Wednesday, 4 December 2013

Unravelling Our Evolutionary Past

BBC News - Leg bone gives up oldest human DNA

New evidence which may help unravel the complicated story of human evolution was published in Nature today. Researchers led by Matthias Meyer at the Max Planck Institute for Evolutionary Anthropology in Leipzig have isolated and analysed mitochondrial DNA from 400,000 year-old hominid fossils found at the Sima de los Huesos or 'pit of bones' in the Atapuerca mountains in northern Spain.

Scientifically, the significance of this is that this is the oldest hominid DNA yet recovered. Until recently it was assumed that DNA degrades over time at a rate which means 60,000 years was the limit beyond which DNA would not be recoverable but new techniques in DNA sequencing have now pushed that back way beyond what was thought possible.

Science can tell only so much from bones and fossils but DNA potentially provides a much clearer picture of evolutionary relationships and the recovery of mitochondrial DNA raises the possibility of a being able to recover the full genome.

Mitochondrial DNA (mtDNA) is from the cell organelles responsible for using the energy in glucose to build adenosine triphosphate (ATP) which the cell can then use as an energy source to drive other metabolic processes. These organelles are believed to be the descendants of a bacterium which formed a symbiotic relationship with other simple cells to form the complex cells of which all multicellular life is composed. Mitochondria are present in the ovum but not in sperm, so we only inherit mtDNA from our mother and it does not get shuffled up and mixed with our father's DNA, unlike most of our genome, so it is possible to construct a tree of relationships through the maternal line.

Atapuercan family - artist's impression
(From Pilgrimage Day 13: Belorado - Atapuerca DR. Kaare Torgny Pettersen)
At 400,000 years old, researchers had expected this mtDNA to show the hominids to be close to the Neanderthals who are believed to have been in Euro-Asia for at least 250,000 years, so it was something of a surprise that they are actually closer to the recently-discovered Denisovans from Siberia. Physically, the fossils from Sima de los Huesos look like early Neanderthals and this has led some paleoanthropologists to classify them as Homo heidelbergensis which is a candidate for the forerunner of H. neanderthalensis, the as yet unnamed Denisovans, a third possible cousin known only from the DNA it is thought to have contributed to modern humans, and maybe even H. sapiens.

One possibility is that this population resulted from interbreeding between early Neanderthals or Homo heidelbergensis and H. erectus as humans expanded into Euro-Asia and diversified, forming what amounts to a ring species. This is of course to be expected as species diversify from a common ancestor to form regional varieties, subspecies and eventually new species. There will inevitably be a period during which fertile interbreeding is possible. It is also possible that the Denisovans were the descendants of an early expansion which was later replaced in Europe and Western Asia by Neanderthals who had evolved in isolation before moving into their final range as an Ice Age adapted human variant, to be replaced in their turn by H. sapiens only some 30-50,000 years ago as the ice retreated and Neanderthals found themselves specialised for an environment which no longer existed. For them, global warming happened 30,000 years ago.

Whatever the final resolution to this puzzle turns out to be, and DNA sequencing is bringing that ever closer, we can be absolutely sure it will not trace all humans to a boat in the Middle East some 4000 years ago. The Max Planck Institute in Leipzig, and the science of DNA sequencing and analysis, must be giving nightmares to the professional liars at the Discovery Institute and the Institute for Creation Research which are desperate to keep selling their primitive Bronze-Age mythology to scientifically illiterate simpletons, hoping to be swept to political power on a wave of scientific ignorance and arrogant incredulity.

The science, of course, is proving to be entirely consistent with the neo-Darwinian model for evolution. Indeed, the science only makes any sense in terms of Darwinian Evolution.

'via Blog this'

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2 comments :

  1. Great article indeed Rosa , but why you make a lot of restriction for commenting ,if the user write a good comment and leave a link for his website like WordPress as u know so what is the problem then .I'm agree with you about spammy comments they should be killed ..lol , please keep writing Rose

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    1. There are no restrictions on including links in comments. However, if the comment is obviously spam, it will be removed. The comment section is for discussing the contents of the article, not for being parasitised by attention-seekers and time-wasters.

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