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Skull Collection Helps Explain Early Neanderthal Evolution

An examination of 17 ancient skulls shows that some Neanderthal features arose as far back as 430,000 years ago.

By | June 19, 2014

Skull from Sima de los HuesosJAVIER TRUEBA/MADRID SCIENTIFIC FILMSThe separation of the Neanderthal and modern human lineages was thought to have occurred during the Middle Pleistocene era (from 780,000 to 130,000 years ago), but exactly when and how this separation occurred is still unclear. Now, an analysis of 17 ancient skulls from a site in Atapuerca, Spain, provides evidence of the early evolution of the Neanderthal lineage. The results were published today (June 19) in Science.

Juan Luis Arsuaga Ferreras, a professor of human paleontology at Complutense University of Madrid in Spain, along with his colleagues characterized this unique collection of specimens from a small chamber within a cave called Sima de los Huesos, finding that the skulls show a combination of both Neanderthal and more ancient morphologies.

The researchers estimate that the skulls are about 430,000 years old—the oldest specimens with Neanderthal features to be found thus far, according to Arsuaga.

“We now have a reliable minimum age for the split between the lineages that ultimately led to the Neanderthals and to the modern humans,” said coauthor Warren Sharp from the Berkeley Geochronology Center in California. “We know that the Sima fossils are already part way down the branch that led to the Neanderthal, so the common ancestor of the Neanderthals and Homo sapiens must be older than 430,000 years.”

“Until recently, most [scientists] supported [the idea] that Neanderthals emerged, at most, 250,000 years ago. The discovery at Sima demonstrates that there is a much deeper history of the Neanderthals than we previously thought, to at least 430,000 years ago,” said Jean-Jacques Hublin from the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, who was not involved in the work but penned a perspective article accompanying the study. “[These new specimens] are clearly not like the late Neanderthals, but ancestral forms of Neanderthals.”

Researchers have explored this excavation site for more 30 years, uncovering at least 28 different, but biologically similar, individuals—mostly young adults. “The material from Sima is absolutely unbelievable because of the large number of individuals represented by all parts of the skeleton,” said Hublin. The present study now provides details of the almost complete skulls of 17 of these individuals, including seven newly found specimens.

The fossils were previously dated to more than 530,000 years ago and were considered to be those of Homo heidelbergensis, an extinct ancient lineage ancestral that may be parental to both Neanderthals and modern Homo sapiens. But for the current study, the team used more modern dating technologies: uranium-series dating of carbonate directly in contact with one of the skulls and luminescence dating of a layer of mud on top of the specimens. “We have confirmation from these two distinct and quite independent dating techniques showing an age of about 430,000 years for these fossils,” said Sharp.

Studying the face, jaws, teeth, and craniums of these ancient individuals, the researchers found that all of the specimens had the same combination of features, including some typical of later Neanderthals. “The Atapuerca team confirm that the Sima skulls, jaws, and teeth show many Neanderthal features, including the shape of the brow ridges, occipital bone and face, and the patterns of cusps on the teeth,” Chris Stringer, an anthropologist at London’s Natural History Museum, told The Scientist in an e-mail. “[The evidence shows] that these fossils belong to the Neanderthal lineage but not to the Homo heidelbergensis species.”

But the craniums were smaller than those of later Neanderthals, making them closer to more primitive lineages and providing evidence for a gradual evolution pattern of the Neanderthal lineage, lending support to the so-called accretion model first proposed by Hublin.

Scientists continue to excavate early human bones from the cave in northern Spain. And similarity among the individual specimens will allow for a detailed analysis of sexual differences between the skeletons and of the development and growth of the individuals, said Arsuaga.

“The rich Sima de los Huesos material, with every part of the skeleton beautifully preserved, will continue to inform us about human evolution 400,000 years ago as research continues on this astonishing, and even beautiful, collection of human fossils,” said Stringer.

J.L. Arsuaga et al., “Neandertal roots: cranial and chronological evidence from Sima de los Huesos,” Science, doi:10.1126/science.1253958, 2014.

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Avatar of: James V. Kohl

James V. Kohl

Posts: 162

June 21, 2014

Population geneticists tend to observe "...separation of the Neanderthal and modern human lineages..." and report that it "...provides evidence of the early evolution of the Neanderthal lineage." Serious scientists understand that conserved molecular mechanisms enable nutrient-dependent pheromone-controlled cell type differentiation (via amino acid substitutions) that is manifested in morphological and behavioral phenotypes in species from microbes to man.

For example, dietary differences in nematodes led predatory P. pacificus to develop teeth and patterns of feeding differentiated their neuronal wiring and behavior from C. elegans, a nematode without teeth. The mandibles and penises of male crickets simultaneously adapted.

It's extremely unlikely that the nutrient-dependent amino acid substitutions that differentiate sex differences in cell types or other differences in the cell types of all individuals of all species would suddenly not be the cause of differences in Neandertals compared to modern human populations or compared to other primates. Dobzhansky (1973) noted, for example, that the "so-called alpha chains of hemoglobin have identical sequences of amino acids in man and the chimpanzee, but they differ in a single amino acid (out of 141) in the gorilla."

However, if you deny the logic of everything else Dobzhansky wrote (see for example Biology, molecular and organismic), it may be possible to continue believing that differences in jaws and teeth led to differences in evolutionary paths. I prefer to accept the fact that differences in diet and the metabolism of nutrients to species-specific pheromones that control the physiology of reproduction are responsible for ecological speciation.

I think that Dobzhansky might also accept that fact if he had lived long enough and continued to learn more about the cell type differentiation that some people still attribute to mutations and natural selection in the context of the evolution of biodiversity. In 1964, he seems to have called those people "bird watchers" and "butterfly collectors."

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