Why aren't animals more homogenous?

[SFNQuestions]

It seems like most or all animals have a very firm structure of their body followed by a very soft structure of their body, whether it's a bug or a mammal or a snail...but why? What would happen if an animal was moderately soft/hard throughout it's entire body? It seems like having such a body works for an octopus.

[swansont]

It seems like most or all animals have a very firm structure of their body followed by a very soft structure of their body, whether it's a bug or a mammal or a snail...but why? What would happen if an animal was moderately soft/hard throughout it's entire body? It seems like having such a body works for an octopus.

Or a jellyfish. Both of which live in the ocean. They don't have to stand up and move without the buoyant force from water to help them.

[Country Boy]

Actually, an octopus does have a hard bone around its brain- but what SFN said is the best answer

[SFNQuestions]

Or a jellyfish. Both of which live in the ocean. They don't have to stand up and move without the buoyant force from water to help them.

Okay? But there's plenty of terrestrial animals that are light weight, so why aren't those animals more homogeneous? If the tissues compress at a certain point it would eventually create enough of a normal force for something to stay upright.

[CharonY]

To maintain shape a certain level of rigidity is required and mechanically more is required to support larger body sizes. However, when considering octopus as soft, why are snails considered to be different?

 

Edit: or do you mean amorphous?

Edited February 18, 2017 by CharonY

[SFNQuestions]

To maintain shape a certain level of rigidity is required and mechanically more is required to support larger body sizes. However, when considering octopus as soft, why are snails considered to be different?

 

Edit: or do you mean amorphous?

I mean you realize your movement is from your muscles right? A skeleton can't push on anything, cause it has no muscles...If astronauts don't work out into space, it doesn't matter that their skeleton still exists, their muscles will atrophy and they won't be able to walk...because of the loss of muscle tissue. There's a better explanation for the lack of homogeneity somewhere out there seeing as how it's completely plausible that a layer of tissues harder than mammalian skin but softer than arthropod exoskeleton can easily compress enough to maintain an upright form, which already happens to some extent anyway (because if it didn't people would form a puddle of bones whenever they walked).

Edited February 18, 2017 by SFNQuestions

[Moontanman]

Actually, an octopus does have a hard bone around its brain- but what SFN said is the best answer

 

 

Can you supply a link to that assertion? I've kept a lot of octopus in my day and the only thing hard in them is their beak...

[Endy0816]

There's cirrate octopuses with an internal cartilage shell. Might be what he's thinking of.

 

https://en.wikipedia.org/wiki/Cirrina

 

Removed shell:

 

 

 

 

Edited February 19, 2017 by Endy0816

[mistermack]

The answer to the original question is just a matter of evolutionary history.

There were plenty of soft-bodied swimmers in the sea at one time. Some are still around. Look up hagfish and lampreys. And sharks and rays have a less hard, cartilage skeleton.

It just so happens that others evolved bony skeletons. Many also evolved bony armour. Especially in the past.

Most species that ever existed are now extinct. What we have now are the lucky ones, that always found a niche for themselves as they evolved.

The bony fish were the ones that first dragged themselves onto land, and became amphibians. You would think that having a harder skeleton for the fins to lever against helped make locomotion on land more efficient.

But it might be that they just got there first, and got a head start on all of the others, which proved decisive.

 

Animals are the way that they are because their ancestors found ways to survive and resist extinction.

Marine worms are a success in their own way, just as elephants are.

Things don't have to be bony, but in some circumstances, it has been a success. But there is no rule about it.

Hagfish have been more of a success than most bony fish. Because they are still here, and most bony fish species have gone extinct.

[SFNQuestions]

The answer to the original question is just a matter of evolutionary history.

Obviously.

 

There were plenty of soft-bodied swimmers in the sea at one time.

What about the rest of the animal kingdom?

 

It just so happens that others evolved bony skeletons. Many also evolved bony armour. Especially in the past.

This is nothing new.

Edited February 19, 2017 by SFNQuestions

[mistermack]

What makes you think that the true answer to your question should be new and non-obvious?

[SFNQuestions]

What makes you think that the true answer to your question should be new and non-obvious?

The problem isn't that the answer is cohesive, it's that it's so vague that it could be true of anything, it contributes absolutely nothing. Any animal species is exactly the way it is because it evolved that way, there's no other explanation unless you're a creationist.

Edited February 22, 2017 by SFNQuestions

[mistermack]

The problem isn't that the answer is cohesive, it's that it's so vague that it could be true of anything, it contributes absolutely nothing. Any animal species is exactly the way it is because it evolved that way, there's no other explanation unless you're a creationist.

