Mutations are changes to the letters of DNA’s genetic code – for instance, a nucleotide Guanine (G) becomes a Thymine (T).These changes will be inherited by future generations if they occur in eggs, sperm or their cellular precursors (the germline).Moreover, relevant fossils or artifacts have not been discovered for all milestones in human evolution.
However, these methods require ancient remains to have certain elements or preservation conditions, and that is not always the case.
First they compare the DNA sequences of two individuals or species, counting the neutral differences that don’t alter one’s chances of survival and reproduction.
Then, knowing the rate of these changes, they can calculate the time needed to accumulate that many differences.
But in aggregate, over many generations, these changes lead to substantial evolutionary variation.
Scientists can use mutations to estimate the timing of branches in our evolutionary tree.