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TheBlackCat
2005-Oct-25, 02:52 AM
This was brought up in my biomedical engineering seminar series, and I thought it might be of interest to you all.


A single mutation may have caused gross anatomical changes that spurred human evolution


A pile of evidence from disparate disciplines indicates that a single change in a single gene - MYH16 - may be responsible for significant morphologic differences between humans and other primates, including possibly the increase in brain size that set the earliest species of Homo apart from their kin. This is the first protein disparity between humans and chimps that can be correlated to drastic anatomical changes seen in the fossil record, according to a group of University of Pennsylvania researchers who published a letter in the March 25 issue of Nature.

Full article: Bite makes way for brain (http://genomebiology.com/researchnews/default.asp?arx_id=gb-spotlight-20040326-01)


The basic idea is that a single frame shift mutation (where several nucleotides in a sequence were deleted) rendered an important protein for jaw muscle development inoperable at the border between hominids and austrolopithecines. The same section of the gene is found in all the primates that were studied except for one, humans, and all humans studied (including people from 6 seperate geographic groups) carried the exact same mutation. The result of the mutation is a significant decrease in the size and strength of jaw muscles in those affected by the mutation. The hypothesis is that this reduction in the jaw muscles reduced restrictions on brain case size that were imposed by the jaw muscles. This made it possible for far large brain cases, and thus brains, to evolve rapidly.

The idea is still somewhat controversial, but if it is true the implications are enormous. The idea that such a simple change, and in fact what most would assume would be a harmful effect (the complete inactiviation of a key protein due to a mutation) could have actually been the one of the ultimate causes that spurred human evolution is very significant (although not altogether surprising).


For some, however, the findings may be hard to swallow. "Even if it's a scientifically based just-so story, it's still a little bit of a just-so story... We can't really prove it, but I think there are enough morphological characters that changed in concert that could all be explained by this mutation that there really is a parsimony to it that is quite striking and makes it quite believable," Tabin said.

Enzp
2005-Oct-25, 05:17 AM
I have a hard time with it. Just because the jaw got smaller doesn't mean the brain instantly fills in the space. SO what would be the survival advantage of the smaller jaw? In other words, why would this survive preferentially over the existing forms long enough to grow a new larger brain? This really sounds like after the fact rationalizing. (I suppose that is somewhat redundant.)

The Neanderthals had larger jaw muscles AND larger brains than we do. And other than the occasional TV commercial gig, what good did it do them? Well, besides the better car insurance rates?

Frankly I would think it went the other way. Increased mental capacity allowed greater variety in diet thus reducing the need for powerful jaws to crush seeds and plant fibers. Assuming the two are even linked at all.

Correlation is not causality.

SirBlack
2005-Oct-25, 07:50 AM
I have a hard time with it. Just because the jaw got smaller doesn't mean the brain instantly fills in the space.

From the sound of it, this mutation didn't directly change the brain/skull size. But it lifted the constraints on further mutations doing so.

From the article:

Loss of such muscle mass would affect survival, and also development, as the forces muscles exert have been largely implicated in sculpting bone structure. Stedman cited, as an example, studies involving specific knockout mice, which have doubled muscle mass (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9139826&dopt=Abstract%20%20%20) accompanied by altered bone structure (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10962344&dopt=Abstract%20%20%20). "This is built-in precedent for a causal relationship," Stedman said. Kaplan offered the effects on children afflicted with polio as an example. "They have normal genes, but they have abnormal muscle pull because the nerves to the muscles aren't working," he told us. "By deactivating the muscle, you can see dramatic effects on the skeleton."

So it seems if a strong-jawed hominid had a brain-increasing mutation, the expansion of the skull would be limited during development by the jaw muscle. Whereas in a weak-jawed hominid, the same brain mutation could have a much larger effect.

Perhaps such brain-increasing mutations could have already been in the population but had to wait until this jaw-reduction mutation came along?


The Neanderthals had larger jaw muscles AND larger brains than we do.

Hmmm. Is Neanderthal jaw muscle size (in whatever measure is appropriate here) much closer to humans or other primates?

