change at the blueprint level appears comparatively constant, the transition to a particular variant becoming ubiquitous can be rather rapid. the genes that drive the fundamental aspects of me having arms, legs, hands and so on are almost unchanged from bazillions of years ago and are fundamentally identical to those in fish. Fish make fins out of them, the whale chooses not to use them at all for hind legs, and I make legs ... but the genes are essentially identical. There are changes (mostly) in when current is applied to the circuit (the "switches") and chan ge in a switch can have a profound change. So, when digging up fossiles we see little change punctuated by lots of change. Genetically, we have a single base pair or two mutation that spreads rapidly owing to its success affording periods of apparent (fossils) massive change laid upon a more or less steady background of slow genetic change.
Humans, e.g., have (all of them) a broken verison of gene for making muscle ... a particular muscle, so we don't make the muscle. It is a jaw muscle, a huge one, so big that it needs a stout skull to leverage against. All of the great apes have this muscle, no humans do. The genetic change is 2 base pairs, next to nothing. Great apes skulls fuse solid at about 3 years, ours can grow some until we are about 30. If, we had this massive muscle our skull would be an exercise in plate tectonics. A couple of base pairs eliminates a muscle that relieves the requirement for early skull fusion ... result, our brains allowed to get bigger and bigger. A couple of bases. Pick up a few more changes on the kinetics of skull fusion and whatever feedback there is that restricts brain size to the container and whallah.
The thumb? Looks like perhaps a single base pair.
It is not that change at the genetic level changes much, the clock just ticks along creating diversity. Occasionally a particular change exhibits significant advantage, excludes the others and resets the rules on which all the other genes are then judged ... resets the filter for existing diversity, changing the frequency of extant alleles, not creating new faster change. So, frequency of alleles can move rapidly, but the underlying change is largely constant
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