This stability exists despite the incredible diversity seen today in wing patterns, sizes, and caterpillar forms across over 160,000 species globally, according to a new paper published in the journal Nature Ecology and Evolution.

It is rather like how fish can stay in the same place in a flowing river. They have to swim against the current. Similarly, in the absence of evolution, the genome would degrade due to accumulated mutations. Natural selection constantly selects against non-adaptive mutations. The genome of a creature which is as well adapted as it can be for a particular environment does not change because it cannot be better adapted than it already is.