TheBlackCat
2005-Oct-25, 04:15 PM
Another issue is that the brain size could have increased some. This could have altered diet and behavior in such a way that it rendered the increased jaw muscles obselete. Although the brain was larger than other primates, these large jaw muscles created on upper limit on the brain case size that could not be overcome. Any evolutionary attempts to do so were ineffective, either because the traits could simply not be expressed or because the conflict between brain size and the jaw muscles was detrimental. When the now obselete jaw muscles were done away with, the limit on brain size was lifted and the brain could further increase. This is just one possible scenario. Sir Black's is equally plausible.

Like all hominids, Nenderthals have much smaller jaw muscles than other primates. They may have been larger than those of humans, but not as large as those of apes.

JHotz
2005-Oct-25, 10:31 PM
I have a hard time with it. Just because the jaw got smaller doesn't mean the brain instantly fills in the space. SO what would be the survival advantage of the smaller jaw? In other words, why would this survive preferentially over the existing forms long enough to grow a new larger brain? This really sounds like after the fact rationalizing. (I suppose that is somewhat redundant.)
Perhaps a smaller jaw allows clearer verbal articulation. Just a guess.

aurora
2005-Oct-25, 11:14 PM
human brains have tended to get larger, but we have constraints on our head size at birth, even though humans are born helpless.

Just a thought.

Gillianren
2005-Oct-26, 08:50 PM
human brains have tended to get larger, but we have constraints on our head size at birth, even though humans are born helpless.

Just a thought.

Well, sure. That's because, were the human head any larger at birth, it would kill most of the babies and mothers. (My daughter's head didn't change shape when she was born. Yeow!) This is one of my primary examples of "design flaw" to point out to IDers. Human babies must finish brain development outside the womb because biology prevents them from finishing it inside.

aurora
2005-Oct-27, 02:50 PM
Well, sure. That's because, were the human head any larger at birth, it would kill most of the babies and mothers. (My daughter's head didn't change shape when she was born. Yeow!) This is one of my primary examples of "design flaw" to point out to IDers. Human babies must finish brain development outside the womb because biology prevents them from finishing it inside.

Yes, so I was thinking that if, say, the jaw got smaller it would increase the space available for brains, since there is an upper limit on the total size of the head.

As someone else pointed out, that doesn't mean that brains would automatically expand to take up all the available space, but if there was evolutionary pressure for larger brains then given enough time it would happen.

wayneee
2005-Nov-22, 03:16 AM
Yes, so I was thinking that if, say, the jaw got smaller it would increase the space available for brains, since there is an upper limit on the total size of the head.

As someone else pointed out, that doesn't mean that brains would automatically expand to take up all the available space, but if there was evolutionary pressure for larger brains then given enough time it would happen.

I was thinking about what the mutation would signify in the survival of the recieved. Strong jaw muscles in the hominids where primarly for eating, and prehaps for mating, and less so for protection. Predators of the hominids would have no trouble over coming strong or weak jawed primates. The Strong Jaw characteristic might have been a sexual preference, and the Strong Jaw might have been useful in innner pod fighting. Moreso the diet of the Stronger jawed hominids must have been tough to chew. Prehaps Biting through bones or bivalves for calcium. The Weak Jawed would be at a disadvantage, therefore the need to problem solve .

I have always had issue with the Brian size body ratio thearum, as we do know its not the size but the surface area of the brain that accounts for complex reasoning.

I believe adversity is a crap shoot in Natural Selection. It either kills the mutant outright , or leads the mutated to fill in some ecological gap. The Weak Jawed would have to have done things differently , instead of biting through Clam shells, they might observe certain birds hitting against rocks. Prehaps it lead the way to food expiermentation, to see what was edible, some that was plentiful and not utilized by the strong jawed.

TheBlackCat
2005-Nov-22, 03:21 AM
I was thinking about what the mutation would signify in the survival of the recieved. Strong jaw muscles in the hominids where primarly for eating, and prehaps for mating, and less so for protection. Predators of the hominids would have no trouble over coming strong or weak jawed primates. The Strong Jaw characteristic might have been a sexual preference, and the Strong Jaw might have been useful in innner pod fighting. Moreso the diet of the Stronger jawed hominids must have been tough to chew. Prehaps Biting through bones or bivalves for calcium. The Weak Jawed would be at a disadvantage, therefore the need to problem solve .
Tough jaws help eating tough food. Cooking can soften food and make it easier to eat.


I have always had issue with the Brian size body ratio thearum, as we do know its not the size but the surface area of the brain that accounts for complex reasoning.
You can only squeeze so much surface area into a given volume. There still must be enough room for all the white matter that makes connectsion between various parts of the neocortex and between the neocortex and the rest of the brain.


