Does our genes determine our life? This question has been popular during last century when DNA was discovered as a responsible molecule for inheritance. That belief has been shattered once observations regarding additional layer of regulation, termed epigenetics began to pour in. Now what if some of the DNA in our genome is not ours at the first place? Then, for the second time there is addition of complexity surrounding our genes and its inheritance.
According to recent observations, At least 2% of human genome could be directly traced to Neanderthals. Amazing isn't it? The story goes like this, As ancient humans travelled out of Africa from their cradle of their origin they encountered Neanderthals which were already thriving in Europe. Humans were not well adapted to those colder climates but Neanderthals had already expanded through the vast lands of Eurasia. It has been speculated that various episodes of tragic violence between two species might have led to Neanderthals extinction but their story of love has etched its mark on our DNA. According to some evidence, Neanderthals interbred with early human for upto 50,000 years. The success of this inter-species breeding spree can be inferenced from the fragments of DNA which are present only in humans of non-african descent. As some groups of humans left Africa they bred with Neanderthals and left progenies. Their expansion in those regions carried within them DNA of Neanderthals but the DNA of the African descent remained same. Now the analysis of the genomes of both African and non-african genomes reveals huge chunks of DNA which are absent in African ancestry which points out the source of DNA to the Neanderthals. So, every non-african descendants have Neanderthal DNA inside them. By this estimate, 60 million nucleotide inside us are of Neanderthal origin.
This tremendous observation have led to avalanche of new question regarding its position and expression in human genome. One of the question asked by McKoy et al. was to identify the reach of Neanderthal gene expression in human tissues. They wanted to know the variations in gene expression in different tissues. Interestingly they found that significant downregulation of Neanderthal genes takes place in human brains and testis as compared to other tissues. The most important difference between humans and other species is its brain. This fits beautifully with the evolutionary pressure to preserve the survival of brains. As the brains evolved so did its divergence from its initial microenvironment. Any major influence of Neanderthal genes compromised the survival of the hybrids with probably lethal consequences. Thus, 'expressional reach' of Neanderthal genes was attenuated as humans continued to evolve. Neanderthal genes in testis also had less 'expressional reach' because it might have reduced the reproductive fitness of hybrid Human-Neanderthal individuals in which it over-expressed. Those individuals might have died before they reached sexual maturity.
Natural selections seems to strongly selected limited influence of Neanderthal genes in brain and testes for optimal survival and reproduction in the modern humans. But what influence does these regions have on other regions of our genomes? What is It's evolutionary advantages to humans? Whether these Neanderthal chunks of DNA makes modern humans prone to certain diseases remains to be explored in further detail.
Reference:
McCoy, R. C., Wakefield, J., & Akey, J. M. (2017). Impacts of Neanderthal-Introgressed Sequences on the Landscape of Human Gene Expression. Cell, 168(5), 916-927.
According to recent observations, At least 2% of human genome could be directly traced to Neanderthals. Amazing isn't it? The story goes like this, As ancient humans travelled out of Africa from their cradle of their origin they encountered Neanderthals which were already thriving in Europe. Humans were not well adapted to those colder climates but Neanderthals had already expanded through the vast lands of Eurasia. It has been speculated that various episodes of tragic violence between two species might have led to Neanderthals extinction but their story of love has etched its mark on our DNA. According to some evidence, Neanderthals interbred with early human for upto 50,000 years. The success of this inter-species breeding spree can be inferenced from the fragments of DNA which are present only in humans of non-african descent. As some groups of humans left Africa they bred with Neanderthals and left progenies. Their expansion in those regions carried within them DNA of Neanderthals but the DNA of the African descent remained same. Now the analysis of the genomes of both African and non-african genomes reveals huge chunks of DNA which are absent in African ancestry which points out the source of DNA to the Neanderthals. So, every non-african descendants have Neanderthal DNA inside them. By this estimate, 60 million nucleotide inside us are of Neanderthal origin.
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| Human skull on the left as compared to Neanderthal (source: Wikimedia Commons/Dr. MikeBaxter) |
Natural selections seems to strongly selected limited influence of Neanderthal genes in brain and testes for optimal survival and reproduction in the modern humans. But what influence does these regions have on other regions of our genomes? What is It's evolutionary advantages to humans? Whether these Neanderthal chunks of DNA makes modern humans prone to certain diseases remains to be explored in further detail.
Reference:
McCoy, R. C., Wakefield, J., & Akey, J. M. (2017). Impacts of Neanderthal-Introgressed Sequences on the Landscape of Human Gene Expression. Cell, 168(5), 916-927.
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