What made us live in a house?

[gluadys]

Environment changed back and forth, sometime in cycles. It happened in both short and long term. Do we see evolution make lives change in a similar pattern? How does a "back and forth" type of evolution look like?

Yes, we do see "back and forth" evolution when it is evolution within a single species. The frequency of black coloration in pepper moths went up and then down again as the soot pollution around industrialized cities changed. The size of beaks on Galapagos finches moved to larger and back to smaller depending on whether the previous season had been drought or rainy. In another experiment the number and size of colour flashes on male guppies (which female guppies find attractive) went up in a safe environment but down in an environment with predators.

In each of these cases, though, we are dealing with a single characteristic in a single species over a short term.

Such back-and-forth evolution is not possible in the case of two species who have been separated for quite awhile and differ in more than one or two characteristics. Once the populations become separated, there is no way the changes that occur in one species can be shared with the other. So early humans were not able to share with chimps such changes as bipedalism, loss of hair, a fused chromosome, etc. Nor were chimps able to share their new genes with early humans. So the two groups naturally became more different from each other over time as each group accumulated more mutations which were not shared with the other group.

This is called "divergence" and it is a prediction of the theory of evolution. We expect a consequence of speciation will be greater divergence between groups that were once the same, and an overall increase in bio-diversity as they adapt to different ways of living.

 

[Mallon]

How does a "back and forth" type of evolution look like?

In the fossil record, it looks like stasis. Hence Punctuated Equilibrium.

 

[Willtor]

Then why do we build house, but chimps do not? Is that a significant change?

That is probably not a very significant change. I don't know for certain, but that probably isn't even its own change. There probably aren't genes for "build a house" like there are genes for "build a dam" in beavers. Building houses (I suspect) is an exercise in resourcefulness that comes from places where it is necessary. It might be in that very large category of intellectual feats that are made possible by opposable thumbs and a large brain.

 

[juvenissun]

Yes, we do see "back and forth" evolution when it is evolution within a single species. The frequency of black coloration in pepper moths went up and then down again as the soot pollution around industrialized cities changed. The size of beaks on Galapagos finches moved to larger and back to smaller depending on whether the previous season had been drought or rainy. In another experiment the number and size of colour flashes on male guppies (which female guppies find attractive) went up in a safe environment but down in an environment with predators.

In each of these cases, though, we are dealing with a single characteristic in a single species over a short term.

Such back-and-forth evolution is not possible in the case of two species who have been separated for quite awhile and differ in more than one or two characteristics. Once the populations become separated, there is no way the changes that occur in one species can be shared with the other. So early humans were not able to share with chimps such changes as bipedalism, loss of hair, a fused chromosome, etc. Nor were chimps able to share their new genes with early humans. So the two groups naturally became more different from each other over time as each group accumulated more mutations which were not shared with the other group.

This is called "divergence" and it is a prediction of the theory of evolution. We expect a consequence of speciation will be greater divergence between groups that were once the same, and an overall increase in bio-diversity as they adapt to different ways of living.

I understand the short term feature of divergence. The time scale for short term may be, say, 20 million years. However, if given 100 million years, we should see these so-called "divergence" feature is not really divergent. Some of the evolution characters should be discovered as "re-appearing" or even "recycling". I don't mean the same species will come back alive since the last extinction, but some characteristic functions in some species should be discovered in resonance with the environmental change.

So far, I don't think any characteristic biological functions discovered in paleontology show any correlation with cyclic or repetitive environmental change. In other words, the trend of long term evolution is totally disconnected with the trend of environmental change. For example: we do not see any fish species of cretaceous age evolved to an unique cretaceous amphibian. Why should fish become amphibian ONLY in Devonian (?) time, but not in other period of time?

 

[juvenissun]

In the fossil record, it looks like stasis. Hence Punctuated Equilibrium.

If so, why not a whole bunch of new amphibians, or reptiles "reappeared" after the Cretaceous extinction? What was the environmental differences between the post cretaceous extinction and the post permian extinction, so that the newly appeared species were very different in nature?

 

[juvenissun]

That is probably not a very significant change. I don't know for certain, but that probably isn't even its own change. There probably aren't genes for "build a house" like there are genes for "build a dam" in beavers. Building houses (I suspect) is an exercise in resourcefulness that comes from places where it is necessary. It might be in that very large category of intellectual feats that are made possible by opposable thumbs and a large brain.