I believe adversity is a crap shoot in Natural Selection. It either kills the mutant outright , or leads the mutated to fill in some ecological gap. The Weak Jawed would have to have done things differently , instead of biting through Clam shells, they might observe certain birds hitting against rocks. Prehaps it lead the way to food expiermentation, to see what was edible, some that was plentiful and not utilized by the strong jawed.
There are no clams in the Great Rift Valley.

Ken G
2005-Nov-22, 04:21 AM
My question is, which of these scenarios is closer to the truth:
1) all protein differences have been examined to explain the difference in human intelligence, and the only one that seems to have any connection is the one responsible for jaw muscle size, or
2) of many many possible differences, the one that presently has the most clearly demonstrable connection with a mutation that might conceivably affect intelligence is responsible for jaw muscle size.

When all you have is a hammer, everything looks like a nail.
Still, this scenario raises an interesting issue, that I always wondered about. Surely, the first animals with this new mutation would have been considered horribly disfigured by the rest. How would that have affected his/her mating chances? Did it have to be a female, for example (assuming early humanity followed the model of female as "gatekeeper")? And what disfiguring mutation of modern humanity is going to usher in the next superior modification?

wayneee
2005-Nov-22, 04:30 AM
You can only squeeze so much surface area into a given volume. There still must be enough room for all the white matter that makes connectsion between various parts of the neocortex and between the neocortex and the rest of the brain.
The human brain get around the whole mass of brain thingy by being convoluted and recessed, we see in other species that we can rate intelligence via amount of convolution in the surface Grey. Blue Whales for example have enormous Brains 6 Kg as humans have almost 2kg The proportion to body wieght issue would show that the blue whales brain is about .01 percent of its entire wieght as a human is almost 2 again. Heres the quandry with that theory, a rats ratio is 1.5, a chimps nearly identical to a human.
Where the vast difference arrisses is on the disection table, as we view the convolutions in the brain. How this relates to little jaws i can only sepeculate,not enough brain research to speculate on the evolution of recesses and convolutions. The Brain does not fossilize well. It would be interesting if we could determine if the convolutions in grey matter change in depth throughout life, as the brain use is needed for higher purpose.
I have read Science Fiction where intellect was derived by a certain species because of a worm infection in its brain created more surface area as the worms burrowed through eating whatever they were eating

TheBlackCat
2005-Nov-22, 05:26 AM
Yes, the surface area is important. My point is that there is an upper limit as to how much folding you can have in the grey matter and still have a functional brain. Having a bunch of grey matter folded titly into the brain is useless if the cell bodies of the neurons (which is what differentiates grey matter from what matter) do not connect to anything. The basic functional unit of the neocortex is the column. It is a small region of neocortex grey matter stretching from the surface of the brain to the white matter below. It is a gross oversimplification because different parts of the cortex serve different purposes, but basically the more columns an organism has the smarter it is. The surface area of the cortex is basically proportional to the number of columns in the cortex. Increase the surface area, increase the number of columns, increase intelligence (that is the grossly oversimplified version). So why isn't the brain just packed solid with columns? Because columns alone don't do anything. The purpose of columns is to recieve information, process it, then send it elsewhere. There must be connections to, from, and between columns for them to be of any use. Think about a CPU. If you have a loose CPU sitting in a shoebox somewhere it will not do anything, it must get information to process and send that information elsewhere for it to be of any use. That is the purpose of the white matter which, at least in the neocortex, is underneath the grey matter. The white matter mostly contains neuron axons that connect various columns to each other and to other parts of the brain. If you make the folds too deep, to closely packed, or with too many layers of folds then there will not be enough room for the axons to make connections, and the extra processing power will not do anything. There must be enough room left over for these axons to make their connections. This means there is a fundamental limit as to how much folding you can have and still have a functional brain. What is more, the columns are not infinitely thin. They have a finite depth. Geometrically, you can only fold an object with a finite depth to a certain tightness.

Now, as I was saying this is a gross oversimplification. Not all areas of the cortex are directly related to intelligence. There is no one "conciousness" region of the cortex, no one seat of what we call "intelligence", but there are areas that do not directly increase our intelligence, and there are columns that do not directly increase our intelligence. Increasing the number of columns in these areas will not aid intelligence at all no matter how many you add.

