The truth is that little is known about our unique genetic makeup as distinguished from our archaic cousins, and how it contributed to the fact that we are the only species among them to survive. Even less is known about our unique epigenetic makeup, but it is exactly such epigenetic changes that may have shaped our own species.
While genetics deals with the DNA sequence itself and the heritable changes in the DNA (mutations), epigenetics deals with heritable traits that are not caused by mutations. Rather, chemical modifications to the DNA can efficiently turn genes on and off without changing the sequence. This epigenetic regulatory layer controls where, when and how genes are activated, and is believed to be behind many of the differences between human groups.
Indeed, many epigenetic changes distinguish us from the Neanderthal and the Denisovan, researchers at the Hebrew University of Jerusalem and Europe have now shown.
In an article just published in Science, Dr. Liran Carmel, Prof. Eran Meshorer and David Gokhman of the Alexander Silberman Institute of Life sciences at the Hebrew University, along with scientists from Germany and Spain, have reconstructed, for the first time, the epigenome of the Neanderthal and the Denisovan. Then, by comparing this ancient epigenome with that of modern humans, they identified genes whose activity had changed only in our own species during our most recent evolution.
Among those genetic pattern changes, many are expressed in brain development. Numerous changes were also observed in the immune and cardiovascular systems, whereas the digestive system remained relatively unchanged.
On the negative side, the researchers found that many of the genes whose activity is unique to modern humans are linked to diseases like Alzheimer’s disease, autism and schizophrenia, suggesting that these recent changes in our brain may underlie some of the psychiatric disorders that are so common in humans today.
By reconstructing how genes were regulated in the Neanderthal and the Denisovan, the researchers provide the first insight into the evolution of gene regulation along the human lineage and open a window to a new field that allows the studying of gene regulation in species that went extinct hundreds of thousands of years ago.
Header Image : WikiPedia
Contributing Source : Hebrew University of Jerusalem
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The first ancestors of today’s non-African peoples probably took a southern route through the Arabian Peninsula as early as 130,000 years ago, the researchers found. The study is published by Professor Katerina Harvati and her team from the Institute for Archaeological Sciences at the University of Tübingen and the Senckenberg Center for Human Evolution and Palaeoenvironment, in collaboration with colleagues from the University of Ferrara, Italy, and the National Museum of Natural History, France. The study appears in the online Early Edition of the Proceedings of the National Academy of Sciences.
The scientists tested different hypothetical dispersal scenarios, taking into account the geography of potential migration routes, genetic data and cranial comparisons. They found that the first wave of migration out of Africa started earlier than previously thought, taking place as early as the late Middle Pleistocene – with a second dispersal to northern Eurasia following about 50,000 years ago.
Most scientists agree that all humans living today are descended from a common ancestor population which existed 100,000 to 200,000 years ago in Africa. The decreasing genetic and phenotypic diversity observed in humans at increasing distances from Sub-Saharan Africa has often been interpreted as evidence of a single dispersal 50,000 to 75,000 years ago. However, recent genetic, archaeological and palaeoanthropological studies challenge this scenario.
Professor Harvati’s team tested the competing out-of-Africa models of a single dispersal against multiple dispersals of anatomically modern humans. The scientists compared modern human crania from different parts of the world, neutral genetic data, and geographical distances associated with different dispersal routes. Likewise, they reconstructed population split times from both the genetic data and as predicted by each competing model. Because each dispersal scenario is associated with specific geographic and temporal predictions, the researchers were able to test them against the observed neutral biological distances between groups, as revealed from both genetic and cranial data.
“Both lines of evidence – anatomical cranial comparisons as well as genetic data – support a multiple dispersal model,” says Katerina Harvati. The first group of our ancestors left Africa about 130,000 years ago and followed a coastal route through the Arabian Peninsula to Australia and the west Pacific region. “Australian aborigines, Papuans and Melanesians were relatively isolated after the early dispersal along the southern route,” says Hugo Reyes-Centeno, first author of the study and member of the Tübingen team. He adds that other Asian populations appear to be descended from members of a later migratory movement from Africa to northern Eurasia about 50,000 years ago.
The researchers are confident that continued field work and advances in genetics will allow for fine-tuning of models of human expansion out of Africa. So far we can only speculate whether, for example, severe droughts in East Africa occurring between 135,000 and 75,000 years ago prompted migration or had an impact on the local evolution of human populations. The southern route region is a vast geographical space that has been understudied by archaeologists and anthropologists, so future work in this area will help support their findings.
Header Image : Landmarks of the temporal bone shown in one individual. The temporal bone has been shown to reflect modern human population history better than other parts of the cranium. It was therefore used in this study to infer migration patterns, in addition to genetic data. Shown here is the mean temporal bone shape of all individuals in the study. Figure: Katerina Harvati/University of Tübingen and Senckenberg Center for Human Evolution and Palaeoenvironment
Contributing Source : Universitaet Tübingen
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