The issue with Time and Evolution
Posted: Thu Mar 12, 2015 12:13 pm
http://www.nature.com/news/dna-mutation ... et-1.17079
Part of the article:
Part of the article:
In the past six years, more-direct measurements using ‘next-generation’ DNA sequencing have come up with quite different estimates. A number of studies have compared entire genomes of parents and their children — and calculated a mutation rate that consistently comes to about half that of the last-common-ancestor method.
A slower molecular clock worked well to harmonize genetic and archaeological estimates for dates of key events in human evolution, such as migrations out of Africa and around the rest of the world1. But calculations using the slow clock gave nonsensical results when extended further back in time — positing, for example, that the most recent common ancestor of apes and monkeys could have encountered dinosaurs. Reluctant to abandon the older numbers completely, many researchers have started hedging their bets in papers, presenting multiple dates for evolutionary events depending on whether mutation is assumed to be fast, slow or somewhere in between.
Last year, population geneticist David Reich of Harvard Medical School in Boston, Massachusetts, and his colleagues compared the genome of a 45,000-year-old human from Siberia with genomes of modern humans and came up with the lower mutation rate2. Yet just before the Leipzig meeting, which Reich co-organized with Kay Prüfer of the Max Planck Institute for Evolutionary Anthropology, his team published a preprint article3 that calculated an intermediate mutation rate by looking at differences between paired stretches of chromosomes in modern individuals (which, like two separate individuals’ DNA, must ultimately trace back to a common ancestor). Reich is at a loss to explain the discrepancy. “The fact that the clock is so uncertain is very problematic for us,” he says. “It means that the dates we get out of genetics are really quite embarrassingly bad and uncertain.”