Douglas, my own bias is to think that evolution has given us 3 billion+ years of selection for evolving faster. And multicellular organisms (a small minority of the total but interesting to us) have found ways to make genetic "modules" that result in phenotypes which fit together in a modular way. Chordates build a variety of structures from keratin. Arthropods build a big variety of limbs. Etc. The body plans that are most flexible speciate into the largest variety of niches -- nematodes, arthropods, mollusks, and chordates, and you have the big majority of animal species in just those 4 phyla.

We don't make just random changes, we have "hotspots" that change a lot while others are mostly held fixed. A big variety of mechanisms evolved that encourage faster evolution, because those mechanisms are themselves selected.

Apologies for the off-topic note.