Homo sapiens, Neanderthals and Denisovans… did they interbreed?

Recent discoveries in DNA have shed light on the relationship of Homo sapiens and extinct hominids, Homo neanderthalensis and Denisova hominins. There is evidence to suggest that all three lived around the same time, and possibly in the same area (Krause et al., 2010)(Meyer et al., 2012). If these three groups lived close together, it should be possible to detect whether or not theyinterbred. If H. sapiens interbred with H. neanderthalensis and D. hominins, we should be able to find genetic evidence of this interbreeding in modern H. sapiens genomes. Using modern genetic examination (Gibbons, 2010), scientists have determined that H. sapiens did interbreed with both H. neanderthalensis (Green et al, 2010)(Hawks, 2013)(Meyer et al, 2012) and with D. hominins (Hawks, 2013)(Meyer et al, 2012).

article-1058538-02B984B100000578-348_468x342Homo neanderthalensis fossils were first discovered in 1856 in Germany, and ever since, scientists have been exploring the relationship of Neanderthals to modern humans. (Gibbons, 2012) The first “draft sequence of the Neanderthal genome” was published in 2010 (Green, et al), and that has given us insight into the relationship of Neanderthal DNA to the DNA of modern humans. Using data obtained by the Human Genome Project (Intl Human Genome Sequencing Consortium, 2001), scientists can compare human and Neanderthal DNA in order to discover the genetic relationship between the two.  The evidence suggests that Neanderthals lived in both Europe and Asia before going extinct around 30,000 years ago (Green et al, 2010). However, many of the Neanderthals interbred with H. sapiens before going extinct. According to Green and colleagues (2010) andHawks (2013), modern humans living outside of Africa represent between 1% and 4% of ancestry from Neanderthal populations. It is possible, with modern genomic technology, for the average person to send a sample of her own DNA to a lab (ex: ‘23andMe’) and get results showing her ancestry. If she has European ancestry, it is possible that she will also have some small percentage of Neanderthal ancestry (Gibbons, 2012). These sorts of results would only be possible had the Neanderthals interbred with direct ancestors of modern humans. Not all of the evidence suggests that Neanderthals interbred with the ancestors of modern humans, however. A study showed that there were no contributions from Neanderthal mtDNA to modern human mtDNA from a specimen recovered from Mezmaiskaya Cave in the northern Caucasus. (Ovchinnikov, 2000) This is not necessarily contradictory data from the other studies; it shows that not all Neanderthal populations interbred with modern human populations.

Neanderthal_Man_2457005b

The Denisova hominins, when compared to the Neanderthals, have been studied in much less detail. This is partially due to the minimal amount of evidence scientists have regarding the Denisovans; nothing more than the DNA from two teeth and a finger found in a cave in Siberia, aging from between 74,000 – 82,000 years ago (Harmon, 2012). The DNA that scientists do have, however, allows a fairly substantial analysis of possible interbreeding with the ancestors of modern humans. Analysis shows that approximately 6% of modern Papuans’ DNA came from the Denisovans (Harmon, 2012). Research also shows that modern Australian and Melanesian people derive up to 5% of their ancestry from the Denisovan population (Hawks, 2013) An analysis of mtDNA shows that the Denisovans, Neanderthals and modern humans diverged approximately one million years ago, but the Denisovans themselves lived from around 30,000 to 50,000 years ago (Krausse, 2010). This data conflicts with the data from Harmon, showing that mtDNA sequencing and DNA sequencing indicate different time periods in which the Denisovans lived. The DNA evidence does suggest that ancestors of modern humans interbred with the Denisovans, but when they lived together isn’t known with much certainty. Cooper and colleagues (2013) confirm a date at more than 50,000 years ago and show that Denisovan and modern human ancestors interbred in remote Island Southeast Asia.

135998_083Scientists may not know exactly when the interbreeding happened and we have reason to believe that it wasn’t extremely common, but the data presented in the wide variety of research clearly shows that the direct ancestors of Homo sapiens interbred with both Homo neanderthalensis and Denisova hominins. By understanding the relationships between all three groups, this information will lead to a better understanding of human history. By gaining a better understanding of modern human ancestry, we can determine the differences that may have caused the rise of H. sapiens and the decline (and ultimate extinction) of H. neanderthalensis and D. hominins. 

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References:

  • Cooper, A. & C. B. Stringer. (2013) “Did the Denisovans Cross Wallace’s Line? Science.
  • Green, Richard E., et al. 2010. A Draft Sequence of the Neanderthal Genome. Science.
  • Gibbons, Ann. 2010. “Tiny Time Machines Revisit Ancient Life” Science
  • Gibbons, Ann. 2012. “The Neanderthal in My Family Tree; New genetic evidence shows our ancestors interbred with now-extinct species.” The Big Questions – What Makes Humans Human.
  • Harmon, K. 2012. “New DNA Analysis Shows Ancient Humans Interbred with Denisovans”. Nature News.
  • Hawks, John. 2013. “Significance of Neandertal and Denisovan Genomes in Human Evolution” Annual Review of Anthropology.
  • International Human Genome Sequencing Consortium. 2001. “Initial Sequencing and Analysis of the Human Genome”. Nature.
  • Krause, J., et al. 2010. “The complete mitochondrial DNA genome of an unknown hominin from southern Siberia”. Nature.
  • Meyer, M. A., et al. 2012. “High Coverage Genome Sequence from an Archaic Denisovan Individual”. Science

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This paper was originally a small research project for my Science Writing (bio389) class at SUNY at Buffalo State College

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