Well, when you ask such a generalised question, you get a generalised answer.

Each species has it's own history, it's own niche and it's own strengths and weaknesses.

If you want to know why there are so many more now, with hard inner skeletons, then it's down to what those skeletons do.

For the most part, it's the obvious answer. They act as levers, enabling more rapid motion, and also give stronger support than just muscle.

You only have to look at your own legs, and picture what they would be like without bones.

 

The answer IS pretty obvious. And always has been. And that's why it's not new.

[SFNQuestions]

Well, when you ask such a generalised question, you get a generalised answer.

Well, when I ask a general question like "why are animals the way they are?", then I'd expect a general answer and I'll come get you. When I ask a specific question like "why do most animals lack this specific attribute?" as I did in this thread, I expect a specific answer.

Edited February 22, 2017 by SFNQuestions

[mistermack]

Well the answer is obvious. There are some advantages to having a skeleton. It seems you don't like the obvious answer, but that doesn't make it wrong.

If you have an idea of some non-obvious answer, why not share it?

 

There are plenty of animals that have more homogeneous bodies. Like grubs maggots and caterpillars. Billions of them. They are suited to their own niches. And have various ways of keeping going, such as being inaccessible, or being poisonous, or having enormous fertility.

They don't survive just on one aspect, such as body form. Nothing does.

 

Evolution works on variety. No single body form dominates. If you go on simple numbers, then grubs, maggots and caterpillars are probably as numerous as other types.

But then they go the other way, with an exoskeleton, if they undergo metamorphism.

The one form is successful in finding food, the other in mobility which helps finding a mate.

[Anthony Morris]

No one is certain why some species have hard parts per se, but there are good reasons for things like shells, bones and exoskeletons. It is believed that early multi-cellular life needed calcium for certain functions and began acquiring it from the sea water around it. Those species that could store some of this calcium survived better in general and became more dominant than others. Later as predators arose and spread, those species that were able to develop shells or carapaces had an evolutionary edge and since calcium sequestration was already commonplace in some lineages these species used the calcium they already had to form their armor. Some species used their calcium to produce internal skeletons that gave their musculature leverage thereby enabling them to swim away from predators and to also pursue prey. As vertebrates explored shallower waters for food and safety, some didn't need to swim quite as much and some species began to develop methods of holding on to their surroundings. Hands, feet, fingers and toes developed. Some of these species then began to make use of the shoreline and then later the shore itself. This required support against the much tougher environment out of the water. Since these animals already had bones, they adapted these for the new environment.

 

Insects evolved their exoskeletons in a similar way ultimately reducing the calcium content in favor of chitin which is lighter and cheaper to make on land.

 

"Squishy" life often manages to survive. Calcium sequestration or storage is not an essential aspect of life but species that do have it have some advantages in a great many habitats.

[SFNQuestions]

They don't survive just on one aspect, such as body form. Nothing does.

 

Evolution works on variety. No single body form dominates. If you go on simple numbers, then grubs, maggots and caterpillars are probably as numerous as other types.

But then they go the other way, with an exoskeleton, if they undergo metamorphism.

The one form is successful in finding food, the other in mobility which helps finding a mate.

Not that that's necessarily true, it's not being debated. Maggots are still arthropods and lose their softness as they age, thus they would not fall into something that would be considered a mean of arthropods and mammals. No one is debating that evolution yields a variety of results. In fact, just the opposite, like why hasn't evolution yielded this one specific result as much as these two other results?

 

Well the answer is obvious.

If the answer is obvious why haven't you answered it?

There are some advantages to having a skeleton.

No one is questioning this.

Well the answer is obvious.

If you have an idea of some non-obvious answer, why not share it?

Because I'm not a biologist, hence I am posing a question to accredited biologists.

[CharonY]

I am still not sure what you really mean. Do you mean why there is so little variety in soft-bodied organisms? There already are several answers to that, including that a) a lot of soft-bodied animals exist (such as annelids, certain molluscs, cnidaria, animals with few or single cells etc.) , but without some for of external or internal body shapes there are, at minimum, mechanical limitations especially outside of water. This issue scales with size. I.e. a very large worm can only grow in length but not too much in girth, otherwise it would be too massive to move. But even at small sizes the ability to move differs significantly. Just compare the movement types found in a variety of annelids and contrast that to e.g. equally sized caterpillars.

