|MadSci Network: Evolution|
The process of metamorphosis has long been touted by creationist to be definitive proof that evoution cannot be correct, because it is too complex, and there are no possible intermediates. There are fundamental flaws in their argument, but I will stick to the question at hand.
It is true that metamorphosis has stumped many scientists for quite some time. But in fact, in September of last year an article was published in Nature, a scientific journal, by two scientists, JW. Truman and LM. Riddiford, that dealt with the problem. Here is the abstract of the article, which is titled, "The origins of insect metamorphosis."
"Insect metamorphosis is a fascinating and highly successful biological adaptation, but there is much uncertainty as to how it evolved. Ancestral insect species did not undergo metamorphosis and there are still some existing species that lack metamorphosis or undergo only partial metamorphosis. Based on endocrine studies and morphological comparisons of the development of insect species with and without metamorphosis, a novel hypothesis for the evolution of metamorphosis is proposed. Changes in the endocrinology of development are central to this hypothesis. The three stages of the ancestral insect species-pronymph, nymph and adult-are proposed to be equivalent to the larva, pupa and adult stages of insects with complete metamorphosis. This proposal has general implications for insect developmental biology."
Decoding that can be a little bit tricky. What it says is that the original state for insects was to not undergo metamorphosis, but to gradually change from a pronymph to a nymph then to the adult. What happened was that at some point, changes in the hormones of the insects caused them no longer to develop in such a steady fashion, but to develop in bursts. So the new, metamophosing insects would stay the same for a while, then suddenly change, instead of gradually changing all the time.
Why is that an advantage for the insect? When you have an insect that has, for example, two forms, like a caterpillar and a moth, the two stages are so completely different that they no longer compte with each other. The moth eats nectar, and the caterpillar eats leaves. There is no competition between the two, as there would be in a continually developing insect that ate both at some point. This lessening of interspecies competition was a great help in allowing the species to propogate itself. Along with the lessening of the competition was teh ability to take ofver new niches. A caterpillar and a butterfly could occupy different places in teh ecosystem - this allowed for great diversification - another thing that has helped insects becoms so succesful.
So insects that developed metamorphosis really did have a great advantage over those that didnt. But we still have insects that do not undergo metamorphosis, and we also have something of an intermediate between the two, called incomplete metamorphosis, that could concievably be a linker between the two - something the creationists dont want to hear at all.
Ill give you the complete reference to the article I quoted above, so you can go look it up at the nearest university if you want. Ill also give you a web page that gives a different explanation, and more info in general.
I hope that answered you question, and thanks for using the Mad Scientist
Truman JW. Riddiford LM.
Department of Zoology, University of Washington, Seattle 98195-1800, USA. email@example.com
The origins of insect metamorphosis.
Nature 401(6752):447-52, 1999 Sep 30.
Does Butterfly Metamorphosis Disprove Evolution?
Try the links in the MadSci Library for more information on Evolution.