[Sam Brown (OP)]

Daniel has asked us:

"I do get evolution and natural selection. Giraffes getting an always longer neck to get to the higher branches, or quicker, bigger, more energy efficient steps...

But, how on earth you get (evolutionary speaking) butterfly metamorphosis, where the whole caterpillar gets transformed?"

What do you think?

[Kryptid]

It wouldn't have been a matter of some mutation spontaneously giving a caterpillar the ability to transform into a butterfly. What you would expect would be a gradual differentiation between the different life stages over time. You start off with something that does not undergo metamorphosis at all, but only gets bigger each time it sheds its exoskeleton (like a silverfish). Over the generations, the insect gains genes through mutation and selection that are activated during different life stages to make the adult form slightly different from the immature form (such as with grasshoppers, which only gain wings during their final molt). Eventually, the number of differences between the immature and adult stages accumulate over time until you have something as different as a caterpillar and a butterfly (or a larva and a beetle).

[RD]

But, how on earth you get (evolutionary speaking) butterfly metamorphosis, where the whole caterpillar gets transformed?"

See ... https://www.scientificamerican.com/article/insect-metamorphosis-evolution/