Our inheritance from the Neanderthals

Decoding history: Modern human population in the Bacho Kiro cave region had interbred with the ‘locals’ and produced a cross-bred group of people  

While people like me, in their eighties, use the wrist watch to know the time of the day, today’s ‘hip’ youngsters, typically clad in blue jeans with pre-planned rips at the right place and a watch carrying facilities that not only tell the time but also the right tweets, movies and music of the present day. Compared to them, people like me are museum pieces. But when I challenge some of the more ‘knowledgeable’ among them, about how early this technological advance has come about, they proudly point out that right here in India, there is the Qutub Minar and its Iron Pillar in Delhi, both from the Iron Age.

Modern humans

‘Modern’ humans have populated the earth from long before the Iron Age, for some 300,000 years, cohabiting Mother Earth along with other pre-human hominins. Who were these other people? Because bones of one of these ‘others’ were first discovered in the Neander valley, just east of Dusseldorf in Germany, they were called ‘Neanderthals’. This hominin arose about 430,000 years ago and did not evolve in Africa, as Homo sapiens did. Early humans first encountered them when they migrated out of Africa.

Compete or co-operate

Did they compete with us Homo sapiens, or was there cooperation? Answers to such questions have come, one fragment at a time, from studies on the genetics of populations from Asia and Europe in places where migration brought the two species face to face. The techniques for these analyses are also advancing rapidly – all you need today is a bone fragment or, even better, a tooth – these are drilled to remove a few milligrams of powder, from which DNA is extracted and sequenced. Sometimes, you don’t even need the fragment, dwelling places like caves have extractable DNA in their sediments! Notable driving forces behind all these technical and intellectual advances in this field include the Swedish geneticist Svante Pääbo and the biochemist Johannes Krause.

‘Modern’ humans interbred with the locals in these regions. Recently a thigh bone of such a cross-bred individual became available, as Dr Ann Gibbs points out in her column titled, ‘When modern humans met Neanderthals’, (Science, 9 April 2012: vol 372, issue 6538, pp. 115-116, DOI:10.1126/science.372.6538.115). A more recent genetic analysis of one set of samples from the region showed that Neanderthals came to the Bacho Kiro cave in Bulgaria first, more than 50,000 years ago and left their stone tools. Next came modern humans in two or more waves, and littered the cave with beads and stones about 45,000, and then 36,000 years ago. Genome-wide data of three human males who lived in this cave 45,000 years ago show that all three had Neanderthals in their family lineage, from just a few generations ago. This clearly showed that the modern human population in that region had interbred with the ‘locals’ and produced a cross-bred group of people – modern with Neanderthals. This cross-bred group had 3.4%–3.8% Neanderthal ancestry (in modern non-Africans it is about 2%). The inheritance was in the form of long chunks of chromosomal segments, which grew shorter with each generation. By measuring the size of these chunks, it is estimated that these three residents had a Neanderthal ancestor 6–7 generations ago. In another study, a nearly intact feminine skull from the Zlatý kůň hill in the Czech Republic, roughly as old as the Bachi Kiro gentlemen, was found to have Neanderthal ancestors going back about 70 generations (2,000 years).

Genetic connections

Tracing the genetic lineages of these four individuals, it is somewhat surprising that no traces are to be found among today’s Europeans. However, they are connected to present-day East Asians and Native Americans. The descendants of these Eurasian cave dwellers appear to have packed up and moved eastward, finally enduring the hardship of crossing an ice-age Bering Strait, and the luxury of visa-free travel, into the Americas.

Conferring immunity

Further studies on the genomes of the Neanderthals themselves allow a comparison with those of modern humans (see reference above) and give us a glimpse of the genetic changes in the DNA sequences of the two. The chunks inherited from Neanderthals were whittled down to 2%, but what advantages did these newly acquired genes confer on humans? Having adapted to colder regions for 400,000 years, the Neanderthals gave us out-of-Africa humans variations in skin and hair colour better suited to the cold, as well as adaptive variants for metabolism and immunity – to help better adjust to strange new food sources and to unfamiliar disease-causing viruses in the new environment.

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Printable version | Nov 27, 2021 9:13:11 PM |

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