Evolution or de-volution ?

I just read a thread about what came first. The chicken or the egg.

This made me wonder about evolution.
A lot of people say that once an evolution step is made it can't be reversed.

Like dolphins. They returned to the ocean after they evolved to be a land dwelling mammal. There gills have turned into something else so they now have to resurface to take a breath using their lungs.

It's said the first land animals got grounded to lay their eggs. For safety reasons.
This meant the egg had to develop a protective shield.

Now for my question.
How did mammals got in reverse, threw away the egg shell and started to lay shell less eggs. Protected by their own body instead.

Does anybody knows this or maybe knows where I have to look to find out ?
One mammal still lays eggs ??? The Platypus.

Any thoughts ?

It's both, whatever is necessary. Either it grows and transcends itself or it will break apart into it's constituent parts. As I learned it from Ken Wilbers Holism.

Holism and Ken Wilber

reply to post by damwel


Please, do not feed people your pseudoscience/philosophy. This question can be answered with science, just as the poster is asking for.

reply to post by Sinter Klaas


Mammals evolved from reptiles, and therefore, early mammals layed eggs. The 5 egg laying mammals today (monotremes) have retained egg laying through their evolutionary history. Live birth came about because it was an adaptive trait, and all other mammals exhibit this. There are species of snakes and shark that give live birth as well, so it's obviously favorable for some species in their environments.

I've never heard anyone say that evolutionary "steps" cannot be reversed, though that idea is probably a misconception to begin with.

Like dolphins. They returned to the ocean after they evolved to be a land dwelling mammal. There gills have turned into something else so they now have to resurface to take a breath using their lungs.

wtf!!

got a credible source, for that?!?(pls not wiki) i find that remarkable if true.

I personally don't think that it's going backwards (is there such a thing as devolution) for baby's to be born live, instead of fragile, and vulnerable eggs.

I don't think we devolve, we only evolve further. and with the advanced world i think that people are doing it much slower than we used to. you don't need to outrun many tigers these days.

If we are evolving still, then it's probably in tune with the modern world, like finger dexterity. bum cushioning, and shoe selecting abilities.

I always thought the answer to the "What comes first? The chicken or the egg" answer - thought came first. but I think in reverse alot so that could be wrong.

I would just like to make it clear that there is no such thing as de-evolution. For something to devlolve it would mean that there is a specific goal to evolution, which there isn't. Evolution is simply the change in inherited traits across generations. So, if a species has one trait, gains a new one that replaces it, and then goes back to the original trait, it is still evolution because it is still a change in traits between generations.

Originally posted by PieKeeper


reply to post by Sinter Klaas

 

Mammals evolved from reptiles, and therefore, early mammals layed eggs. The 5 egg laying mammals today (monotremes) have retained egg laying through their evolutionary history. Live birth came about because it was an adaptive trait, and all other mammals exhibit this. There are species of snakes and shark that give live birth as well, so it's obviously favorable for some species in their environments.

I've never heard anyone say that evolutionary "steps" cannot be reversed, though that idea is probably a misconception to begin with.

I learned the first land dwellers were ....don.
They were also the first ones that were victim of a mass extinction. With this event dinosaur got it's chance to re-populate the Earth.

These ...dons were more like modern day mammals like dinosoars were. They survived as subteranian creatures only to regain there place as dominant branch after the dinosaurs got extinct.

reply to post by Xcalibur254


I'd like to explain myself using the dolphin example.

The gills were eventually changed into a new function. ( something with jaw muscles.Not sure )
So this means this new development has to un develop to become gills again. This doesn't happen because they still get used.

devolution was the only thing I could make up to explain myself.

Like a mole losing their eye side because they don't use it.
If you have an example of a new ability I would appreciate it ?

reply to post by MR BOB


Where can I start.

My knowledge in this matter comes from watching discovery, national geographic channel, animal planet and biology class and reading science news ( a lot ). And reading alot of articles published by those who study and teach it.

I can't really give you just one or even 10 sources.

Edit.
If you insist I could look it up for you.

