By combining evidence from the fossil record with studies on insect anatomy and development, biologists have established a plausible narrative about the origin of insect metamorphosis, which they continue to revise as new information surfaces. The earliest insects in Earth’s history did not metamorphose; they hatched from eggs, essentially as miniature adults. Between 280 million and 300 million years ago, however, some insects began to mature a little differently—they hatched in forms that neither looked nor behaved like their adult versions. This shift proved remarkably beneficial: young and old insects were no longer competing for the same resources. Metamorphosis was so successful that, today, as many as 65 percent of all animal species on the planet are metamorphosing insects. – “How Did Insect Metamorphosis Evolve?”, Scientific American, August 10, 2012
The comments are the real story in this case. Note especially comment 10:
Having read this article three times I see no ‘explanation’. I simply see a series of observations tied together and set out as a broad rather vague theory.
One problem that seems apparent to the News desk around here is that the claim that “ young and old insects were no longer competing for the same resources” is nonsense.
Adult insects often do not live very long. Some hardly eat. Some don’t even have mouth parts. They mate and die.
And , to continue the species, they must lay eggs that produce young that are competing for the same resources with the young of many other insects, of their own species and others. So it is not clear just what food problem metamorphosis is supposed to have solved. What metamorphosis mainly does is enable the insect to travel easily to find a mate — something the wingless larva would be generally less able to do, left to its own devices. We still have no idea why it all happened this way.