Researchers Trace Evolution To Relatively Simple Genetic Changes

[Mise]

Well, like I said, I don't know the details (a teacher explained it to me once in school, but all I can remember is that I agreed with her...). But again, "derogatory" means only in terms of "reproductivity", rather than what we would intuitively deem as "bad design". So I can only guess that land mammals, perhaps in parts of the world where flooding was frequent, developed the ability to exist for extended periods of time underwater, until such time that they had lost the ability to survive above water (e.g. the species that couldn't survive underwater died out and the species that could survive underwater stayed underwater [perhaps because there was more food there? less predators?] and eventually shed the redundant features from land survival). But like I said, I really don't know the details, and that's just a guess.

 

[carlosMM]

@Carlos:
Is any distinction made between two species who are biologically capable of mating but who "chose" not to for other reasons, and two species who are completely biologically incapable of mating?

well, there is no consensus on how to treat them

Personally, I prefer the following method, which is as far as I can judge becoming more and more common:


Species by massive morphological difference (that is, mating is phsyically impossible, elephant and mouse or crab and grass): morphological species
Species by sexual incompatibility that is nor externally obvious (horse and donkey): doesn't really happen in the wild for vertebrates, but common for wind-pollenatedplants. I call them incompatibility species
Species by behaviour (true for all morphospecies, usually, too): behavioural species.


Obviously, with fossils we can only distinguish morphospecies.

 

[carlosMM]

hasn't a horse and a zebra (or something like that) bred together recently? Or is this something else?

wolves and dogs breed in captivity.
and in the wild, there's perverts who do it, too - but it is a bit like you and a chimp breeding....

But normally, no wolf in his or her right mind will mate with such a funny creature that barks loudly, but cannot properly howl - and ignores ranking the in troop but for the alpha animal, actually also accepting a MALE as the SOLE alpha leader... UGH, what a perversion.....

Take the whales again: as far as we humans can tell, the only thing that keeps them from breeding is that they do not talk to each other! Makes them seperate species, strictly speaking.

Ok, if two people with brown hair have a kid, it will most likely have brown hair, but not always. Either way this is something alterable on humans, much like the plating on the fish. So yes, I do think things are changeable.

Well, hair color in humans is hardly selected for, so it is a bad example...

 

[carlosMM]

for whales (and other sea mammals) it is believed that they lived on land, then went to the water. I guess an alligator is a reptile though.

indeed, but better forget the term 'retile', use 'archosaur' and 'squamate' for alligators and snakes/lizards respectively. and so on

(reptiles is not a monophyletic group, and not even a monophletic group minus another monophyletic group (as dinosaurs is used in the sense of non-avian dinosaurs), but a horribly paraphletic group!)

I'm assuming there are two categories of change - one which is like hair color, a simple combination of genetics. The other being a abnormal mutation. This is the one I was saying it would take for a mammal to change it's arms to fins. These are usually derogatory changes, like being born with an extra finger, etc.

actually, no. But you are close to the truth...

there is only one category - change!
But some changes ALONE are insufficient to sperate two individuals reprodcutively. Others are sufficient.

now, as for the total restructuring of limbs: if you look at a whales paddle you'll notice that it is nothing but a 'deformed' hand. Proportions change, bones get omitted or fused, or in some other aquatic vertebrates they get duplicated. Basically, nothing new, if you regard a small enough step.

 

[carlosMM]

Well, like I said, I don't know the details (a teacher explained it to me once in school, but all I can remember is that I agreed with her...). But again, "derogatory" means only in terms of "reproductivity", rather than what we would intuitively deem as "bad design". So I can only guess that land mammals, perhaps in parts of the world where flooding was frequent, developed the ability to exist for extended periods of time underwater, until such time that they had lost the ability to survive above water (e.g. the species that couldn't survive underwater died out and the species that could survive underwater stayed underwater [perhaps because there was more food there? less predators?] and eventually shed the redundant features from land survival). But like I said, I really don't know the details, and that's just a guess.

pretty much right on target: what happened is that some predators were slightly better at catching prey on the shore by following it a bit deeper intot he water than others, and a bit deeper, and deeper... and especially by swimming (think otters today). Within this group, obviously, selection would favor the better swimmers. Sure they'd have trouble huting on dry land now, but there's so much prey in the water close to the shore that nobody else taps into so well!
So they multiplied, all thet ime getting selected for better swimming and diving performance, while previously selected-for abilitites (walking, running, sturdiness of the skeleton) were unimportant now. As far as they conflict with swimming they were even de-selected.

