Protein clock dating

Molecular clocks For the past 40 years, evolutionary biologists have been investigating the possibility that some evolutionary changes occur in a clock-like fashion.Over the course of millions of years, mutations may build up in any given stretch of DNA at a reliable rate.When a stretch of DNA does indeed behave like a molecular clock, it becomes a powerful tool for estimating the dates of lineage-splitting events.For example, imagine that a length of DNA found in two species differs by four bases (as shown below) and we know that this entire length of DNA changes at a rate of approximately one base per 25 million years.One major issue of using sequence data to infer absolute divergence times is how to disentangle time from evolutionary rates.Because of this, the absolute time since the last common ancestor for species must then be calculated by calibrations based on paleontological evidence.This general technique has been used to investigate several important issues, including the origin of modern humans, the date of the human/chimpanzee divergence, and the date of the Cambrian "explosion." Using molecular clocks to estimate divergence dates depends on other methods of dating.

Since each lineage experienced its own evolution, the two species must have descended from a common ancestor that lived at least 50 million years ago.

The divergence times appeared to be robust with respect to prior assumptions and paleontological calibrations.

Interestingly, these relaxed clock time estimates are much more recent than those obtained under the assumption of a global molecular clock, yet bilaterian diversification appears to be ≈100 million years more ancient than the Cambrian boundary.

Reconstructing and dating the early evolutionary history of eukaryotes have proven challenging questions due to the scarcity of the fossil record, especially for protists (1).

In the Archean eon, biomarker compounds characteristic of possibly extinct stem eukaryotes are found ≈2,700 million years ago (Mya) (2).

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That is, differences between sequences would accumulate in a linear fashion.

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