By Dr Irengbam Mohendra Singh
While God has been elusive for eternity, refusing to unfold his mysteries, if we look back in time we will find that we have begun to unravel the mysteries of nature with vast changes in our intellectual achievements, such as Gödel’s theorem, molecular biology and Wittgenstein’s antiphilosophy.
In the midst of all these, archaeologists and geneticists were flabbergasted at the discovery of a new human cousin. Professor Chris Stringer, human origins researcher at London’s Natural History Museum, one of the leading proponents of the recent single (African) origin hypothesis, remarked that: “This new DNA work provides an entirely new way of looking at the evolution of humans in central and eastern Asia.”
The plot is thickening about the origin of early humans who inhabited this planet of ours. There may have been seven distinct types of human ancestor from Africa who expanded to remote islands of Indonesia, Europe and Siberia.
Every one of them became extinct like the dinosaurs between thousands of years to millennia except us. It may have been because of the ingenuity, intelligence and adaptability of the Homo sapiens species that we are here today. Our brain has now reached maturity and it will not expand any more. And we are here to stay.
The surprise story began in March 2010 when scientists, led by Johannes Krause and fellow researcher, Swedish biologist Svante Paabo from Mark Planck Institute for Evolutionary Anthropology in Leipzig, Eastern Germany, published online in the “Nature”, the finding of the DNA from a girl’s old finger bone.
The bit of bone but a huge bone for evolutionists was found in 2008 by Russian archaeologists from the Institute of Archaeology and Ethnology of Novosibirsk, working at the site of Denisova cave, in the Altai Krai Mountains of southern Siberia. They sent it to Leipzig for identification
A finger bone fragment from the fifth finger of a juvenile female that lived 40,000 years ago, as well as a fragment of a molar tooth, much bigger than human molar was discovered. The finger bone was found within 65 miles of known Neanderthal and modern human sites. Later in 2011, a toe bone was also unravelled (it is currently undergoing analysis).
The finger bone’s mitochondrial DNA (mtDNA) analysis showed it to be distinct from the mtDNAs of Neanderthals and modern humans. Subsequent studies on the nuclear genome from this specimen, as well as mtDNA from the tooth, determined that this group shares a common origin with Neanderthals and interbred with the ancestors of some present day Melanesians (people from the islands of Papa New Guinea) and Australian aborigines.
This juvenile hominin is now dubbed the “X-woman” (referring to the maternal descent of mtDNA), or the “Denisova hominin”. Some artefacts, including a bracelet, excavated in the cave at the same level were carbon dated to around 40,000 BP.
Prof Paabo noted that the existence of these distant branch humans creates much more complex picture of human kind during the late Pleistocene epoch. Denisova Cave is known to have also been inhabited by Neanderthal people and perhaps by modern humans. Because of the cool climate in this location, the discovery benefited from DNA’s ability to survive for longer periods at lower temperatures of the cave at 32 degrees Fahrenheight.
The analysis indicated that modern humans, Neanderthals and the Denisova hominin last shared a common ancestor around 1 million years ago. Denisovans are found to be a sister group to Neanderthals and had similar ancestors, because all non-African humans have Neanderthal DNA.
According to researchers, this provides confirmation that there were at least four distinct types of humans in existence (including Homo erectus) when anatomically modern humans (Homo sapiens) first left their African homeland.
The fact that Denisovans were discovered in southern Siberia, but contributed genetic material to modern human populations in Southeast Asia suggests that their population may have been widespread in Asia during the Pleistocene age.
The DNA analysis further indicated that these new Denisovans were the result of an earlier migration out of Africa, distinct from the later out-of-Africa migrations associated with Neanderthals and modern humans, but also distinct from the earlier migration of Homo erectus, who were to colonise Asia.
According to the co-author in the “Nature”, Richard Green of the University of California, Santa Cruz, there was probably an ancestral group that left Africa between 300,000 and 400.000 years ago and quickly diverged, with one branch becoming the Neanderthals who spread into Europe and the other branch moving east and becoming Denisovans.