And the thing about worms eating holes in the brain is very wrong. It is not literally the surface area that is important, it is the number of columns. In an intact brain the number of columns is roughly a function of surface area. If you have worms eating through the brain, then it will increas the surface area but will decrease the number of columns because the columns will be eaten as well. The worms will also eat the axons in the white matter. This will sever the connections to other columns in other parts of the neocortex. Without their connections, these neurons will also die (in the brain, "use it or lose it" is the rule for neuronal activity, neurons that are not working die). So far from increasing intelligence, this will cause a significant decrease in intelligence as well as the failure of various parts of the brain. For instace they will likely lose the ability to control certain parts of their body, or see certain parts of the visual scene, or process certain types of motion of detect certain types of objects in the visual scene. In the end, such worms would probably leave the host pretty incapacitated.

And before you ask: no you cannot make the columns smaller or thinner, they are limited by the number of cell bodies they must have in them to do the required processing; no you cannot make the cell bodies smaller, they are the size they are because that is the size they need to be to do their job; and no you cannot scatter columns throughout the cortex, it might theoretically be possible but that is not how mammal (maybe even all vertebrate) brains are organized, it is highly conserved between species so either it is necessary from a functional standpoint or changint the development of the neocortex is unfeasible from an evolutionary standpoint.

And you can get an idea of the degree of folding from fossils. The brain may not fossilize well, but the brain leaves impressions on the inside of the skull. The impressions left by the sulci (plural of sulcus), as the folds are called, can be seen on the inside of the skull if it is well enough preserved.

01101001
2005-Nov-22, 05:57 AM
There are no clams in the Great Rift Valley.

Where did they go?

Diagram: Endemic species of molluscs from Lake Tanganyika (http://www.d.umn.edu/llo/Ideal/figure8.html)

That Grandidiera burtoni sure looks like a clam.

Edit: Even better: Sibiloi National Park Online Exhibit :: Lake Turkana (http://www.sibiloi.com/ancient.htm)


Many different mollusk species in habited the lake and rivers, gastropods, clams and fresh water oysters.

Enzp
2005-Nov-22, 06:24 AM
Do not assume that there was all of a sudden POOF small jawed/ large brain caivty beings. The change developed slowly over a long time. It evolved. That is without assigning causailty to any thing, no chicken vs egg thing. Whatever caused what, it did it over eons, not all of a sudden. So there was no grotesque fellow with a tiny jaw showed up in downtown village one day.

Ken, I think you missed the OP. It didn't sate, I don't believe, that whatever proteins caused a jaw difference also caused a brain difference. The OP was that as the jaw shrank, it left more room for the brain to develope larger. That is not a direct conection.

My personal view is that they are not mutually exclusive as I mentioned in that the Neanderthals had larger jaws AND larger brains than we do.

Furthermore, part of this scenario is assuming that brain size and intelligence are directly linked and proportional. I make no such assumption in my own thoughts. Your two choices assume certain things that are not in evidence. brain size and jaw size seem to have a reverse correlation. There is no evidence as to causality in that.

Ken G
2005-Nov-22, 06:44 AM
Whatever caused what, it did it over eons, not all of a sudden. So there was no grotesque fellow with a tiny jaw showed up in downtown village one day.

I had the sense from the OP that it was a single mutation, that messed up the proteins that develop the jaw muscle. So I would have thought that indeed there would be a rather grotesque fellow, though I speculated it might have had to be a grotesque female, hopefully without sounding sexist (in fact I know little of the mating habits of pre-humans. It's hard enough to figure out the habits of current humans...). Of course that individual wasn't smarter, that part would have taken a long time. But I agree with Enzp's initial suggestion, it seems hard to understand how the weak jaw could have just hung around long enough for intelligence to appear. It would make more sense as a beneficial mutation after a strong jaw was no longer needed, due to feeding changes connected with higher intelligence. But I defer to the bioengineers!

wayneee
2005-Nov-23, 04:32 AM
Now, as I was saying this is a gross oversimplification. Not all areas of the cortex are directly related to intelligence. There is no one "conciousness" region of the cortex, no one seat of what we call "intelligence", but there are areas that do not directly increase our intelligence, and there are columns that do not directly increase our intelligence. Increasing the number of columns in these areas will not aid intelligence at all no matter how many you add.


