Evolutionists: How did legs evolve?

[iouae]

This thread seems to have lost its legs.

 

[Silent Hunter]

This thread seems to have lost its legs.

Quite true and its because creationists make promises they know they can't deliver :sigh:.

 

[iouae]

I was watching TED and Elizabeth Blackburn happened to be speaking about cell ageing. She won a Nobel prize for discovering the enzyme telomerase which lengthens the ends of the chromosomes, protecting them from ageing. Absolutely fascinating, and relevant to human longevity too. We age because our telomeres shorten. But this does not have to happen. The enzyme telomerase maintains the telomeres.

Have y'all heard of this, or is just me in the dark?

https://www.nobelprize.org/nobel_prizes/medicine/laureates/2009/press.html

 

[Jonahdog]

I was watching TED and Elizabeth Blackburn happened to be speaking about cell ageing. She won a Nobel prize for discovering the enzyme telomerase which lengthens the ends of the chromosomes, protecting them from ageing. Absolutely fascinating, and relevant to human longevity too. We age because our telomeres shorten. But this does not have to happen. The enzyme telomerase maintains the telomeres.

Have y'all heard of this, or is just me in the dark?

https://www.nobelprize.org/nobel_prizes/medicine/laureates/2009/press.html

Be careful what you wish for. Cancer cells usually have lots of telomerase, that is why they can keep dividing.
Once again, science is a little more complicated than you wish it to be.

 

[iouae]

Be careful what you wish for. Cancer cells usually have lots of telomerase, that is why they can keep dividing.
Once again, science is a little more complicated than you wish it to be.

Yes, Elizabeth mentioned cancer in her talk, exactly as you said.

The trick to getting cells to divide forever, and hence to halt ageing is to maintain the telomeres while suppressing whatever it is which causes cancer. At least, in the last few years, we have made a big leap forward in understanding ageing.

She also mentioned how attitude of mind can maintain, or wear away the telomeres. This is the science of epigenetics I believe. Feeling in control, instead of a victim can prolong the telomeres, as can many good lifestyle choices no doubt.

 

[Shubee]

I'm hoping that there is an evolutionist here on TOL who would be willing to give a reasonably brief while still conceptually detailed explanation of how legs evolved.

What use are paralyzed legs or uncontrollable stubs? How did legs get their start? Many animals don’t have legs. But if prototype legs worked well enough to confer a small advantage for an animal to get closer to food or to escape a predator, then it doesn't matter how small and un-leglike the first legs were. However slight an improvement can be, it can make the difference between life and death. Natural selection will then favour slightly better, prototype legs. When these inefficient legs have become the norm, then a slight further increase in leg functionality will make the difference between life and death. And so on, until we have proper legs. See Richard Dawkins, The Blind Watchmaker, pp. 89-90.

 

[iouae]

What use are paralyzed legs or uncontrollable stubs? How did legs get their start? Many animals don’t have legs. But if prototype legs worked well enough to confer a small advantage for an animal to get closer to food or to escape a predator, then it doesn't matter how small and un-leglike the first legs were. However slight an improvement can be, it can make the difference between life and death. Natural selection will then favour slightly better, prototype legs. When these inefficient legs have become the norm, then a slight further increase in leg functionality will make the difference between life and death. And so on, until we have proper legs. See Richard Dawkins, The Blind Watchmaker, pp. 89-90.

I don't see too many critters around with prototype anything dragging behind them.
The opposite argument would be that having something useless hanging off one, till they develop some function, would confer a disadvantage, and contribute to extinction more than to advantage.

 

[Greg Jennings]

I'm hoping that there is an evolutionist here on TOL who would be willing to give a reasonably brief while still conceptually detailed explanation of how legs evolved.
That might sound like a weirdly specific request but I have a reason for asking it. It isn't a trick question. I really do want to focus on legs - any legs! Where did they come? What preceded them? What was the incremental genetic mutation that became legs? Note that legs almost always come in pairs and that there is all kind of various sizes, lengths, and configurations of legs. Did all these different types of legs show up separately or did they evolve from each other? Etc, etc, etc.
My question is not necessarily only about the first appearance of legs but also the current incarnations of legs in general. Where did legs come from and how did we get to the current state of legs. Why, for example, do dogs have four legs while ants have six and spiders eight. Why do some legs have three joints while other have more or less? Just whatever you can think of about legs and how does the theory of evolution explain what we see?

