Molecular dating rates vary

03-Nov-2017 06:46 by 6 Comments

Molecular dating rates vary

When scientists say that modern humans emerged in Africa about 200,000 years ago and began their global spread about 60,000 years ago, how do they come up with those dates?Traditionally researchers built timelines of human prehistory based on fossils and artifacts, which can be directly dated with methods such as radiocarbon dating and Potassium-argon dating.

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Moreover, relevant fossils or artifacts have not been discovered for all milestones in human evolution.By applying these methods to the ever-growing database of DNA from diverse populations (both present-day and ancient), geneticists are helping to build a more refined timeline of human evolution.Molecular clocks are based on two key biological processes that are the source of all heritable variation: mutation and recombination.Because mutations accumulate so slowly, this clock works better for very ancient events, like evolutionary splits between species.The recombination clock, on the other hand, ticks at a rate appropriate for dates within the last 100,000 years.As recombination occurs in each generation, the bits of Neanderthal ancestry in modern human genomes becomes smaller and smaller over time.

Genetic changes from mutation and recombination provide two distinct clocks, each suited for dating different evolutionary events and timescales.Large discrepancies have been found in dates of evolutionary events obtained using the molecular clock.Twofold differences have been reported between the dates estimated from molecular data and those from the fossil record; furthermore, different molecular methods can give dates that differ 20-fold.View the full list DNA holds the story of our ancestry – how we’re related to the familiar faces at family reunions as well as more ancient affairs: how we’re related to our closest nonhuman relatives, chimpanzees; how mated with Neanderthals; and how people migrated out of Africa, adapting to new environments and lifestyles along the way.And our DNA also holds clues about the timing of these key events in human evolution.First they compare the DNA sequences of two individuals or species, counting the neutral differences that don’t alter one’s chances of survival and reproduction.