Your knowledge of the brain seems to be extensive,I try and not step into this gooey subject lightly. I was aware of most of the things you stated. The Columns you spoke of are new to me though , prehaps I understand this concept differently. I wouldnt mind clarification on this ,or even a link if your tired of typing
Well where I was going with this whole brain size issue was going to relate back to the issue. The mutation is there, its been done , and apparently was part of our evolutionary chain. Mutations happen all the time, mostly benign and useless. Here a mutation which seems to give a definate handicap seems to have lead to some boon. I can only think of diet. As if nutrition needed to be discovered from a different source in some oppurtune time during the emergence of the mutation. Its the why is the mutation significant, and I dont see relaxed jaw structure allowing brain cavity expansion as being the result.

wayneee
2005-Nov-23, 04:44 AM
I had the sense from the OP that it was a single mutation, that messed up the proteins that develop the jaw muscle. So I would have thought that indeed there would be a rather grotesque fellow, though I speculated it might have had to be a grotesque female, hopefully without sounding sexist (in fact I know little of the mating habits of pre-humans. It's hard enough to figure out the habits of current humans...). Of course that individual wasn't smarter, that part would have taken a long time. But I agree with Enzp's initial suggestion, it seems hard to understand how the weak jaw could have just hung around long enough for intelligence to appear. It would make more sense as a beneficial mutation after a strong jaw was no longer needed, due to feeding changes connected with higher intelligence. But I defer to the bioengineers!
I would agree Ken , some mutations are adrupt, although I dont think this chap would have been considered grotesque. More like the sexual difference between a Strong Jawed Jock and a Weak Jawed nerd. This mutated Male or female would not nessarily be driven away. These are hominids and we do know them to be social. A Male might find it hard to fend off Strong jawed Males and win mating privlages. But we have learned from studying Greater apes and Chimps, that passive males sneak thier DNA into the mix. If it was a female, the odds of her breeding are enorrmous , as studing chimps again , Females are rarely ever banished from the community. This mutation would have thrived if it didnt kill them with its deminishing ability to crunch down on what ever they were cruncing on.

Enzp
2005-Nov-23, 05:18 AM
I think we are still missing it. They didn't give birth to a new baby with...gasp...a weak chin line. These changes evolved over many generations. Willie Shoemaker did not of a sudden begat a line of Shaqs. Tiny incremental changes.

If you find a penny, you don't write your friends about it. A nickel is five times larger, yet you still don't find it significant. But if you find a penny every day and save it, after ten years you have enough to buy a couple Celine Dion CDs and a bottle of aspirin. Point being that over time change accumulates. (pun intended)

wayneee
2005-Nov-23, 05:31 AM
I think we are still missing it. They didn't give birth to a new baby with...gasp...a weak chin line. These changes evolved over many generations. Willie Shoemaker did not of a sudden begat a line of Shaqs. Tiny incremental changes.

If you find a penny, you don't write your friends about it. A nickel is five times larger, yet you still don't find it significant. But if you find a penny every day and save it, after ten years you have enough to buy a couple Celine Dion CDs and a bottle of aspirin. Point being that over time change accumulates. (pun intended)
Good joke, but bought gum istead of asprin , now Im looking for pennies again.
I understand what your saying but ,mutations which are carried sexualy, like family simularities, sickle cell, are definaely in the category of immediate. evolutionarily speaking. The long term developements that occur consquently because of the mutaion are the Eon consuming. Why did Weaker jawed hominds proliferate, what adaptaions occured in thier physialogy with generations living with such mutation. The body of Shaq is good for survival, he makes a lot of money dunking baskets and can provide for his family well, but so does John Stewart.

Enzp
2005-Nov-24, 04:18 AM
I don't disagree with you wayneee, I just thought the discussion above was assuming that of a sudden a new generation was born with an immediate change in brain/jaw ratio. As if a tiny horse jockey turned into a 7 foot athlete.

Mutations like sickle cell are relatively gross things that do show up in a generation. But the gradual transistion from big to small jaw didn't work that way.

Why did evolution select for the smaller jaw? That is the point of the whole discussion. In my humble view, that discussion was wandering off course. Personally I see they correlate, but I don't see that they are necessarily linked or causal. Neranderthals demostrate that hominids can have both large jaw and large brain. SO I don't accept that one made way for the other.

A larger brained being might not need as large a jaw, but I don't think it was a space issue.

wayneee
2005-Nov-24, 04:44 AM
A larger brained being might not need as large a jaw, but I don't think it was a space issue.