I think there should be a gene which make a beaver to build a dam. If we switch that gene off, then it will not do it again. I also suspect that there is a (or a few) gene which controls human intelligence. Anybody knows the gene analysis of any of those famous autistic savant?

 

[Mallon]

What was the environmental differences between the post cretaceous extinction and the post permian extinction

A geology professor should know that, juvie.

 

[gluadys]

I understand the short term feature of divergence. The time scale for short term may be, say, 20 million years. However, if given 100 million years, we should see these so-called "divergence" feature is not really divergent.

Why? Divergence is like a watershed. You can have two rivers originating only a few miles apart in a mountain range, but one will head east and the other west. They don't get to reverse their motion and meet each other again.

Some of the evolution characters should be discovered as "re-appearing" or even "recycling". I don't mean the same species will come back alive since the last extinction, but some characteristic functions in some species should be discovered in resonance with the environmental change.

Well, that we do see. When the dinosaurs went extinct, mammals developed to fill the same ecological niches: herbivores, carnivores, sea mammals replacing extinct sea reptiles, etc. We also see it within mammalian orders themselves. When there were no placental mammals in South America or Australia, marsupials developed into forms similar to those the placentals did in Eurasia and North America. So you had marsupial "wolves" and "tigers" and "bears". We have old world and new world monkeys, a South American llama and an Asian camel. We have similar but not identical large flightless birds like ostrich and emu. And let's not forget that some of the Galapagos finches had evolved so far from the standard finch type that Darwin took them for warblers or larks until an ornithologist straightened him out. There is a fair bit of convergence if you look for it.

For example: we do not see any fish species of cretaceous age evolved to an unique cretaceous amphibian. Why should fish become amphibian ONLY in Devonian (?) time, but not in other period of time?

You really have to get the idea of divergence into your mind, juvie. And cladistic speciaton and the nested hierarchy. What happened in the Devonian is that fish split up into different types, teleost and sarcopterygian. Amphibians come from the sarcopterygian branch. But most fish in the Cretaceous -- like most fish today -- are teleost. You do get teleost species of fish that can spend a fair bit of time out of the water (check out mudskippers), so they act a bit like amphibians, but they can't BE amphibians any more than mammals who took over vacated dinosaur ecological niches could BE dinosaurs.

Also, they would have a hard time filling the amphibian niche, because amphibians already fill that niche. (Now we have heard a lot about amphibian populations declining due to pollution. If it happened that amphibians became extinct, then in a few hundred million years you might see some genuine teleost versions of "amphibians" replacing them. But unlike the amphibians we have, which have sarcopterygian features, these would still be teleosts. That is, they would be a teleost cognate of amphibians in the way a marsupial species is a cognate of a placental wolf or bear.)

 

[juvenissun]

A geology professor should know that, juvie.

I don't see much difference, in fact.

Even the exact mechanism is still in debate, but I can see both extinctions were caused by excessive heat in the earth's surface environment. So, after the event(s), the earth surface was cooling down in both cases. And the whole extinction process was pretty fast. The environment was essentially restored back very quickly to what it was before the extinction.

With this understanding, I am a little bit amazed that the dramatic event(s) that caused the extinction was not able to shift the earth's environment off the track, which, I think, is controlled by the astronomical factors, and the subtle, but continuous process of the earth's interior.

 

[juvenissun]

Why? Divergence is like a watershed. You can have two rivers originating only a few miles apart in a mountain range, but one will head east and the other west. They don't get to reverse their motion and meet each other again.

Well, that we do see. When the dinosaurs went extinct, mammals developed to fill the same ecological niches: herbivores, carnivores, sea mammals replacing extinct sea reptiles, etc. We also see it within mammalian orders themselves. When there were no placental mammals in South America or Australia, marsupials developed into forms similar to those the placentals did in Eurasia and North America. So you had marsupial "wolves" and "tigers" and "bears". We have old world and new world monkeys, a South American llama and an Asian camel. We have similar but not identical large flightless birds like ostrich and emu. And let's not forget that some of the Galapagos finches had evolved so far from the standard finch type that Darwin took them for warblers or larks until an ornithologist straightened him out. There is a fair bit of convergence if you look for it.

