Washington: Researchers have been able to determine an almost complete mitochondrial genome sequence of a 400,000-year-old hominin from Sima de los Huesos, a unique cave site in Northern Spain.
The researchers found that it is related to the mitochondrial genome of Denisovans, extinct relatives of Neanderthals in Asia.
Sima de los Huesos, the "bone pit", is a cave site in Northern Spain that has yielded the world`s largest assembly of Middle Pleistocene hominin fossils, consisting of at least 28 skeletons.
Matthias Meyer and his team from the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, collaborated with paleontologist Juan-Luis Arsuaga and applied new techniques to a cave bear from the Sima de los Huesos site.
After this success, the researchers sampled two grams of bone powder from a hominin thigh bone from the cave. They extracted its DNA and sequenced the genome of the mitochondria or mtDNA, a small part of the genome that is passed down along the maternal line and occurs in many copies per cell.
The researchers then compared this ancient mitochondrial DNA with Neandertals, Denisovans, present-day humans, and apes.
From the missing mutations in the old DNA sequences the researchers calculated that the Sima hominin lived about 400,000 years ago. They also found that it shared a common ancestor with the Denisovans, an extinct archaic group from Asia related to the Neandertals, about 700,000 years ago.
Matthias Meyer said that the fact that the mtDNA of the Sima de los Huesos hominin shares a common ancestor with Denisovan rather than Neandertal mtDNAs is unexpected since its skeletal remains carry Neandertal-derived features.
Considering their age and Neandertal-like features, the Sima hominins were likely related to the population ancestral to both Neandertals and Denisovans. Another possibility is that gene flow from yet another group of hominins brought the Denisova-like mtDNA into the Sima hominins or their ancestors.