Metamorphosis is the radical development plan of shedding one body for a different one altogether. The price of metamorphosis is high. Tearing apart an anatomy and building a new one burns a lot of calories. Metamorphosis is a complicated process which can go awry, resulting in defects. Metamorphosis takes time, leaving an animal vulnerable to predators and parasites.
Yet 80% of all animals experience metamorphosis: from jellyfish to butterflies to flatfish to frogs. This common life-history strategy arose only a few times. Once metamorphosis appears it rarely is abandoned for a different development cycle.
Metamorphosis is not easy to evolve but hard to lose. ~ Dutch evolutionary biologist Hanna ten Brink et al
Many foods are seasonal. Metamorphosis offers the distinct advantage of being able to change food source.
In some vertebrates, metamorphosis is camouflaged, but it is never lost. ~ French biologist Vincent Laudet
Our birth is a metamorphosis in more than swapping food supply. Leaving the womb sparks major tissue changes, governed by some of the same hormones that spark more amazing changes in other animals.
Metamorphosis also affords the means to change locomotion, and so expand range. Under a metamorphosis program, the extensive equipment necessary for mating need not develop until adulthood. Starting small and metamorphizing into a different vehicle offers an economy which cannot be achieved any other way.