Protein clock dating

15 May

This is significant because it allows anthropologists to trace patterns of migration and settlement, which gives helpful insight as to how contemporary populations have formed and progressed over time.

Molecular anthropology has been extremely useful in establishing the evolutionary tree of humans and other primates, including closely related species like chimps and gorillas.

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 theory proposed that most of the substitutions that we observe in molecular data (and the variation we see within species at the molecular level) is due to the fixation of these changes that are neutral or nearly neutral with respect to selection.

This theory also provided an important null model of molecular evolution, but was not without its critics.

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.

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

In addition, they suggested that this uniform rate of a specific protein would be approximately constant, not just over evolutionary time, but also across different lineages or taxonomic groups.

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.