We have soft flesh on the outside and hard bone on the inside. Animals like crabs and insects have soft in hte inside,e hard on the outside?
How does that work?
- Ronald 7Lv 710 months ago
It has always been Evolution's method of Armour for protection
Since the Dawn of time
A case of Eat or be Eaten
- Elaine MLv 710 months ago
Insects and crabs aren't mammals.
- ElizabethLv 710 months ago
Let's suppose you built a machine that could double my size. I'd be twice as tall, twice as wide, twice as thick. In other words I'd be 8 times heavier and have 8 times the volume I started with. My skin would have 4 times the surface area.
Small animals have a small volume but quite a large surface area. Their surface area to volume ratio is high. This means that they loose heat quickly to their surroundings, so shells and exoskeletons act as insulators. They also protect the soft squishy innards as you say and prevent the animal drying out.
But exoskeletons can be very complicated. They can be thought of as an organ of the animal. Some animals can excrete waste materials through their shells. In an insect or crab, they are attached to the body and have tendons and muscle fibres connecting the parts allowing them to bend and move. They can be sensitive to touch and heat. In fact, the chemical composition of shells and exoskeletons changes depending on whether certain parts need to be harder or more flexible.
Some shells grow with the animal. Other species shed them and grow new exoskeletons as their body grows. They often pump themselves up so when their shells / exoskeletons harden, they have a bit of growth room before having to do it again. Some of our pesticides work by inhibiting this process and insects suffocate by getting too big for their exoskeleton.
But if these animals get too big then, as in the case of doubling my size, their exoskeletons end up weighing too much. They'd not be able to move because they simply couldn't pack the muscle power over their surface area to compensate for the more rapid increase in volume and weight.
That's why we have an internal skeleton ... it doesn't need to encase our entire surface. Instead our bodies hang around that smaller, lighter endokeleton.
- DixonLv 710 months ago
It is usually to do with some material properties scaling by area (or length) versus other properties scaling by volume. So mostly it works by absolute size, although obviously there is some overlap. It turns out that above a certain size it is not easy to make exoskeletons work - not by the incremental steps of evolution, anyway. For instance, the chitin of insect exoskeletons isn't a strong enough material above a certain size because absolute strength scales with cross section (area) whereas mass scales with volume.
There are also problems scaling certain general morphologies. For instance, insects don't have lungs and they "breathe" through tiny holes in the exoskeleton. And again it turns out that above a certain size this isn't a viable mechanism and you basically need lungs. So insects (which happen to have exoskeletons) are size limited by the need for oxygen, whereas mammals, birds and reptiles don't have this problem because they already have internal lungs.
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- martinLv 710 months ago
It works well for those animals who must worry about giant seals or sharks devouring them. Humans are envying a lot of good defenses animals have by nature.
- Anonymous10 months ago
Arthropods have exoskeleton. we have internal skeleton. That is just how we evolved and how arthropods evolved. Animals often evolve different solutions for the same need or the same problem. Sometimes there is only one way to solve a particular problem, and different animals evolved to be very similar. For example, flying squirrels are more closely related to elephants than they are to sugar gliders (which are more closely related to kangaroos than to squirrels), and yet both have the same type of gliding apparatus, a skin membrane that stretches between their front and rear llimbs. .
- daniel gLv 710 months ago
That hardened chitin skin takes the place of an internal skeletal system, most commonly smaller arthropods. Not that some crustaceans can't get a fair size, or such as a mammal very tiny like a large bumblebee.
No known animal has both, save for nails or talons.
You are talking the difference between vertebrate and invertebrate animals here.
Reptiles can have hard scales for skin even with an internal skeleton.
- 10 months ago
if you are asking how come we don’t have exoskeletons or insects being squishy in the outside then it’s adaptation and natural selection. Assuming we evolved from monkeys they didn’t have exoskeletons so we wouldn’t have them and we got no use for them. But why don’t monkeys have them? Well it’s adapting to the environment of there was any exoskeletal monkeys then it must have been more of a dead weight then a benefit seeing how if there was any how they are extinct today because of natural selection