As a result you end up with animlas that are quite similar in the Grundplan (basic plan) to land vertebrates, but differ significantly in expression of this plan.

 

[MeteorPunch]

(reptiles is not a monophyletic group, and not even a monophletic group minus another monophyletic group (as dinosaurs is used in the sense of non-avian dinosaurs), but a horribly paraphletic group!)

I'm gonna have to download a few years worth of info to catch up on your terminology!

 

[The Last Conformist]

Considering how little DNA difference there is compared to how things look, you'd be suprised at how minor a change that is. (My guess would be at the most a 1% overall DNA change, much more likely a tenth of that) Humans are 11% yeast and 50% house fly after all. Largely changed appearances don't necessarily translate largely changed DNA codes.

I'm getting awfully tired of this DNA count fetishism ...

You only need knock out a control gene or two to create a human lacking a neocortex (the "thinking" and sense-processing part of the brain). To assert that the possession/lack of a neocortex is a minor thing is preposterous, as should be obvious to anyone that's got one.

While less critical than a mammal neocortex, removing the armour of that fish is gonna have fairly profound effects on it's biology, affecting vulnerability to attack, swimming speed, metabolic needs, and no doubt other things. What percentage of genes need be changed to achieve it has no impact whatsoever on the magnitude of that importance.

 

[The Last Conformist]

I'm gonna have to download a few years worth of info to catch up on your terminology!

This might be of help:
http://www.palaeos.com/Systematics/Cladistics/cladistics.htm

 

[carlosMM]

I'm gonna have to download a few years worth of info to catch up on your terminology!

just ask!


monophletic group: one species (or better, one or more properties) and all descendants.

thus dinosaurs must either INCLUDE birds or it is not monophletic.

paraphletic = not monophletic.

reptiles (as based on living ectotherm vertebrates: crocodils, alligators, montior lizards, lizards, snakes, turtles) is a very bad clade: a crocodile is far more closely related to a bird than to a turtle or lizard! They also differ so significantly in morphology and biochemistry that actually there is more similarity between any given mammal and certain extinct archosaurs (crocodiles, alligators, dinosaurs, pterosaurs, note that thre is a last common ancestor of crocs and birds and dinos that is NOT an ancestor of turtles or snakes!).


feel free to aks any Q, via PM or here!
Or make a new thread with your Qs and PM me the link!

I'll be away for three weeks but hope to have intermittent access.

 

[MeteorPunch]

Thanks for the link (TLC) and help (CarlosMM).

I can only express my views in simple terms at this point. In each of these threads, words/ideas come out that I am unfamiliar with. I'm basically just going on my common sense and lack any valid scientific knowledge.

I got a book, "evolution: the triumph of an idea" by Carl Zimmer, so I'm hoping it will teach the basics.

...then I'll be back to argue more fully!

 

[carlosMM]

Thanks for the link (TLC) and help (CarlosMM).

I can only express my views in simple terms at this point. In each of these threads, words/ideas come out that I am unfamiliar with. I'm basically just going on my common sense and lack any valid scientific knowledge.

I got a book, "evolution: the triumph of an idea" by Carl Zimmer, so I'm hoping it will teach the basics.

...then I'll be back to argue more fully!

I do not know how much basic science (biology and paleontology) you know. In case you need basic info:
as I posted elsewhere:
Neil A. Campbell Biology
a bit outdated, even the latest edition, but good for a general overview:
Mike Benton Paleontology

 

[Shaihulud]

Okay we know that a small genetic change can express a large difference phenotypically. Humans are the same species right? Genetically identical from one another, but our physical appearances are so much different from each other. Is there any good reason why? I don't think the time that humans took to settle over all the continent allows us to evolve such a difference. Same with all domesticated animals, i guess.

