Modern Human Ancestors Mated With Neanderthals - New Genetic Evidence

in biology, omics

There have been several past reports suggesting interbreeding between modern humans and the Neanderthals. A new study further confirms that Neanderthals and expanding African migrants mated prior to or very early on the way out of Africa leading to the successful colonization of the planet.

The Neanderthals were a human group, an extinct member of the ancient humans.  They appeared around 130,000 years ago and disappeared in Asia by 50,000 and in Europe by about 30,000 years ago. Evidences indicate that Homo sapiens and Neanderthals evolved from a chimp-like ancestor between five and 10 million years ago.

The study was published in the recent issue of the scholarly journal Molecular Biology and Evolution. The lead author of the study was Dr Damian Labuda.
 

Homo sapiens neanderthalensis

Homo neanderthalensis. Skull discovered in 1908 at
La Chapelle-aux-Saints (France). Source: Wikipedia

The current study reports that some of the human X chromosome originates from Neanderthals and is found exclusively in people outside Africa.  Humans have 23 pairs of chromosomes, one pair being sex chromosomes.  Sex chromosomes in the female are named X and X, and that in the male, X and Y. 

Dr. Labuda and his team almost a decade ago had identified a piece of DNA (called a haplotype) in the human X chromosome that seemed different and whose origins they questioned. When the Neanderthal genome was sequenced in 2010, they quickly compared 6000 chromosomes from all parts of the world to the Neanderthal haplotype.

The Neanderthal sequence was present in peoples across all continents, except for sub-Saharan Africa, and including Australia.

“There is little doubt that this haplotype is present because of mating with our ancestors and Neanderthals. This is a very nice result, and further analysis may help determine more details,” says Dr. Nick Patterson, of the Broad Institute of MIT and Harvard University, a major researcher in human ancestry who was not involved in this study.

Neanderthals, whose ancestors left Africa about 400,000 to 800,000 years ago, evolved in what is now mainly France, Spain, Germany and Russia, and are thought to have lived until about 30,000 years ago. Meanwhile, early modern humans left Africa about 80,000 to 50,000 years ago. The question on everyone's mind has always been whether the physically stronger Neanderthals, who possessed the gene for language and may have played the flute, were a separate species or could have interbred with modern humans. The answer is yes, the two lived in close association.

“In addition, because our methods were totally independent of Neanderthal material, we can also conclude that previous results were not influenced by contaminating artifacts,” adds Dr. Labuda. They analyzed an X-linked haplotype present in an 8-Kb intron spanning exon 44 of the dystrophin gene. This was referred to as dys44. Introns are non-coding sequences interspersed between exons, which are sequences that code for genetic messages.

Previous studies that analyzed the mitochondrial DNA have not provided conclusive evidence of Neanderthal maternal contribution to modern humans.  Mitochondrial DNA is mostly transferred from the mother to the offspring.

“Dr. Labuda and his colleagues were the first to identify a genetic variation in non-Africans that was likely to have come from an archaic population. This was done entirely without the Neanderthal genome sequence, but in light of the Neanderthal sequence, it is now clear that they were absolutely right!” adds Dr. David Reich, a Harvard Medical School geneticist, one of the principal researchers in the Neanderthal genome project.

So, speculates Dr. Labuda, did these exchanges contribute to our success across the world? “Variability is very important for long-term survival of a species,” says Dr. Labuda. “Every addition to the genome can be enriching.” An interesting match, indeed.

Source article: An X-linked haplotype of the Neandertal origin is present among all non-African populations.  Vania Yotova, Jean-Francois Lefebvre, Claudia Moreau, Elias Gbeha, Kristine Hovhannesyan, Stephane Bourgeois, Sandra Be´darida, Luisa Azevedo, Antonio Amorim, Tamara Sarkisian, Patrice Hodonou Avogbe, Nicodeme Chabi, Mamoudou Hama Dicko, Emile Sabiba Kou' Santa Amouzou, Ambaliou Sanni, June Roberts-Thomson, Barry Boettcher, Rodney J. Scott, and Damian Labuda.Molecular Biology and Evolution. (2011)  doi: 10.1093/molbev/msr024.

Other references used: 1. Neandertal Genome: The Ins and Outs of African Genetic Diversity. Hodgson JA, Bergey CM and Disotell TR. Current Biology. (2010) 20:R517. DOI: 10.1016/j.cub.2010.05.033.
2. Wikipedia  

 

 

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