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What does MCH stand for?

MCH stands for Molecular Clock Hypothesis

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Since fish diverges from the main stem of vertebrate evolution earlier than either birds or mammals, the cytochrome c of both mammals and birds should be equally different from the cytochrome c of fish. Similarly, all vertebrate cytochrome c should be equally different from the yeast protein. "[2] For example, the difference between the cytochrome c of a carp and a frog, turtle, chicken, rabbit, and horse is a very constant 13% to 14%. Similarly, the difference between the cytochrome c of a bacterium and yeast, wheat, moth, tuna, pigeon, and horse ranges from 64% to 69%. Together with the work of Emile Zuckerkandl and Linus Pauling, the genetic equidistance result directly led to the formal postulation of the molecular clock hypothesis.
The key to using biological molecules as molecular clocks is the hypothesis of neutral evolution. This hypothesis states that most of the variability in molecular structure does not affect the molecule's functionality. This is because most of the variability occurs outside of the functional regions of the molecule. Changes that do not affect functionality are called "neutral substitutions" and their accumulation is not affected by natural selection.
Most discussions of the rates of DNA evolution have been with respect to the molecular clock hypothesis which states that there is a positive linear relationship between time since two species diverged and amount of genetic divergence (e. g. , DNA sequence difference) between those species. These observations stated above indicate that there is not one molecular clock but probably many molecular clocks that "tick" at different rates.
Those scientist that continue to try and revise the molecular clock hypothesis.