I concur

Ken G
2005-Nov-24, 05:54 AM
Mutations like sickle cell are relatively gross things that do show up in a generation. But the gradual transistion from big to small jaw didn't work that way.
I think it did, if it is a single mutation, but I await TheBlackCat to weigh in on the issue, I'm just going by my layman's interpretation of the OP.

Enzp
2005-Nov-26, 02:08 AM
A single mutation? You are assuming there is a gene that can be expressed either as a large jawed small brained creature or as a small jawed large brained creature. There is no one gene that determines this. Many different aspects of our bodies evolved at the same time, and one may make another easier. But many bits of genetic data go into body shape, and many bits go into the structure of the brain. There is not "a gene" for it.

if you have the idea that something large jawed like a baboon one day gave birth to somethiing that looked like Ben Affleck, you are not understanding how evolution takes place.

wayneee
2005-Nov-26, 05:00 AM
A single mutation? You are assuming there is a gene that can be expressed either as a large jawed small brained creature or as a small jawed large brained creature. There is no one gene that determines this. Many different aspects of our bodies evolved at the same time, and one may make another easier. But many bits of genetic data go into body shape, and many bits go into the structure of the brain. There is not "a gene" for it.

if you have the idea that something large jawed like a baboon one day gave birth to somethiing that looked like Ben Affleck, you are not understanding how evolution takes place.
Actualy the article in question refers to a mutation that is still here with us now. The mutation exists, its thier conjecture of the ramifications of the mutation that is in question. No one will argue with you that the increase of brain size took millenia. The Article refered to, theorizes that the reduced skeletal structure needed to support Strong jaw muscle and ligiments would free up the skulls developement structure to allow skull plates to expand. Its an interesting theory to be sure. Since we still have elements of this original mutation, we can see that it indeed belonged to our evolutionary chain of events. Not knowing enough about the human Genome does not help. But we are getting there I assume. As I think about it I like thier theory. Im not saying it did not take millenia and a whole lot of happenstance and whole lot natural selection, and a smidgen of luck to produce Bigger frontal lobes. Yet it is interestiong that we indeed have found a part of the chain of events, in our own back yard (if you will).:clap:

Hugh Jass
2005-Nov-26, 08:01 AM
I'm not sure if I can explain this quite right. One of those things my understanding goes to one point, but not sure if I understand enough to explain in easy to understand terms.
Basically when the term mutation is used, think of it as the ability for evolution to travel in a different direction than it normally would have. A genetic mutation does not normally mean a change in the first individual where the mutation occurs. Take hair color. The mutation that allowed for blonde hair probably occured in an individual that still had dark hair. Several generations down the road, and after this gene had been spread and existed for quite a few years, someone with light brown hair showed up. I think there is a bit of a hang up in terms. Kinda along the same line as theory has a different meaning to scientists and laypeople, mutation has a bit of a different meaning. It doesn't mean the individual, nor some body part is a mutant, just a gene that has something to do with it. The end result may take generations to even give a hint.
A good example might be mink coat patterns. There was a mutation allowing for several different coat patterns and colors some long time ago. In the wild this is not actually seen. You pretty much get the same coat and color patter with very little variety in all individuals. They are brought into captivity and raised, and within 2 generations you have white and light brown and nearly calico fur. Whether it is a function of genetic diversity or some other effect of being in captivity is up for speculation.
The point is the mutation is there, the population is ripe for it to show up, but we just don't see it.
The jaw bone probably stayed hidden for several generations after the mutation that allowed for it, and movement to some easier climate or somplace that changed the diet of the tribe, something along those lines, gave rise to a somewhat smaller jaw. Generations pass and you have a progressivly shrinking jaw. The increase in brain size and capacity may or may not be related. This is speculation as well, reasonable speculation, but oposing views could argue it as being not much more than a SWAG.

Ken G
2005-Nov-30, 01:57 PM
They are brought into captivity and raised, and within 2 generations you have white and light brown and nearly calico fur.
Exactly-- within 2 generations you see dramatic changes that humans would consider to be extremly dramatic if it happened to us! Evolution can occur quite suddenly, and dramatically, when there is a single mutation.

