http://www.straightdope.com/columns/read/2829/ok-why-exactly-does-a-caterpillar-morph-into-a-butterfly
Ok, for this explanation, it’s not possible. Evolution isn’t a designer, it can’t make plans about what it will be able to optimize. The metamorphosis has to have a benefit right away. Also, it has to have a benefit that will work a little at a time, so it can’t think, “If I do this I’ll be able to make a cocoon eventually, if I get started right now.” So it was probably evolving the ability to make silk, or whatever it’s made of, I don’t know, for some other reason. Then it would have gained the instinct to make a cocoon and stay in it during its metamorphosis, where it will be safest. Then the silk would probably be optimized to be cocoon material, and the metamorphosis would become even more drastic than before, since the larva can easily survive inside the cocoon, whereas before this would be a problem. So that’s what could have happened, but I really have no idea.
You might find this article interesting. There are intermediate forms of metamorphosis called incomplete metamorphosis that represent steps along teh way to complete metamorphosis.
The details are here:
Well, very loosely speaking, OP is right. Evolution happens in tiny steps, where every little tiny increment generally has to have some incremental survival value.
It was a standard argument of the Intelligent Design folks to claim that an eyeball can’t do its function until it’s entirely evolved that that this couldn’t have happened by mere random mutations. There had to be a Designer. The rebuttal is to argue how an eyeball could have developed in tiny increments, all of which had some survival value. For example, the simple one-cell critter Euglena has a reddish “eyespot” that appears to function as a primitive light filter, enabling the critter to orient itself toward light. I read somewhere, some example ideas of incremental evolutions that could have taken it from there to a fully developed eye. For example, at some point, a layer of clear gel-like protein could have formed over the eyespot, perhaps concentrating a little more light, forming a primitive lens.
So, one might presume, the evolution of complete metamorphosis might have happened in tiny increments each having some incremental survival value, as OP suggests.
ETA: The Wiki article Evolution of the Eye contains a section outlining a theory of the stages of eyeball evolution.
The book In the Blink of An Eye is a lay-accessible presentation of Andrew Parker’s “light switch” theory of eye (and other) evolution referenced in the Wiki. I found it an interesting read.
I don’t think all mutations need to have a greedy benefit within the next one or two generations. While not as large-scale as evolution, I work with stochastic processes that, roughly, compete to survive all the time. They still pick up some weird, weird crap as long as it’s not actively detrimental to the result.
It seems entirely reasonable that some things can evolve “just because”, in that they were incidental traits that just so happened to be carried by individuals with actual beneficial traits. Then those prototype traits eventually became refined into actual beneficial, selective traits themselves once they were far enough along to meaningfully affect survival with only a few small mutations.
I think you misunderstood Doug. Metamorphosis is a process that developed over time, with older insect forms not having it, or having incomplete forms. What Doug was saying is that changes in the life cycle of certain insects created transition stages, and the effect of stages was to allow natural selection to work on each stage independently.
He didn’t speak to the specifics of what drove the development of those stages.
The linked article gives some better guesses on that.
One thing that genuinely has been puzzling me regarding evolution is that mutations can occur from one generation to the next, and are in all cases I’ve read of “purposive”. It is as if the organism thought, “Hey, this would be handy”, and then strive to that end over thousands of years, or from one generation to another (without any God involved, mind you).
For instance, lizards that evolve from one generation to another both in longer limbs and new innate behavior when exposed to fire ants. The mutation is not random, but obviously seems to have an end – some kind of “idea” that the organism follows, as it were.
I read recently (in a Swedish magazine, Illustrerad Vetenskap, 4/2015) of another lizard that transformed from one generation to another; when their environment was invaded by another species, they got sticky feet that made it possible to move to and inhabit another area. So the mutation is a purposive reaction of something that happens to one generation of lizard, in these cases at least.
Studies has also been done on plants vs. insects, where plants that are exposed to certain insects mutates into being more poisonous very fast; while the same plant in another area with less insects do not mutate (Swedish newspaper Svenska Dagbladet, which refers to Science, but there seems to be no link in the article to the original source any longer.)
If Wikipedia describes it thoroughly, I can get these examples to fit in the evolution theory. But there’s probably ignorance to be fought here, so… any help appreciated.
EDIT outside edit window: In the last paragraph it should of course read “I can’t get”, rather than “can”.
Edit never mind
This is not a case of a mutation ocurring in one generation. First off, it is comparing population groups within a species that have a different environmental pressure (ie fire ants), the exposed group having 60 years of exposure. That’s a lot of generations of lizards.
Second, this is not a mutation, this is a shift in gene frequency. The population of lizards had members with short legs and some with longer legs. Without fireants, there is no selection pressure (ie survival advantage) for the longer legs. Once the fireants arrived, that created a selection pressure, so the lizards with longer legs reproduced more, and their young carried the longer leg genes, and they reproduced more, etc.
Same thing for the behavioral trait of shaking and leaving. All the young lizards do that, because they are at more risk from ants. Adult lizards were safer from ants because of their scales, until fireants. Ergo, they become more skittish. The question still remains if that is a learned trait.
I can’t speak directly to your other examples.
With regards to caterpillar and butterflies and how it might evolve, consider the dramatic changes for marsupials like kangaroos. Their early development is almost entirely spent on the front half of the body, the head and arms. While still a tiny fetus, the half-formed joey crawls from the vaginal opening to the pouch on the belly to attach to a nipple. The it transforms from a peanut-sized pink fleshy nub to the fully formed Joey that can leave the pouch.
That creates two different environments for the development of marsupial mammals, where traditional mammals do all their development in one environment.
Or the human approach to early birth and more helpless infancy to offset increased cranial size. Two environments, but no need for the specialized stages of marsupials.
Thank you, Irishman, that clarifies it a bit!
Because if it morphed into a steam shovel, it would be a Transformer.
It could still be a Caterpillar, of course…
Caterpillars aren’t a species that once upon a time started the process of evolving into butterflies (unless you count going WAY back to some proto-arthropod similar to velvet worms). Almost certainly it was the other way around: some insects evolved/reverted to having a larval stage because it was advantageous.
Insects are among the most widespread and successful group of animals, and that’s probably because they evolved flight. Flight is a great way to cover far more territory than a land-bound species can. But on the other hand there are food opportunities that either don’t require flight or would be obstructed by it. Hence the metamorphic life cycle. The larval stage eats and grows, then the adult stage flies to mate and disperse its eggs. Some insects like mayflies don’t even bother to eat as adults.