When modern humans left Africa 60,000 years ago, they first encountered the Neanderthals, an interaction prevailed that left traces of Neanderthal DNA scattered throughout the genomes of all non-Africans. The other group of humans later came in contact with Denisovans leaving traces of Denisovan DNA in the genomes who settled in Melanesi – an assemblage of islands of Australia’s coast including New Guinea.
Richard Green says, “It was fruitous that this discovery came quickly on the heels of the Neanderthal genome, because we already had the team ready to do a similar analysis.” He said Denisovans were quite different from Neanderthals and modern humans. They had teeth similar to those of older human ancestors, such as Homo erectus.
The Leipzig scientist Kraus said that since the discovery was announced in March 2010, the researchers have been focussed on the task of decoding the entire 3 billion DNA building blocks in the complete genetic make-up of the newcomer from the Atlai Mountains.
The Leipzig scientists have also reported the isolation and sequencing of nuclear DNA from the Denisovan finger bone in 2010. The specimen showed an unusual preservation of DNA and low level of contamination, allowing them a detailed comparison of its genome with Neanderthal and modern humans.
They concluded that the Denisovan population along with Neanderthal shared a common branch from the lineage leading to modern African humans.. The estimated average time of divergence between Denisovans and Neanderthals sequences is 640,000 years ago, and between both of these and the sequences of modern Africans is 804,000 years ago.
Modern genetic studies show that app. 4% of non-African modern human DNA relates to Neanderthals. A new comparison of Denisovan genome from six modern humans, one each from South Africa, Nigeria, France, Hans Chinese, Papua New Guinea and Bougainville islands showed that between 4% and 6% of the genome of the Melanesians derive from Denisovan population.
The scientists suggest that the genes were probably introduced during the early migration of the ancestors of Melanesians into Southeast Asia, where Denisovans once ranged widely over eastern Asia.
Mark Stoneking, molecular anthropologist at the Max Planck Institute for Evolutionary anthropology, Leipzig, (most famous for his estimation that human clothing originated about 72,000 years ago, by sequencing the genes of head and body lice in 2007) led a research team, which found genetic evidence that, in addition to Melanesians, Australian aborigines, and small, scattered groups of people in Southeast Asia, such as Negrito of Mamanawa in the Phillipines shares Denisovan ancestry, though Andaman Islander Negritos and Malaysian Jehai, do not.
With their result, they challenged the belief that Denisovans interbred in mainland Asia before spreading to the island from Southeast Asia, Melanesia, and Australia.
Recent genetic studies in 2011 have indicated that modern humans may have mated with “at least two groups” of ancient humans: Neanderthals and Denisovans.
Ian Tatersall of the Department of Physical Anthropology at the American Museum of National History says that “We are the only hominid around today, and we tend to think that that’s how it’s always been. But the evidence is accumulating that the human evolutionary tree is quite luxuriantly branching.
Scientists have no idea what the Denisovan hominis look like. Paabo says that because the Denisova homini is assumed to be human, it’s possible that there are many unknown homini fossils waiting to be discovered. Palaeontologists will continue to scour for remnants in Siberia.
Apart from Denisovans, scientists discovered a new very strange humanlike species (published in “Nature” in 2004) that lived over the past few hundred years in the east of the last islands of Java in Indonesia – a scattered remote archipelago. The remains of this new species had been excavated in 2004, in Liang Bua Cave on the island of Flores, and hence named Homo floresiensis (aka the Hobbit). The creature was only one meter tall and very small-brained.
Homo floresiensis was considered intelligent as the cave contained evidence of tool making, butchery of animal carcasses, and fire. They survived until about 17,000 years ago. The latest studies of the Hobbit bones have led to the radical idea that these tiny people in fact, descended from something more primitive than Homo erectus – yet another species whose ancestors emerged from Africa 2 million years ago, or more, and then evolved in isolation in Southeast Asia, finally disappearing within the last 20 millennia.
There is no knowledge of when the Neanderthals ad Homo erectus disappeared, overwhelmed by Homo sapiens, probably because of better tools and other resources.
What stumps the scientists by the finding this strange humanlike creatures is that Africa could have been home to yet another species of humans within the last 50,000 years, based on signs of possible ancestral DNA in modern African populations and fossils found in Nigeria and Congo.
The writer is based in the UK
Published: March 6, 2012