Human babies are in fact born premature. That's why they need constant attention. With other species offspring it's common it can survive alone or at least can get around on it's own.



[edit on 15-4-2010 by Sinter Klaas]

reply to post by damwel


I'm still going to look in to that.

reply to post by Sinter Klaas

Now for my question. How did mammals got in reverse, threw away the egg shell and started to lay shell less eggs. Protected by their own body instead.

Simple answer is, they didn't.

Mammals don't lay eggs without shells. Those mammals that still lay eggs, lay them with shells, though they are not calcified like a bird, they are more 'leathered' like a reptile.

But most mammals don't lay eggs, and the hard shell simply isn't needed, so it evolved into something less recognizable as a shell and more useful to the embryo developing in the womb: the placenta.

It is said that organisms don't "devolve" even though they may lose and regain certain features many times. Think of it as a wall that is painted blue but you don't like blue so you paint it green, your favorite color. Your wife comes home and hits the roof because she hates green. So you do the responsible thing, explain why it should stay green, and then repaint it blue.

Notice that you don't 'devolve' the wall back to blue by removing the green. Your wall just goes through another evolution event that happens to end up where it was in the first place. Each change is in response to some environmental pressure that selects for the best result.

reply to post by rnaa


Hi thank you for your answer. However it was not the one I was looking for. ( no offense )

I used the dolphin example to for a reason.
That reason was their lungs. Why didn't they simply evolved gills again.?

Well... It seems that the muscles that powered the gills are used in mammals to power the jaw.

My understanding is that every egg has a shell. Ours just look more like frogs or fish because of the moist surrounding it is developing in.

The placenta is the equivalent of the egg yoke. ( Yellow in the midst of all the white in a bird egg ) Wasn't sure how to translate and spell it correct...

reply to post by Sinter Klaas

Hi thank you for your answer. However it was not the one I was looking for. ( no offense )

Sorry. I didn't realize you were asking a question to which you already knew the answer. I thought you were trying to understand why organisms don't 'devolve'.

My answer is in the 'paint the wall' analogy. What is your answer?

I used the dolphin example to for a reason.
That reason was their lungs. Why didn't they simply evolved gills again.?

Well... It seems that the muscles that powered the gills are used in mammals to power the jaw.

Sharks have both gills and jaws. And their jaws are much more powerful than the dolphin's.

So while your gills to jaw muscle assertion may (or may not, I haven't researched it) be correct, it is not necessarily the 'simple' reason.

The real reason is that they had a perfectly useful and more efficient, method of oxygenation: the lungs, so they didn't need to 'devolve' to using gills. They had something better that they could make to work by 'simply' relocating their nose to the top of their head.

So to go back to my 'painting the wall' analogy. When your wife complains about your color choice, you don't repaint it blue, you repaint it olive which, while still a kind of green which you like, is more to your wifes liking than the forest green you painted it in the first place. But you don't 'devolve' by scrubbing the green off to get back to the blue.

Likewise organisms don't devolve, they evolve to something new, which may be very similar to something they used to have, or not.

My understanding is that every egg has a shell. Ours just look more like frogs or fish because of the moist surrounding it is developing in.

Every egg has an outer membrane of some sort, certainly. Not necessarily a 'shell' however. Birds are calcified and that's what most people think of when they talk of an eggshell, but reptile eggshells are more 'leathery' than hard. Frogs and fish don't have hardened shells of any kind.

At least some marsupials form 'leathery' eggshells internally, but the shell is re-absorbed before the live birth. I can't find any indication that this is the case for any other live birth mammal.

The placenta is the equivalent of the egg yoke. ( Yellow in the midst of all the white in a bird egg ) Wasn't sure how to translate and spell it correct...

Yeah, sort of. I stand corrected.

I guess we could quibble about it. I think the placenta more the equivalent of the inner membrane of an egg though. The umbilical cord is more the 'replacement' for the yolk.

reply to post by rnaa

I'm sorry my response is a bit late.
Sorry. I didn't realize you were asking a question to which you already knew the answer.

I'm sorry what are you doing ? I would not ask a question if I new the answer. Your answer was not the answer I was looking for.

