Recent discoveries of new human species
Denisovans
Sister group to Neanderthals, found 2001, 2010, Denisova Cave, Siberia; interbreeding with humans; genomes of New Guineans, Melanesian islanders, Australian 5% Denisovan; Negritos (Philippines) 2.5%.
Then, in 2010, DNA extracted from a tiny fragment of fossilised finger discovered by Russian archaeologists in Denisova Cave in southern Siberia in 2008 revealed that the owner was a member of a previously unknown group of ancient people who were neither Neanderthals nor modern humans. From nuclear DNA from the finger, scientists were able to work out a draft sequence of the full genetic code or genome of this young female who dies when she was 8 years old, and when they compared her genome with that of modern humans and Neanderthals, they discovered that some of her relatives may have interbred with the ancestors of Melanesians living today in Papua New Guinea, which suggested that the Denisovans may have been widespread in Asia in the past[1].
Also in 2010, two other fossils were found to contain DNA similar to the finger fragment, both of them molars. The first tooth was bigger than either a modern human or a Neanderthal tooth, in size and shape resembling the teeth of much more primitive members of the genus Homo who lived in Africa millions of years ago. The second molar, even larger than the first, was found in 2010 in the same cave chamber that had yielded the fragment of finger bone – indeed, near the bottom of the same 30,000 to 50,000 year old deposits. Only a small amount of DNA was able to be extracted from these teeth, but the finger fragment turned out to be exceptionally generous, yielding 70% endogenous DNA[2], its state of preservation being attributable to the coldness of the cave in which it had reposed for so many years.
Then, a further study of the owner’s well-preserved mitochondrial DNA[3], which is passed down from mother to child, resulted in the sequencing of the whole genome. Mitochondrial DNA has been described as a limited record of a population’s history, rather “like a single page torn from a book”, but the sequencing of both the Neanderthal and Denisovan genomes in this fashion has allowed many more pages of the book to be read. This revealed that human genomes today actually contain a small amount of the Neanderthal code – on average about 2.5%. It also showed that the Denisovans were a sister group to the Neanderthals, which suggests that some ancestral humans who left Africa between 300,000 and 400,000 years ago split into the Neanderthals and Denisovans.
When modern humans left Africa about 70,000 to 80,000 years ago, they encountered Neanderthals and, as we have seen, it is more than likely that some sexual liaisons occurred, most likely in the Middle East. About 1% to 4% of the genetic code of non-Africans[4] today comes from Neanderthals as a result. Later, it seems, one group of humans came across the Denisovans as well, a meeting that left traces of Denisovans in the people who eventually settled in Melanesia. On average, the genomes of New Guineans, people from islands in Melanesia and Australian aborigines are about 5% Denisovan. Negritos in the Philippines are about 2.5%. The big question is why no traces have been found in modern humans in areas between the original fossil find and Melanesia – in Russia or nearby China or anywhere else for the matter.
A plausible hypothesis as to what may have occurred is as follows:
“Sometime before 500,000 years ago, probably in Africa, the ancestors of modern humans split off from the lineages that would give rise to Neanderthals and Denisovans. (The most likely progenitor of all three types was ... Homo heidelbergensis). While our ancestors stayed in Africa, the common ancestor of Neanderthals and Denisovans migrated out. Those two lineages later diverged, with the Neanderthals initially moving west into Europe and the Denisovans moving east, perhaps initially populating large parts of the Asian continent.
“Later still, when modern humans ventured out of Africa themselves, they encountered Neanderthals in the Middle East and central Asia, and to a limited extent bred with them…. This mixing most likely occurred between 67,000 and 46,000 years ago. One population of modern humans then continued east into Southeast Asia, where, sometime around 40,000 years ago, they encountered Denisovans. The moderns interbred with them as well and then moved into Australasia, carrying Denisovan DNA.
“This scenario might explain why the only evidence so far that Denisovans even existed is three fossils from a cave in Siberia and a 5% stake in the genomes of people living today thousands of miles to the southeast. But it (still leaves) a lot of questions unanswered. If the Denisovans were so widespread, why was there no trace of them in the genomes of Han Chinese or of any other Asian people between Siberia and Melanesia?” Also why have they left no mark in the archaeological record – no distinctive tools, say, who were thy and what did they look like?[5]
Today, the reality is that the only way Denisovans can be known is by their DNA. Further refinements In DNA technique have resulted in a new version of the finger bone’s genome, one so precise that it waspossible to discriminate between genetic information inherited from the mother and that from the father. The result that there are now available two highly accurate Denisovan genomes, one from each parent. And all this from a single chip bone, greatly assisting in defining the changes which took place after we separated from our most recent ancestor. In the words of the leading member of the team who made these discoveries, the lasting contribution of studying Denisovan DNA “will be in finding what is exclusively human”[6].
Another remarkable feature of the Denisovan cave itself was that it contained both Neanderthal and Denisovan fossilised remains at the same level of activity (level 11, dated 30,000 to 50,000 years ago), and also signs of later human activity in the form of a beautiful bracelet of polished green stone. So the cave was an obvious source of attraction for all three species, probably because it provided a suitable refuge during the harsh Siberian winter.
Another Denisovan find [6.1]
More recently, further Denisovan remains have been identified in a fossilised chunk of the lower jaw of an adolescent including two teeth at least 160,000 years old, found in 1980 in the Baishiya Karst Cave in the Gansu province of China, roughly 2300 kilometres to the south-east of the Siberian cave discovery. No DNA could be found, but scientists recovered protein fragments that they compared to the Siberian DNA. That showed the fossil came from a Denisovan.
