In terms of phsyics/chemistry rather than natural selection, how do some animals have exoskeletons while our skeletons are internal?
- Anonymous5 months ago
An organism can only inherit and modify what its ancestor has genetically. If the body parts that an animal has inherited makes it more likely to have an external skeleton then it is what is likely to evolve.
Originally, fish evolved an external skeleton of hard plates. They are called placoderms. Other fishes, including living ones, evolved from placoderms. Therefore it would appear that the physics favored the change from exoskeletons to internal skeletons, perhaps because a fish without exterior protective plates can swim faster. Eventually the placoderms became extinct, and they have been replaced by soft-bodies fishes with internal skeletons.
- busterwasmycatLv 75 months ago
skeletal structures or whatever word you want to use for mineralized body parts are produced by specialized cells. The location in the body of those cells dictates where the mineralization will happen. It is basically a case of supersaturation of the system with respect to the mineral product as induced by the cell activities. Cannot really discuss the where except in terms of evolution, though, because natural selection is what does the winnowing between "successful" and "unsuccessful" body models or structure.
- ZirpLv 75 months ago
Some animals have DNA for an exoskeleton, some have DNA for an internal skeleton
- JulienLv 75 months ago
We could say that animals with exoskeletons are usually tiny. Tiny things are typically more robust, because chemistry introduces a typical scale which breaks the scaling invariance (so that things such as Young's modulus are dimensional). So it could probably be argued that large-sized exoskeletons would not be viable, it would not be hard enough compared to the magnitude of the physical constraints on such a large body.
Then you still need to invoke evolution to explain why some small animals have an endoskeleton (because they evolved from a larger one) and some relatively big animals have an exoskeleton (because they evolved from a smaller one).
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- JazSincLv 75 months ago
It's an evolutionary history thing.
We're not descended from armored worms.
We're descended from neotenous echinoderm larvae.
- Anonymous5 months ago
Those animals with exoskeleton also have endoskeleton. They've just started to grow the same material made out of bones on the outer part of their body in addition to the ones inside them, because it helps protect them from external harm.