And I don't intend to try to pick apart whatever explanation is offered. It isn't about that. I'm simply curious to know what evolution has to say about legs and why they exist and how they got here. Feel free to just offer whatever it is you understand to be what evolutionary theory has to say on the topic.


Thanks,
Clete

Did you get an adequate answer?

If not, I'd be happy to explain

 

[Clete]

Did you get an adequate answer?

Nope

If not, I'd be happy to explain

By all means.

 

[The Barbarian]

Clete, I think I'll just watch this one, this time. If I think I can help, I will, but I'm not hopeful this will end any better than it did the last time.

 

[Greg Jennings]

Nope


By all means.

Ok!

1. Lobe-finned fish are the first to ever exist with bones. Prior to them, it was just sharks, skates, rays, and fish that either have no rigid internal structure (think hagfish) or those with osteoderms (natural plate armor) on the outer surface

2. Lobe-finned fish are called so due to their stubby, almost leg-like appendages. Their fins have become more rigid and compact. Look up a coelacanth to see a good example. Some lobe-finned fish (henceforth called lobies) alive today use their stubs to "walk" along the bottom of the ocean. That is exactly what happened to shallow water lobies: some started to crawl.

3. After millions of years of evolution, we have a lobie that has adapted to breathe air briefly, a fantastic way to avoid predators in a world where all of those predators are underwater. Likely this occurred via the swim ladder being co-opted into a simple lung (something that lungfish today, as well as arapaima, and some catfish, can still do now: breathe air with their swim bladder or lungs). The stubby fins become more and more leg-like as the eons pass, because the lobies that CAN get out of the water don't get eaten as often as those that cannot, and they survive and reproduce.

4. A few million more years and we have a creature that needs water to survive, but can also come out of it if necessary and for long periods of time. There is no competition on the land for food because nobody else is here yet, other than Arthropods. This creature flourishes with its stubby legs that it uses to drag its body along (like a mudskipper).

5. Those stubs are refined over millions of years until they are primitive legs, like those that a newt would have. And in fact, this is where the fish become amphibians. The legs get refined over time due to this: those creatures with a better ability to move around on land are better adapted to survive and reproduce. You start with a knub, and in the next few thousand years a mutation produces lengthened fin bones, which over many more millions of years become digits (think: whale fin bones for a crude example). And voila, you have a working leg.

Hope that was helpful.

 

[Greg Jennings]

I don't see too many critters around with prototype anything dragging behind them.
The opposite argument would be that having something useless hanging off one, till they develop some function, would confer a disadvantage, and contribute to extinction more than to advantage.

Then you aren't looking hard enough.


Mudskippers, lungfish, and many catfish species actually use their fins to walk on land. And in the case of the lungfish, it has a primitive lung too.

There are lizards without legs, and all large constrictor snake species have "claspers" where hind legs used to be. They have one digit with a claw and are primarily used in mating now.

Wings were not around for much of the time that feathers existed. Feathers began as small filaments that covered the body probably for warmth and possibly display for females. And they were on dinosaurs. Small tree-dwelling carnivorous dinosaurs were probably the first to develop broad feathers, as they would help them glide from tree to tree just like a flying squirrel would. And then eventually the still-fingered arms develop feathers that are long, broad, and tough. These are flight feathers, and even still the first "flyers" likely surfed the air waves more than true flying. But it's a small step from that to full-on flight

My point being, in order to be preserved within a population, these weird appendages/mutations must do something good for the organism. They must make its life easier than its non-mutant compatriots in some measurable way within a specific environment (or at the very least not hinder the animal). Otherwise, they will be eliminated via natural selection

 

[iouae]

Then you aren't looking hard enough.


