim that the mixing occurred when the first early humans left Africa to populate Europe and Asia.

The existence of a 500,000-year-old shared ancestor that predates the origin of Neanderthals provides a better explanation for the genetic mix.

Diversity within this ancestral species meant that northern Africans were more genetically similar to their European counterparts than southern Africans through geographic proximity.

This likeness persisted over time to account for the overlap with the Neanderthal genome we see in modern people today.

Differences between populations can be explained by common ancestry, Dr Manica said.

"The idea is that our African ancestors would not have been a homogeneous, well-mixed population but made of several populations in Africa with some level of differentiation, in the way right now you can tell a northern and southern European from their looks," she said.

“Based on common ancestry and geographic differences among populations within each continent, we would predict out of Africa populations to be more similar to Neanderthals than their African counterparts – exactly the patterns that were observed when the Neanderthal genome was sequenced, but this pattern was attributed to hybridisation.

"Hopefully, everyone will become more cautious before invoking hybridisation, and start taking into account that ancient populations differed from each other probably as much as modern populations do.”

Northern Africans would be more similar to Europeans and ancient similarity stayed because there wasn't enough mixing between northern and southern Africans.

Population diversity, known as substructure, cant explain data on the shared genes, said David Reich, a professor of genetics at Harvard Medical School, in Boston who authored the 2010 study.

We have ruled out the possibility that ancient substructure can explain all the evidence of greater relatedness of Neanderthals to non-Africans than to Africans, he added.

Dr Manica said hybridisation between Neanderthals and humans can never be disproved entirely. 

Oldest “Modern Human” DNA Extracted from “Caveman” Bones in Spain—Linked to Northern European populations

Scientists have extracted DNA from 7,000 year old “caveman” bones found in Spain and genetically matched them to modern northern European populations.

Previously, the oldest modern human genomes yet recovered yet came from Ötzi the Iceman, a 5,300-year-old mummy found in the Alps in 1991. 

Researchers have salvaged DNA from even older human cells, but this comes from the mitochondria that generate energy for our bodies, and not from the nucleus where our chromosomes are housed. (Mitochondrial DNA is passed down only by mothers.)

Now researchers have rescued fragments of genomes from the remains of two cavemen unearthed in northern Spain.

"These are the oldest partial genomes from modern human prehistory," researcher Carles Lalueza-Fox, a paleogeneticist at the Spanish National Research Council, was quoted as saying.

The skeletons of two young adult males were discovered by chance in 2006 by cave explorers in a cavern high in the Cantabrian mountain range, whose main entrance is found at 4,920 feet (1,500 meters) altitude. Winters there are notably cold, which helped preserve the DNA in the bones.

These bones date back to the Mesolithic period, before agriculture spread to the Iberian Peninsula with Neolithic settlers from the Middle East. These cavemen were hunter-gatherers, judging by the ornament that one was found with of red-deer canines embroidered onto a cloth.

The scientists recovered 1.34 percent and 0.5 percent of the human genomes from the bones of these two cave men. Analyses revealed that current populations of the Iberian Peninsula, which includes Spain, Portugal and Andorra, are not genetically linked with these ancient hunter-gatherers. Instead, these cavemen were closer genetically to the current populations of northern Europe.

"There are many works that claim the Basques [of the Iberian Peninsula] could be descendants from Mesolithics that became isolated in the Basque country," Lalueza-Fox said. "We found the modern Basques are genetically not related to these two individuals."

The scientists also recovered the complete mitochondrial DNA of one of these cavemen. This revealed that European populations during the Mesolithic were very uniform genetically.

"Despite their geographical distance, individuals from the regions corresponding to the current England, Germany, Lithuania, Poland and Spain shared the same mitochondrial lineage," Lalueza-Fox said. "These hunters-gatherers shared nomadic habits and had a common origin."

The researchers now aim to complete the genomes of both cavemen. Such data could help "explore genes that have been modified with the arrival of the Neolithic in the European populations," Lalueza-Fox said.

New Study of Hallstatt Skulls Sparks Evolutionary Debate

A new study of the famous “Hallstatt skulls” has raised renewed questions about evolutionary change, according to Evolution magazine.

Quoting a study completed by researchers at the Universities of Manchester and Barcelona, the magazine reported that the evidence indicated that “the human skull is highly integrated, meaning variation in one part of the skull is linked to changes throughout the skull.”

The researchers examined 390 skulls from the Austrian town of Hallstatt, part of a famous collection kept in the local Catholic Church ossuary. A somewhat bizarre local tradition has developed there that the remains of the town's buried dead are exhumed to make space for more recent burials.

The skulls are also decorated with paintings and, crucially, bear the name of the deceased.

The Barcelona team made measurements of the skulls and collected genealogical data from the church's records of births, marriages and deaths, allowing them to investigate the inheritance of skull shape.

The team tested whether certain parts of the skull – the face, the cranial base and the skull vault or brain case – changed independently, as anthropologists have always believed, or were in some way linked.

The scientists simulated the shift of the foramen magnum (where the spinal cord enters the skull) associated with upright walking; the retraction of the face, thought to be linked to language development and perhaps chewing; and the expansion and rounding of the top of the skull, associated with brain expansion.

They found that, rather than being separate evolutionary events, changes in one part of the brain would facilitate and even drive changes in the other parts.

"We found that genetic variation in the skull is highly integrated, so if selection were to favour a shape change in a particular part of the skull, there would be a response involving changes throughout the skull," Dr Chris Klingenberg, from Manchester's Faculty of Life Sciences was quoted as saying.

“We were able to use the genetic information to simulate what would happen if selection were to favour particular shape changes in the skull. As those changes, we used the key features that are derived in humans, by comparison with our ancestors: the shift of the foramen magnum associated with the transition to bipedal posture, the retraction of the face, the flexion of the cranial base, and, finally, the expansion of the braincase.

"As much as possible, we simulated each of these changes as a localised shape change limited to a small region of the skull. For each of the simulations, we obtained a predicted response that included not only the change we selected for, but also all the others. All those features of the skull tended to change as a whole package.

“This means that, in evolutionary history, any of the changes may have facilitated the evolution of the others."

Lead author Dr Neus Martínez-Abadías, from the University of Barcelona, added: "This study has important implications for inferences on human evolution and suggests the need for a reinterpretation of the evolutionary scenarios of the skull in modern humans."

Source: Martínez-Abadías, N.; Esparza, M.; Sjövold, T.; González-José,

R.; Santos, M.; Hernàndez, M.; Klingenberg,C.P. "Pervasive genetic integration directs the evolution of human skullshape". Evolution, November 2011.