My answer is in the 'paint the wall' analogy. What is your answer?

You really brake my balls here.

Sharks have both gills and jaws. And their jaws are much more powerful than the dolphin's.

Well... Probably because a shark never lost it's gills.

The real reason is that they had a perfectly useful and more efficient, method of oxygenation:

I disagree. You can't be serious saying this. Please don't answer a question if you don't know the answer yourself or mention it's a wild guess or something.

Likewise organisms don't devolve, they evolve to something new, which may be very similar to something they used to have, or not.

Give me one example of something new.

It's obvious you didn't study these things. Why then, do you answer ?

I must apologize. I assumed my example was common knowledge.

Originally posted by Sinter Klaas
reply to post by rnaa

 

I used the dolphin example to for a reason.
That reason was their lungs. Why didn't they simply evolved gills again.?

The problem is the dolphin and whale did not devolve back into the water, They adapted to there surrounding of the time(Evolved).

It is really that simple. (if I am understanding your question correctly)

"evolution step is made it can't be reversed." This comes from Dollo's Law of Irreversibility.
en.wikipedia.org...


books.google.ca...=onepage&q&f=false

[edit on 22-4-2010 by nophun]

reply to post by nophun


Hi thank you for your reply.

About dolphins...

These marine creatures were once land based animals. At a certain point in time these animals were drawn back into the oceans.
Food or shelter or maybe because of a elevating sea level. They were at that able to adept.

Do you know that the closest land animal of a dolphin is a hippopotamus ?
Food or rising seas are less of a boundary to it then to any other land animal alive. But did they evolve anything new to make them more fit to their situation ?

No.
Basically the still have the same features as any mammal.
They did loose their legs. Like a moll lost it's eye side. or anything.

What keeps happening is that certain parts adept ( not turn into something new. And certain parts they just loose.

You say and I now it is understand as truth that new developments can't be un-done. Like the lungs in a dolphin.
Yet they lost their legs what were once fins on a fish.

My question about us and the eggs women produce.
Those eggs are more or less the same as they were while we only lived in the sea.. They lost the need and thus ability to have a hard shell. But it is not a new thing.

Any thoughts ?

reply to post by Sinter Klaas


you know I can't really supply you with an anwser, but you do bring forth a pretty good question. I do have a theory for you though, if you don't mind me puttin it out there, but what if have that blowhole is actually more functional then going back to gills. Maybe having that blowhole keeps them more adaptable to there enviorment, because instead of gaining gills again, something happening and them having to try to obtain lungs again, in time to get back to land; what I'm saying is it might have just been easier and more convienent for nature tp keep them with lungs then to switch it over to gills...What it makes me think of though, is how come they didn't adapt to having both lungs and gills like an amphibian?

reply to post by agentofchaos


Well the mucsles that use to power the gills are no longer available and there legs are gone and on land they get beaten buy a seal.

So no gills and a whole new system is also out of the question. Because it can only adept what it has.

For any marine animal not able to breath under water this means. Extra danger with giving birth. The danger of drowning.

An amphibian never lost it's lungs or it's gills.

Thank you for sharing

You say and I now it is understand as truth that new developments can't be un-done.

This was not my intention, Honestly I think you have better understanding on evolution then most. This is kind of why I am not quick to answer, I do not really understand what or why you are asking ?

I am guessing you know of or at least read the link I posted on Dollo's Law.
The second link I posted was to Richard Dawkins book "The Blind Watchmaker" (pg94) witch I think gives a good understanding of what Dollo's Law is and means. (2nd paragraph).

books.google.ca...

My question about us and the eggs women produce.
Those eggs are more or less the same as they were while we only lived in the sea.. They lost the need and thus ability to have a hard shell. But it is not a new thing.

I am not understanding. There was no devolution here.
Your right there is nothing really new in Birds, Reptiles, or Mammals (amniotes) it is all pretty much the same idea done different ways.

en.wikipedia.org...
www.ucmp.berkeley.edu...

There is no regression here that I can see ? Maybe I am missing something.