Mudskippers, lungfish, and many catfish species actually use their fins to walk on land. And in the case of the lungfish, it has a primitive lung too.

There are lizards without legs, and all large constrictor snake species have "claspers" where hind legs used to be. They have one digit with a claw and are primarily used in mating now.

Wings were not around for much of the time that feathers existed. Feathers began as small filaments that covered the body probably for warmth and possibly display for females. And they were on dinosaurs. Small tree-dwelling carnivorous dinosaurs were probably the first to develop broad feathers, as they would help them glide from tree to tree just like a flying squirrel would. And then eventually the still-fingered arms develop feathers that are long, broad, and tough. These are flight feathers, and even still the first "flyers" likely surfed the air waves more than true flying. But it's a small step from that to full-on flight

My point being, in order to be preserved within a population, these weird appendages/mutations must do something good for the organism. They must make its life easier than its non-mutant compatriots in some measurable way within a specific environment (or at the very least not hinder the animal). Otherwise, they will be eliminated via natural selection

Greg, you have done the work for me by explaining how all these things like "claspers" have functions.

If you were to look at animals around today, show me organs which have no uses?
The appendix or tonsils which they used to whip out, do have functions in the immune system, and the appendix stores bacteria. Where do we find today animals with organs that are no use?

Let's take an example - say an albino crocodile. That has selective advantage against it for sunburn reasons, and easy to spot reasons. And two headed snakes barely survive, not to mention survive long enough to breed more two headed snakes. And two heads is better than one

So find me organisms with vestigial and useless whatevers around today.

Take an example. First there were wingless insects.

Then "hey presto" there were flying insects. I don't think they have found between insects in the fossil record, or insects having wings which did not fly.

And even our flightless birds today, penguins use their wings to swim, and ostriches use their wings to run, and to act big in fighting, to frighten things away, and to keep themselves warm etc. And why should God not make flightless birds with wings, seeing as they all seem quite happily surviving today.

Take a peacock with what looks like a super-useless tail, only used for impressing its mate and us. It seems useless and a pain, but God gives creatures things they have to carry around, partially because He can, and because He loves variety.

I don't mean to be crude, but thank God for human female breasts. All other mammals only have nipples.

 

[Greg Jennings]

Greg, you have done the work for me by explaining how all these things like "claspers" have functions.

If you were to look at animals around today, show me organs which have no uses?
The appendix or tonsils which they used to whip out, do have functions in the immune system, and the appendix stores bacteria. Where do we find today animals with organs that are no use?

Let's take an example - say an albino crocodile. That has selective advantage against it for sunburn reasons, and easy to spot reasons. And two headed snakes barely survive, not to mention survive long enough to breed more two headed snakes. And two heads is better than one

So find me organisms with vestigial and useless whatevers around today.

I like you. You can think. Respect.

In humans, I think the best example of a truly vestigial feature would be goosebumps. For mammals, goosebumps are little skin pockets that can fill with air to help fluff the fur, making the animal appear bigger and possibly warming it as well. In humans, we simply don't have enough hair to make that happen. In fact, you could argue that human body hair itself is vestigial, as it serves no purpose other than on top of our heads where it keeps heat in.
We also have the remnants of a nictitating membrane (the foggy lens that reptiles and birds can use to shield their eyes in water. You can see it in the outside corner of your eyeballs. It serves no real purpose now.

In whales, I'm sure you've heard of the fingers inside a whale fin, a vestige from their terrestrial ancestors like Andrewsarchus (which is interestingly a wolf-like hoofed predator related most closely to sheep). They also have small hindleg remnants at the pelvic line.

This isn't vestigial I know, but a support for bird-dinosaur evolution has come from genetics labs working on chicken embryos. By turning certain genes on or off, the produced chickens with teeth and a long bony tail.


I would argue against most flightless birds having vestigial wings. Large ones like emus and ostriches use them for balance in running and mating, and seabirds use them to swim efficiently. However, something like the Dodo bird had no real function for its little wings. Unfortunately they've been gone for a long time thanks to humans doing what we do best

 

[iouae]

I like you. You can think. Respect.

