[bennysaurus]

It's an intriguing idea though if nothing else. A question here (I don't know your background if it's biology mind you): what actually happens in the metamorphosis between caterpillar and butterfly/moth or any larval animal for that matter?

It does seem rather radical to switch off a massive amount of genes and switch on a bunch of others in adulthood, drastically changing your physical form.

[polyfractal]

Nah, you can consider puberty to be a less extreme form of metamorphasis. Hundreds of genes are switched on and off to accomplish rather drastic sexual and physical changes.

Switching genes is cheap and easy. You have dozens of genes that switch on/off acting as pacemakers and timers. You have other genes that switch on when there is a boost of insulin, and then turn back off once the insulin is gone. There are genes that are only turned on when stressed, hypoxic, over-temperature, under-temperature, over-fed, underfed, growing, not growing, genes that turn on when neurons are excited or inhibited. The list is endless.

If you think of your body as one giant state machine, it makes sense that you need thousands of flags to control the exact state that it is in.

It's actually much more complicated, since genes really aren't binary. Each gene is also a scalar, producing varying quantities of protein, or causing various kinks in the DNA which affects nearby genes (called "enhancers"). So really, you have a bunch of binary states which are then modulated by the amount of protein that is being created.

Then you have different parts of a gene that can be individually turned on/off, producing different isoforms of a single protein. Each isoform has different capabilities, especially when paired with regulatory proteins that modulate it's behavior (which also have their own regulation at the genetic and proteomic level). And each of these proteins in turn effects an numerable array of other proteins and genes, cascading throughout the entire system.

The body is a remarkably vast state machine.

Edit: This is totally ignoring all the microRNA and shRNA which modulates the state between DNA translation and transcription. Basically, add a few more million states to the state machine.

[gus_massa]

Sorry, I don't enough about what happens during the metamorphosis. I hope that someone can answer that. (Another question: If the caterpillar lost a leg, the butterfly has a missing leg?)

Changing the form is very popular between insects. (Almost?) All of them do it. For example:

* Grasshoppers: http://commons.wikimedia.org/wiki/File:Snodgrass_Melanoplus_...

* The young grasshoppers look like small wingless grasshoppers, so it is not a surprising transformation (if you ignore the wings and some internal details)

* Ants: http://askabiologist.asu.edu/individual-life-cycle

* Bees: http://www.magicpest.com/the-life-cycle-of-an-arizona-bee/

* The young ants / bees look like eggs, because they live safely inside the hive, and get the food from their sisters. So we don't have a special name for them.

* Mosquitoes: http://www.mosquito-misting.com/life%20cycle.htm

* Flies: http://www.flycontrol.novartis.com/species/housefly/en/life_...

* The young mosquitoes / flies are very different from the adult forms, they have a very different lifestyle and food. But they are nasty so it's better to just ignore them.

* Butterflies: http://questgarden.com/120/22/8/110228062006/process.htm

* Young butterflies live in the wild without protection like the ants/bees equivalent. So they are easy to spot and they are more difficult to relate to the adult forms. They are colorful to hide or as a bad taste signal, so they are nice and many of them have a special name that is unrelated to the name of the adult form. Butterflies in general are colorful and nice too, so we know a lot of names of the species of caterpillars and butterflies.

(You can find more examples in Google, searching for: life cycle <insect> )

So the changes are very common insects, but the case of the caterpillars / butterflies is more surprising because both forms are popular.

(Changes are also common in other kinds of animals / plants /fungus / etc., but this is getting too long, so lets analyze only.)

[robbiep]

I don't know exactly what happens but apparently they mostly turn to mush then reassemble. Interestingly their nervous system/memories have been shown to survive between the different stages.

Re genes turned off: as another poster mentioned huge numbers Of genes are switched off and on at different stages in our life cycle. It's kind of the same as saying 'but neurone don't need the same genes as skin cells so isn't it wasteful having all those extra genes doing nothing?' DNA is relatively cheap so while some 'skin' genes may never Be used in 'neuron' cells the cost is not prohibitive To the organism.

Http://bit.ly/VNYxx2 (a link to livescience.com - apologies am moving between different devices, blocked HN on my mac!)

[polyfractal]

A lot of insects have a fully intact, if immature, nervous system during their adolescence. For example, fruit flies (drosophilla) have brain features called "mushroom bodies". These grow during larval development then hit a state of hibernation until the larva changes into an adult fly, at which point growth continues and the mushroom body fully develops.

I'm not familiar with a lot of other insects, but I believe it is fairly common for the bulk of structures to form, hibernate, and then finish growing during metamorphosis.