 

[The Last Conformist]

Okay we know that a small genetic change can express a large difference phenotypically. Humans are the same species right? Genetically identical from one another, but our physical appearances are so much different from each other. Is there any good reason why? I don't think the time that humans took to settle over all the continent allows us to evolve such a difference.

Why don't you think that?

Same with all domesticated animals, i guess.

That's not really comparable, since domest animals have been purposely bred to enhance or repress certain traits.

 

[Shaihulud]

Wellbecause we didn't have the time to settle down to evolve such a difference, we had what? 100,000yrs in a single region, not to speak of those pesky cross-breeding with those neighbours to stop diversification.Im surprised that people still look so different from each other, so I surmised that it might be a small change within the gene pool that stayed in the region that made the difference.

 

[The Last Conformist]

Skin colour correlates a bit too well with latitude to admit any explanation that doesn't include selection, but no doubt there's also been an element of founder effect.

 

[carlosMM]

Skin colour correlates a bit too well with latitude to admit any explanation that doesn't include selection, but no doubt there's also been an element of founder effect.

add to that that our technological advantages and the shift to brain power as the main selected attribute open a LOAD of doors, especially with regards to looks.

If, e.g., you can cover sensitive skin with clothes it doesn't matter what the skin looks like.
If, e.g., you can see well by shading your eyes with your hand or a hat and wiping away sweat with a cloth it doesn't matter what your eyebrows look like.
If, e.g., you can grtind your food, or cook it, and cut it, it doesn't matter what your jaw musculature and teeth look like. And these directly influence your profile, especially the cheekbones.

So in humans it is no surprise that mutation which would be unfavorable in 'normal' animals are beniging and thus preserved,

Ass to that a founder effect and you end up with lots and lots of local versions, now mix them up and recombine at will.... no surprise we look so diverse, while other aspcets are still so similar (only think of immunology!)

 

[CrazyScientist]

add to that that our technological advantages and the shift to brain power as the main selected attribute open a LOAD of doors, especially with regards to looks.

If, e.g., you can cover sensitive skin with clothes it doesn't matter what the skin looks like.
If, e.g., you can see well by shading your eyes with your hand or a hat and wiping away sweat with a cloth it doesn't matter what your eyebrows look like.
If, e.g., you can grtind your food, or cook it, and cut it, it doesn't matter what your jaw musculature and teeth look like. And these directly influence your profile, especially the cheekbones.

So in humans it is no surprise that mutation which would be unfavorable in 'normal' animals are beniging and thus preserved,

Ass to that a founder effect and you end up with lots and lots of local versions, now mix them up and recombine at will.... no surprise we look so diverse, while other aspcets are still so similar (only think of immunology!)

I agree with everything you say here, but I think the diversity in appearance among humans is also a matter of human perception. Both our biology and our psychological development predispose us to be able to distinguish small differences in the specific appearance of human faces. It seems possible to me that individuals of other species may be just as diverse in appearance if one knows what to look for. That is, to a dolphin (or other social animal for which recognition of individuals is important) all humans may look pretty much the same but individual dolphins may be trivial to distinguish between.

 

[Shaihulud]

In the future humans will decide our own evolutionary pathways. Understanding how it all works out is marvellous achievement by our scientists. I only hope that our descendant decides intelligence is a worthwhile trait and not to spit the human species.

 

[Shaihulud]

By human standards in how we divide animals, we are pretty different from each other, skin tones, hair, size, bone structure etc, not just facial differences. Dolphin might use a different standard of measure. I believe that utilizing Ultrasonic soundwaves is part of their senses? Then there might be subtlities involved that are beyond human understanding.

 

[carlosMM]

I agree with everything you say here, but I think the diversity in appearance among humans is also a matter of human perception. Both our biology and our psychological development predispose us to be able to distinguish small differences in the specific appearance of human faces. It seems possible to me that individuals of other species may be just as diverse in appearance if one knows what to look for.

It is true that once you know what to look for you'll notice more variety. And the opposite is true, too: initially, all Chinese looked the same to me.