In humans, I think the best example of a truly vestigial feature would be goosebumps. For mammals, goosebumps are little skin pockets that can fill with air to help fluff the fur, making the animal appear bigger and possibly warming it as well. In humans, we simply don't have enough hair to make that happen. In fact, you could argue that human body hair itself is vestigial, as it serves no purpose other than on top of our heads where it keeps heat in.
We also have the remnants of a nictitating membrane (the foggy lens that reptiles and birds can use to shield their eyes in water. You can see it in the outside corner of your eyeballs. It serves no real purpose now.

In whales, I'm sure you've heard of the fingers inside a whale fin, a vestige from their terrestrial ancestors like Andrewsarchus (which is interestingly a wolf-like hoofed predator related most closely to sheep). They also have small hindleg remnants at the pelvic line.

This isn't vestigial I know, but a support for bird-dinosaur evolution has come from genetics labs working on chicken embryos. By turning certain genes on or off, the produced chickens with teeth and a long bony tail.

Again, thank you for saving me much thinking, by the reference to genes which switch on and off.

If I were God, I would not reinvent the wheel every time I engineered a new animal. I would take existing code, and tweak it, to create the change I wanted.

And if in the process it leaves a nictitating membrane in the eye which seemingly has no use, but does not bother anyone, then so be it.

It is like a programmer who writes code. When I write code, I leave useless code in which I might use later. Or it just may be leftover, and doing no harm, so why try to remove it to make perfect code, when in the process I might upset another bit of code dependent on the code I am removing.

I am sure there is tons of dormant code in all computer programs for historical, or future use reasons which only the Programmer can account for. And whereas we may settle for "good enough" thank goodness God has high standards where "good enough" is pretty amazing. But I am one of the few around here who would actually say that sometimes God DOES just settle for "good enough" and not perfect.

That may leave an organism with a seemingly useless looking thingamajig - but it survives fine anyhow, and we still may find that thingamajig very interesting, adding to the diversity of life. I mean life does the most bizarre things - luckily we are too ignorant to hear of it till David Attenborough comes on TV to "wow" us.

 

[6days]

If I were God, I would not reinvent the wheel every time I engineered a new animal. I would take existing code, and tweak it, to create the change I wanted

You believe in an weak god who can't get things right. The Bible tells us about a Creator who is perfect and created all the land animals in one day. Nothing about tweaking in God's Word.

 

[Greg Jennings]

Again, thank you for saving me much thinking, by the reference to genes which switch on and off.

If I were God, I would not reinvent the wheel every time I engineered a new animal. I would take existing code, and tweak it, to create the change I wanted.

And if in the process it leaves a nictitating membrane in the eye which seemingly has no use, but does not bother anyone, then so be it.

It is like a programmer who writes code. When I write code, I leave useless code in which I might use later. Or it just may be leftover, and doing no harm, so why try to remove it to make perfect code, when in the process I might upset another bit of code dependent on the code I am removing.

I am sure there is tons of dormant code in all computer programs for historical, or future use reasons which only the Programmer can account for. And whereas we may settle for "good enough" thank goodness God has high standards where "good enough" is pretty amazing. But I am one of the few around here who would actually say that sometimes God DOES just settle for "good enough" and not perfect.

Very cool! I like the philosophy of this stuff.

My personal thoughts on evolution and God are thus (assuming God's existence of course):
God is certainly the most intelligent being of all time
God can tire, as we learn from the Genesis account.

Static creation is not an intelligent design. Making creatures that are screwed whenever the habitat changes a little bit, then having to create a bunch of new ones to replace them every time an extinction event occurs is just silly. I forget the exact number, but there have been a minimum of 4 mass extinctions through history (from the fossil record). If creation is really that taxing, and knowing there have been several events that nearly wiped out life here in the past, making static creatures that are doomed when change occurs is inefficient and arguably cruel.