You really have to get the idea of divergence into your mind, juvie. And cladistic speciaton and the nested hierarchy. What happened in the Devonian is that fish split up into different types, teleost and sarcopterygian. Amphibians come from the sarcopterygian branch. But most fish in the Cretaceous -- like most fish today -- are teleost. You do get teleost species of fish that can spend a fair bit of time out of the water (check out mudskippers), so they act a bit like amphibians, but they can't BE amphibians any more than mammals who took over vacated dinosaur ecological niches could BE dinosaurs.

Also, they would have a hard time filling the amphibian niche, because amphibians already fill that niche. (Now we have heard a lot about amphibian populations declining due to pollution. If it happened that amphibians became extinct, then in a few hundred million years you might see some genuine teleost versions of "amphibians" replacing them. But unlike the amphibians we have, which have sarcopterygian features, these would still be teleosts. That is, they would be a teleost cognate of amphibians in the way a marsupial species is a cognate of a placental wolf or bear.)

Good argument. Due to the non-existence of my paleontology database, I need to pause for a moment.

OK, here is one: fish came up to land in Devonian time. Then from Devonian to Permian, amphibian dominated the land. Then most of the amphibians were wiped out in the late Permian extinction. Now, given the time of Mesozoic era, why don't we see any amphibian species directly evolved from fish "again"?

 

[gluadys]

Good argument. Due to the non-existence of my paleontology database, I need to pause for a moment.

OK, here is one: fish came up to land in Devonian time. Then from Devonian to Permian, amphibian dominated the land. Then most of the amphibians were wiped out in the late Permian extinction. Now, given the time of Mesozoic era, why don't we see any amphibian species directly evolved from fish "again"?

First, although environmental factors set the terms of natural selection, they don't determine what variations emerge in species. So one possibility is that the type of variation conducive to a new invasion of land simply didn't happen.

Also, it is not helpful to use a term like "fish" which covers a whole range of species that were not ancestral to amphibians. Even within the sub-set of sarcopterygians, there were many more sarcopterygians who were not ancestors of amphibians than those which were. Evolution is not something that happens to large groups like fish or sarcopterygians. It happens to species and only to species. And each species--even when closely related to others--will have its own unique evolutionary history. It makes no more sense to say that because species X and species Y are both fish, species X should evolve into an amphibian because species Y did millions of years earlier. Species X and species Y took different forks in the road many generations ago.

One of the things we learned when living coelacanths were found is that they are now a deep-water fish. Maybe they always were, but the evidence is that the sarcopterygian ancestors of amphibians were not. They lived in or near fresh-water streams in fairly shallow water. So there is quite a small number of species that are possible "fish" ancestors of amphibians. All other groups of fish, including other sarcopterygians, diverged from the branch that led to amphibians. So where would new ancestors of a new wave of "amphibians" come from?

Even if other "fish" species developed into terrestrial animals, those animals could not be true amphibians. At best some cognate species that converged on a similar life-style and form.

Then, to get back to the environment again, remember the Permian extinction did not just affect terrestrial animals. A lot of marine life was lost too. So there were plenty of empty niches in the oceans and lakes and streams for post-Permian fish to fill without taking to land. Furthermore, there were still some amphibians on land, and also by this time, reptiles. So they wouldn't have had the predator-free environment the Devonian amphibians did.

So there are plenty of reasons a new invasion of land would not be favored even if the necessary variations turned up.

 

[juvenissun]

First, although environmental factors set the terms of natural selection, they don't determine what variations emerge in species. So one possibility is that the type of variation conducive to a new invasion of land simply didn't happen.

Also, it is not helpful to use a term like "fish" which covers a whole range of species that were not ancestral to amphibians. Even within the sub-set of sarcopterygians, there were many more sarcopterygians who were not ancestors of amphibians than those which were. Evolution is not something that happens to large groups like fish or sarcopterygians. It happens to species and only to species. And each species--even when closely related to others--will have its own unique evolutionary history. It makes no more sense to say that because species X and species Y are both fish, species X should evolve into an amphibian because species Y did millions of years earlier. Species X and species Y took different forks in the road many generations ago.

One of the things we learned when living coelacanths were found is that they are now a deep-water fish. Maybe they always were, but the evidence is that the sarcopterygian ancestors of amphibians were not. They lived in or near fresh-water streams in fairly shallow water. So there is quite a small number of species that are possible "fish" ancestors of amphibians. All other groups of fish, including other sarcopterygians, diverged from the branch that led to amphibians. So where would new ancestors of a new wave of "amphibians" come from?