[SFNQuestions]

I am still not sure what you really mean. Do you mean why there is so little variety in soft-bodied organisms? There already are several answers to that, including that a) a lot of soft-bodied animals exist (such as annelids, certain molluscs, cnidaria, animals with few or single cells etc.) , but without some for of external or internal body shapes there are, at minimum, mechanical limitations especially outside of water. This issue scales with size. I.e. a very large worm can only grow in length but not too much in girth, otherwise it would be too massive to move. But even at small sizes the ability to move differs significantly. Just compare the movement types found in a variety of annelids and contrast that to e.g. equally sized caterpillars.

Nope, not soft-bodied, intermediate bodied. As I said in the first post, something in between a stiff exoskeleton with a soft inside and a stiff endoskeleton with a soft outside. A reasonable mean between those two would be a moderately rigid/soft organism that has a nearly homogeneous stiffness from the surface to the center. But, I've never heard of an animal like that. I guess maybe cartilaginous fish would qualify for that.

Edited February 24, 2017 by SFNQuestions

[Argent]

Nope, not soft-bodied, intermediate bodied. As I said in the first post, something in between a stiff exoskeleton with a soft inside and a stiff endoskeleton with a soft outside. A reasonable mean between those two would be a moderately rigid/soft organism that has a nearly homogeneous stiffness from the surface to the center. But, I've never heard of an animal like that. I guess maybe cartilaginous fish would qualify for that.

Put in overly simplified terms, material that was squidgy is unlikely to perform well as both a support structure and the body's organs. It's the same reason we don't make the engine and the upholstery of a car out of the same substance.

[Bender]

Indeed, the motor itself needs to run smoothly, otherwise you loose too much energy moving the motor. The motor needs to be supported by a strong frame, otherwise it will deform the frame rather than move the car.

 

Same holds true for animals: stiff muscles are too stiff to move themselves and weak bones cannot support the forces. Just look at squishy animals such as worms and snails: they are usually small and slow, both in water and on dry land.

[SFNQuestions]

Put in overly simplified terms, material that was squidgy is unlikely to perform well as both a support structure and the body's organs. It's the same reason we don't make the engine and the upholstery of a car out of the same substance.

I don't think that's an appropriate analogy because if there was in fact a metal that could withstand heat and was light and was very hard and electrically conductive and economically inexpensive, they would actually manufacture most components out of that substance. There are many many varying circumstances in a car that require specialized substances, and science has yet to discover a material that can address that variance all at once.

[Argent]

I don't think that's an appropriate analogy because if there was in fact a metal that could withstand heat and was light and was very hard and electrically conductive and economically inexpensive, they would actually manufacture most components out of that substance. There are many many varying circumstances in a car that require specialized substances, and science has yet to discover a material that can address that variance all at once.

I suggest it is an excellent analogy. If I may adapt your own writing to support my argument:

 

There are many many varying circumstances in the body of an animal that require specialized substances, and nature, despite over three billion years of evolution by natural selection, has yet to discover a material that can address that variance all at once.

[SFNQuestions]

I suggest it is an excellent analogy. If I may adapt your own writing to support my argument:

 

There are many many varying circumstances in the body of an animal that require specialized substances, and nature, despite over three billion years of evolution by natural selection, has yet to discover a material that can address that variance all at once.

The problem is that you don't actually know that nature didn't discover it already. And furthermore, the structure doesn't have to provide all the functionality of an organism like it would in a car, just the homogeneous stiffness.

[Argent]

The problem is that you don't actually know that nature didn't discover it already. And furthermore, the structure doesn't have to provide all the functionality of an organism like it would in a car, just the homogeneous stiffness.

If nature has already discovered it, where is it? I would never rule out the possibility the animal may be hiding somewhere, but I would regard it as highly improbable. Your own view, expressed in the opening post, was "It seems like most or all animals have a very firm structure of their body followed by a very soft structure of their body, whether it's a bug or a mammal or a snail". Now you are suggesting that your impression was faulty. I cannot follow your logic.

 

The requisite degree of stiffness would seem to preclude the necessary flexibility for organs, muscles etc. You are proposing a uniform "consistency". You need to demonstrate that organs and muscles could function effectively if sufficiently "stiff" to work as a skeleton. The car analogy stands. We don't build cars that way. Nature does not build land animals that way.*

 

*(I have understood you to use animal to mean vertebrates. If you don't mean vertebrates, then there are plenty of land dwelling creatures that are fairly homogenous in terms of "stiffness" throughout. Worms and snails come immediately to mind.)