It makes sense to me that the most intelligent being would use a highly efficient, off-hands approach to all creations. God gives creatures the ability to mutate and adapt to their environments. That way, even if 99.9999% of all life is wiped out, Earth will repopulate itself in time. Creatures will evolve and grow to fill the ecological niches opened up after an extinction. In fact, without the Cretaceous extinction that ended the dinosaurs reign, mammals would not have been able to grow and diversify, and humanity would lithely ever exist.
Perhaps, instead of creating again every time His creation is obliterated by a cosmic accident, God has engineered life to be (as a whole) basically indestructible. Evolution can make any Earth environment habitable.

Because that's what a loving creator would do. He would not sentence his creations to hopelessly die without a chance. He would give his cherished creation of life a chance.

Static creation with extinction events is simply not smart. Now, your add-on that God is basically driving the mutations changes that. But I prefer a more hands-off approach personally.
By making creatures with the ability to change and adapt to whatever is thrown at them, life is guaranteed to last

 

[6days]

In humans, I think the best example of a truly vestigial feature would be goosebumps

Your BEST example fails, just as claims about Junk DNA has failed (Likewise claims about pseudogenes, useless appendix, etc).
Your Best example is based on a false belief system. Goose bumps in humans do serve purpose, and your belief that they are evolutionary remnants, is simply a belief... not science.

 

[Greg Jennings]

Your BEST example fails, just as claims about Junk DNA has failed (Likewise claims about pseudogenes, useless appendix, etc).
Your Best example is based on a false belief system. Goose bumps in humans do serve purpose, and your belief that they are evolutionary remnants, is simply a belief... not science.

Goosebumps serve a purpose you say.....and that purpose is?

 

[iouae]

Very cool! I like the philosophy of this stuff.

My personal thoughts on evolution and God are thus (assuming God's existence of course):
God is certainly the most intelligent being of all time
God can tire, as we learn from the Genesis account.

Static creation is not an intelligent design. Making creatures that are screwed whenever the habitat changes a little bit, then having to create a bunch of new ones to replace them every time an extinction event occurs is just silly. I forget the exact number, but there have been a minimum of 4 mass extinctions through history (from the fossil record). If creation is really that taxing, and knowing there have been several events that nearly wiped out life here in the past, making static creatures that are doomed when change occurs is inefficient and arguably cruel.

It makes sense to me that the most intelligent being would use a highly efficient, off-hands approach to all creations. God gives creatures the ability to mutate and adapt to their environments. That way, even if 99.9999% of all life is wiped out, Earth will repopulate itself in time. Creatures will evolve and grow to fill the ecological niches opened up after an extinction. In fact, without the Cretaceous extinction that ended the dinosaurs reign, mammals would not have been able to grow and diversify, and humanity would lithely ever exist.
Perhaps, instead of creating again every time His creation is obliterated by a cosmic accident, God has engineered life to be (as a whole) basically indestructible. Evolution can make any Earth environment habitable.

Because that's what a loving creator would do. He would not sentence his creations to hopelessly die without a chance. He would give his cherished creation of life a chance.

Static creation with extinction events is simply not smart. Now, your add-on that God is basically driving the mutations changes that. But I prefer a more hands-off approach personally.
By making creatures with the ability to change and adapt to whatever is thrown at them, life is guaranteed to last

I agree with most of what you say, with this exception...

There have been many dozens of mass extinctions - it just depends on how you define one.

And I see God recreating, using old DNA, after each extinction event.

During the Triassic, Jurassic, Cretaceous era, God was on a Dinosaur/reptile "size-does-matter" phase.

Immediately after this, God goes back to what He started before the Triassic, He essentially goes back to animals shaped after the therapsid, mammal-like-reptiles of the Permian. After reptiles being so dominant, now mammals rule.

I see the whole Triassic, Jurassic, Cretaceous as God taking a side-trip.
Then He got back to the main business of making man in His image.
So all the animals become smaller, more mammal like, tame by comparison - and now we live in the Holocene - the time with the best climate and the most docile creatures - all perfect for puny man.