The find addresses several mysteries. One was why the Siberian DNA indicated Denisovans were adapted to living at high altitudes when the Siberian cave is relatively close to sea level. The Chinese cave, by contrast, is on the high-altitude Tibetan Plateau, about 3280 metres high, indicating a remarkable ability of the species to adapt to the inhospitable climate there. Previous research had indicated that Denisovans must have lived somewhere other than Siberia, because traces of their DNA can be found in several present-day populations of Asia and Australia whose ancestors probably didn't pass through that region. The new finding expands their known range. It would appear that Denisovans may have been distributed all across Asia.
Experts unconnected to the research agreed the fossil could help identify other remains as Denisovan, for example a fossil jaw reported in 2015 dredged by a fishing net off the coast of Taiwan. In addition to the anatomy, the study's approach of using protein from the bone or teeth could also be used on fossils to look for evidence of Denisovan identity.
Further fossil finds
The Red Deer Cave people, Red Deer Cave, Longlin Cave, S-W China, fl 14,500-11,500 yrs ago
More recently, fossils of a previously unknown group of prehistoric humans, who lived as recently as 11,000 years ago, have been discovered in south-west China. The fossils, dated between 14,500 and 11,500 years old, were found in Maludong, or Red Deer Cave, in Yunnan province and in Longlin Cave in Guanxi Zhuang autonomous region. They have been dubbed the Red Deer cave people. Their appearance is very different to all modern humans, whether alive today or in Africa 150,000 years ago. They had short flat faces with archaic features such as big teeth and thick skulls. A CT scan suggests that they had a moderate size brain with a moderate looking frontal lobe, but primitive looking parietal lobes on the side. They ate a lot of venison including a giant extinct red deer. It has been described as a species very close to but not quite us.
South-west China has been a focal point of much recent research because it is a ‘hotspot’ of human genetic diversity. It has been conjectured that it may well be an area where the very earliest humans from Africa settled before dispersing into other parts of Asia. We have seen that modern humans are thought to have evolved in Africa about 150,000 years ago and then left the Middle East to travel to Australia about 70,000 years ago. One possibility is that the Red Deer Cave people were descendants of a group of modern humans who made an even earlier exodus from Africa and settled in China before the ancestors of people living there today arrived. Or they could be a new species of human – a possibility not so radical given the surprising and recent discoveries of the two new human species in Asia – Homo floresiensis (the hobbit) in Indonesia [7] and the Denisovans.
Attempts to get genetic material from these Chinese remains have been unsuccessful. What is clear is that there was a lot of human diversity in this region about 20,000 years ago – the hobbit in Indonesia and the Red Deer Cave people in China.
Further fossil finds in the Guangxi (Guanxi) Zhuang region
More recently, the fragmented remains of ancient permanent teeth, including one right upper second molar and one left lower second molar, have been discovered in a cave called Lunadong, in China's autonomous region of Guangxi Zhuang. Elaborate dating techniques disclose that they may be as old as 126,000 years, suggesting that our modern human ancestors, may have departed their African homelands as much as 120,000 and perhaps even 130,000 years ago, in lieu of 60,000 previously thought. At least one tooth is almost certain to have belonged to a member of modern Homo sapiens, the species of bipedal primates to which modern humans belong[8]. As previously elaborated upon, this finding and others at Jebel Faya in the UAE has profound repercussions for the out of Africa theory of hominin development.
And in addition to all these species, the producers of the BBC documentary The Lost Tribes of Humanity (fn [1] below) make reference to a 5th "as yet unnamed" member of the human family discovered in Africa - a possible reference to Homo Naledi, discussed on the page Fossil finds
[1] “Giving accepted prehistoric history the finger – DNA tests reveal new group of ancestors”, SMH, 23.12.10. The contents of the article are drawn from an article appearing in the Journal Nature. See also footnote 18. Professor Paabo Svante discusses these developments in the BBC documentary The Lost Tribes of Humanity (2016) presented by Professor Alice Roberts of the University of Birmingham: www.bbc.co.uk/programmes/b07z8034/products
[2] Endogenous DNA comes from the bone itself, as distinct from the total DNA in a specimen, most of which comes from soil bacteria and other contaminants.
[3] The distinction between nuclear DNA (DNA drawn from a cell’s nucleus) and mitochondrial DNA (mtDNA drawn from very small compartments in the cell called mitochondria that are found randomly scattered in the cytoplasm outside the nucleus), as explained earlier. It includes only 37 genes inherited from the mother.
[4] “Non-Africans” because the commingling between species occurred outside that continent.
[5] Jamie Schreeve, “The case of the missing ancestor”, National Geographic, July 2013, 90 at 100. The hypothesis was advanced by team leader Svante Paabo at a Denisovan symposium in July 2001.
[6] Ibid, at 101.
[6.1] This is an edited summary of the article, "Chinese fossil sheds light on ancient human history", SMH, 3 May 2019:
https://www.smh.com.au/technology/chinese-fossil-sheds-light-on-mysterious-neanderthal-kin-20190502-p51jce.html [7] For h. floresiensis, see the page Fossil finds
[8] See Peter Spinks, ’Out of Africa’ theory of human evolution under fire”, SMH, 25 August 2014.