Even if other "fish" species developed into terrestrial animals, those animals could not be true amphibians. At best some cognate species that converged on a similar life-style and form.

Then, to get back to the environment again, remember the Permian extinction did not just affect terrestrial animals. A lot of marine life was lost too. So there were plenty of empty niches in the oceans and lakes and streams for post-Permian fish to fill without taking to land. Furthermore, there were still some amphibians on land, and also by this time, reptiles. So they wouldn't have had the predator-free environment the Devonian amphibians did.

So there are plenty of reasons a new invasion of land would not be favored even if the necessary variations turned up.

I used the word fish, because I do not know the classification of fishes.

There are(?) some fishes today that they can breath in air. Do you think they have chance to evolve into land animals given a few more million years of time? I would think the chance is very high, consider all factors.

 

[Assyrian]

All the factors? What about cats and dogs and rats that have been at the game a lot longer and like a nice bit of fish waddling out of the water to meet them?

 

[Mallon]

There are(?) some fishes today that they can breath in air. Do you think they have chance to evolve into land animals given a few more million years of time? I would think the chance is very high, consider all factors.

So... you adamantly reject evolution to the point of calling its subscribers "stupid", yet you think it is high likely that air-breathing fish like mudskippers and lungfish could evolve to become terrestrial animals?

 

[juvenissun]

All the factors? What about cats and dogs and rats that have been at the game a lot longer and like a nice bit of fish waddling out of the water to meet them?

Yes, that is what I meant, all factors.

I think the world is still big enough to have some quiet places where it allows the fish to evolve into land animals.

See, here is the real consideration on how could evolution happen: Let's say the fish is a lung fish. Any single lung fish will not survive long enough to complete the evolution. But, the gene of the lung fish is evolving so in every generation (?), the lung fish can breath a little bit longer in air. Eventually, the lung fish will be more like an amphibian than a fish. So, a cat caught a lung fish may not be a problem at all in this process.

 

[juvenissun]

So... you adamantly reject evolution to the point of calling its subscribers "stupid", yet you think it is high likely that air-breathing fish like mudskippers and lungfish could evolve to become terrestrial animals?

Yes. This is the art of debate.

SunTze said: know your enemy, so you can win every time.

 

[Willtor]

I used the word fish, because I do not know the classification of fishes.

There are(?) some fishes today that they can breath in air. Do you think they have chance to evolve into land animals given a few more million years of time? I would think the chance is very high, consider all factors.

It could happen. I wouldn't hold my breath, though.

There would have to be an impetus to move further and further onto land in a gradual way. One can't reason that there is a "grand prize" at the end but lots of benefits along the way. Assyrian pointed out that there are predators that are very effective on land. This is a great hinderance. Maybe insurmountable.

 

[juvenissun]

It could happen. I wouldn't hold my breath, though.

There would have to be an impetus to move further and further onto land in a gradual way. One can't reason that there is a "grand prize" at the end but lots of benefits along the way. Assyrian pointed out that there are predators that are very effective on land. This is a great hinderance. Maybe insurmountable.

Let's take the lung fish as an example. The lung fish stays for a while in land environment (I am not sure what is the % of time) in its "normal" life activity. If the predators on land is a real threat, then the lung fish should not even exist at all. In other words, the lung fish has already survived its first step of "landing". So, even the predator is a threat, the evolution of lung fish should be able to continue onto its second step.

 

[gluadys]

Let's take the lung fish as an example. The lung fish stays for a while in land environment (I am not sure what is the % of time) in its "normal" life activity. If the predators on land is a real threat, then the lung fish should not even exist at all. In other words, the lung fish has already survived its first step of "landing". So, even the predator is a threat, the evolution of lung fish should be able to continue onto its second step.

Actually, the lung-fish does not really spend time "on land" at all. More like "in land".

Fooled by Nature: Lungfish : Video : Animal Planet

 

[juvenissun]

Actually, the lung-fish does not really spend time "on land" at all. More like "in land".

Fooled by Nature: Lungfish : Video : Animal Planet

Wonderful. Thanks. It makes me feel like snake is evolved from lungfish.