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"The theory of a molecular clock is based on the premise that all DNA mutates at a certain rate. It is not always a steady rate but it evens out over the millennia and can be used to track evolution.

This theory does not seem correct on the face of it.

Aren't there bursts of evolution when climate or environments change, followed by millions of years of relative stability?

Aren't there bursts of evolution when climate or environments change, followed by millions of years of relative stability?

Quite a bit of the DNA code is "junk", not required for the creature to survive. Mutations in the required parts of DNA tend to be weeded out of the genome because the critter may not survive with those errors, but changes in the junk DNA happen at a relatively steady rate, and are passed down and can be measured.

The "bursts of evolution" you talk about, often associated with environment changes, exploit mutations in the non-junk DNA and result in separate species.

I think this is how it works. I don't claim to be a genetic scientist.

I believe they study regions of DNA that are considered "junk;" theory has it that junk DNA doesn't code for anything particular in the phenotype, and would therefore not be subject to selective pressures, only random mutations.

And there are reasons to believe that the rate of occurrence of these mutations, due to the random processes of thermal action and ionizing radiation, is roughly constant over the long term.

Very recent research, however, is questioning just how "junky," or non-functional, this DNA actually is. One subtle use for junk DNA might be to facilitate the folding of long DNA chains into usefully compact forms. (Chromosomes are such long DNA molecules that they critically depend on a large amount of folding.)

Another interesting theory about junk DNA is that it serves to intercept ionizing events relative to its proportion in the overall DNA structure, thus reducing the probability or frequency of harmful mutations to non-junk DNA. Sort of the way a larger herd of wildebeests minimizes the chances of any particular one getting caught by a lion. < }B^)