Denisovans and Other Mysterious Hominins Ancient DNA shows that Neanderthals and modern humans interbred
• Initial mtDNA studies indicated that there was no admixture with humans.
• mtDNA is not sufficient for making claims about admixture. Nuclear DNA is always needed.
• Nuclear DNA studies now show that there was admixture between Neanderthals and humans (Green et al. 2010; Prufer et al. 2014). – All non-Africans derive ~2% ancestry from Neanderthals. – Admixture took place in the Near East or South Asia before East Asian and West Asian modern human populations split.
Admixture occurred when humans spread into the Neanderthal’s range in the Near East ca. 54-49kya. As humans continued to expand into other parts of Eurasia, they brought Neanderthal ancestry with them.
Green, R. E., et al. (2010). A draft sequence of the Neandertal genome. science, 328(5979), 710-722. http://www.sciencemag.org/site/special/neandertal/feature/index.html Prüfer, K. et al. (2014). The complete genome sequence of a Neandertal from the Altai Mountains. Nature, 505(7481), 43. Outline of Today’s Class: Denisovans and Other Mysterious Hominins
1) The Denisovans - A genome without a fossil - Interactions between hominin populations in Eurasia
2) Descendants of Homo erectus in Asia - Homo floresiensis
3) Homo naledi After Homo erectus, several species of archaic Homo emerged during the Middle Paleolithic
Homo heidelbergensis, Neanderthals, and Denisovans are often called “Archaic Homo” or “Archaic Humans”
Neanderthals Homo sapiens Denisovans (400-30kya) (200kya-present) (40kya) Europe and Middle East Africa first Asia
Homo heidelbergensis (600-200kya) Africa, Europe, and the Middle East
Homo erectus (2mya-150kya?) Africa and Asia. Europe? Denisova Cave in the Altai Mountains Denisovans: A Genome without a Fossil Record
• DNA extracted from a few teeth and fragments of finger bones dated to 41kya.
• Identification of new species of hominin called the “Denisovans” (Reich et al. 2010; Meyer et al. 2010).
• Are there other Denisovan fossils?
• How many hominin species were there in Eurasia?
Meyer, M., et al. (2012). A high-coverage genome sequence from an archaic Denisovan individual. Science, 338(6104), 222-226. Reich, D. et al. (2010). Genetic history of an archaic hominin group from Denisova Cave in Siberia. Nature, 468(7327), 1053-1060. Denisovan Admixture
• The MRCA for humans, Neanderthals, and Denisovans lived 550-765kya. Neanderthals and Denisovans share a more recent ancestor that lived 450kya (Reich et al. 2010, 2011; Sankararaman et al. 2016).
• Denisovans and Neanderthals interbred. Both had low genetic diversity and small population sizes (Prufer et al. 2014).
• Denisovans and humans interbred in Asia. Living human populations in Australia and Papua New Guinea retain 3-6% Denisovan DNA signatures.
• Denisovans also interbred with another unidentified hominin, possibly a relative of Asian Homo erectus (Prufer et al. 2014).
Prüfer, K. et al. (2014). The complete genome sequence of a Neandertal from the Altai Mountains. Nature, 505(7481), 43. Reich, D. et al. (2010). Genetic history of an archaic hominin group from Denisova Cave in Siberia. Nature, 468(7327), 1053-1060. Reich, D. et al. (2011). Denisova admixture and the first modern human dispersals into Southeast Asia and Oceania. The American Journal of Human Genetics, 89(4), 516-528. Sankararaman, S., et al. (2016). The combined landscape of Denisovan and Neanderthal ancestry in present-day humans. Current Biology, 26(9), 1241-1247. Latest News! First Generation Neanderthal and Denisovan Offspring Found in Denisova Cave!
Ancient DNA reveals that “Denisova 11” was a first generation hybrid female that lived 80kya. Her mother was Neanderthal and her father was Denisovan. Admixture among hominin populations was more common in Upper Paleolithic Eurasia than we once thought.
Only individuals from whom sufficient nuclear DNA fragments have been recovered to enable their attribution to a hominin group are shown. Full or abbreviated names of specimens are shown near each individual. Blue, Neanderthals; red, Denisovans; yellow, ancient modern humans. Asterisks indicate that the genome was sequenced to high coverage; individuals with an unknown sex are marked with a question mark. Note that Oase 1 has recent Neanderthal ancestry (blue dot) that is higher than the amount seen in non-Africans. Denisova 3 has also been found to carry a small percentage of Neanderthal ancestry.
Slon, V. et al. (2018). The genome of the offspring of a Neanderthal mother and a Denisovan father. Nature 561: 113-116. A Revised Model for Human Origins: “Out of Africa with Admixture”
1. Homo erectus gave rise to Homo heidelbergensis in Africa and Western Eurasia.
2. Homo heidelbergensis gave rise to additional forms of archaic humans in Eurasia (Neanderthals and Denisovans).
3. There was some gene flow between the various forms of archaic humans outside of Africa.
4. Modern humans evolved from Homo heidelbergensis in Africa.
5. Modern humans replaced other archaic humans, but there was a low level of gene flow between humans and these other groups.
6. Some transitional forms of hominin that evolved directly from Homo erectus persisted in Asia.
Qiu (2016) Current Summary of Evolutionary Relationships
Separate branch for the Asian descendants of Homo erectus
Early expansions of modern humans out of Africa ca. 100kya
Nielsen, R., et al. (2017). Tracing the peopling of the world through genomics. Nature, 541(7637), 302-310. Homo floresiensis (“The Hobbit”) Homo floresiensis • Several individuals found in Liang Buo Cave, Flores Island, Indonesia.
• Fossil hominin with many archaic traits that look similar to Homo erectus. Shows persistence of archaic Homo populations in East Asia.
• Small size due to “island dwarfism.”
• Originally dated to 18kya (significant overlap with modern humans).
Watch the 5 minute video: http://humanorigins.si.edu/multime dia/videos/hobbits-flores-indonesia Homo floresiensis—New Dates
• March 2016, archaeologists announced new dates of 700kya-50kya.
• Still potential overlap with modern humans, but much more ancient than the original dates suggested.
• Are there other hominins that have not been discovered yet? East Asia may have been home to several diverse archaic human species. Africa may have also been home to other hominin species that survived until quite recently.
Rising Star cave, South Africa: Homo naledi (ca. 300kya) discovered in 2013.
“Dawn of Humanity” Nova video : http://www.pbs.org/wgbh/nova/evolution/d awn-of-humanity.html
Berger, L.R., et al. (2015). Homo naledi, a new species of the genus Homo from the Dinaledi Chamber, South Africa. eLife 2015;4:e09560 Next week…global migrations!