Hugh Jass
2005-Nov-30, 07:01 PM
You kinda missed my point with that. The change from what we see in the wild population to captivity happens in just a couple generations, the mutation *speculation* happened many many many generations ago, and even though there was a mutation allowing for it, we don't see it in the wild population.
Along these lines, I got to discussing this thread with some family over the holiday, and the statement was made that ALL recessive traits are the result of gene mutations. Has anyone else heard this? It sounds plausible to me, but I’d never heard it before.

Ken G
2005-Nov-30, 11:41 PM
But can you give any reason why it was necessary for the mutation to sit dormant for a long time? Is it not obvious that mutations can be sudden and dramatic (and often fatal)? But let me focus this into a single interesting question for those more knowledgeable about evolution than I am:
How did the recessive gene for blue eyes evolve? (assuming blue eyes come from a single recessive gene, if not, pick a different example)

Ken G
2005-Nov-30, 11:42 PM
Along these lines, I got to discussing this thread with some family over the holiday, and the statement was made that ALL recessive traits are the result of gene mutations.
I should have thought that all genes, period, are the result of gene mutations. There must be some other sense to which the recessive genes are being singled out, such as, they are mutations that occur rather late to the gene pool once a species has already been established.

Hugh Jass
2005-Nov-30, 11:46 PM
ISNIP:recessive genes are being singled out, such as, they are mutations that occur rather late to the gene pool once a species has already been established.
:doh:
That more clearly states what I was meaning.::dance:

Hugh Jass
2005-Dec-01, 12:19 AM
But can you give any reason why it was necessary for the mutation to sit dormant for a long time? Is it not obvious that mutations can be sudden and dramatic (and often fatal)? But let me focus this into a single interesting question for those more knowledgeable about evolution than I am:
How did the recessive gene for blue eyes evolve? (assuming blue eyes come from a single recessive gene, if not, pick a different example)

Necessary? No, it's just the way things normally happen, a change is allowed so to speak, but doesn't show up until there is some kind of pressure, like climate, diet, isolation, and after the gene has had ample opportunity to spread through a population. I suppose its possible that there was some dude way back when that popped out and had this drastically different weak jaw, and was somehow able to survive and procreate and pass on his deficiency until brains grew to fill in the space. :confused: Once again, my ability to communicate what I understand is less than my understanding by itself, but typing it out is helping. Basically it is less likely for a mutated gene to be passed on AFTER the physical trait it controls (or helps control) appears, than before the physical change is evident. Eye color is a good example of a change, but a better example might be a horses hoof, that is a single toe. The genes still exist in modern horses showing that they used to have three toes, but the transition was very slow over not just generations, but several progressive species. The outside toes began to shrink and then become vestigial knobs and finally disappear (mostly). The gene to control the change from multi toes to single toe probably mutate long before the recession started, but it wasn’t until other pressures, like probably a move to grass lands and the need to run from predators that the changes started showing up, and in this example, we know from the fossil record it happened evolutionarily speaking quite rapidly.

The significance between this example and the human jaw bone, again if my ability to communicate my understanding could reach what I think I understand, is that what they found is one single gene seems to be responsible for the change. One gene? Not several, this would mean that the change would happen rapidly, but I still don’t think it means weekly world news headlines type changing “Big Jawed Parents Give Birth to Genetic Freak”.

Enzp
2005-Dec-01, 05:08 AM
I don't think you get it yet, Hugh. There is not some large single toe gene that turned on generations ago and is slowly taking over like a balloon inflating. The number of toes didn't change, what changed is the relative size of the toes. Numerous bits of genetic information go into the body shape, not one.

If a gene changes to something, there is no reason to expect it to sit in hiding for twenty generations, until some environmental circumstance ocurs. What happens is some gene enters the pool and a certain percentage of individuals express that gene. When some external pressure starts selecting preferentially for that expression, then the prevalence of it will grow within the population. THAT is how it takes over, not because the gene slowly gains strength. It is because other expressions fade away leaving the one we see now. Unless you mean that metaphorically. I think you meant it literally.

Look at the large prominent jaw of say PAtrick Ewing (basketball player) and compare to the weak jaw of Queen Victoria. Now everyone in between. This whole range of jaw size exists in the current population. If some sort of evolutionary pressure started to select for one or the other, then the overall population would tend to be more like whichever one was selected. If small jaws were somehow beneficial, then the larger jawed individuals would be at a disadvantage and would fade from the population.

Sorry, it has been forty years, what is the word for a prominent, thrust forward jaw? Prognathism?

One interesting theory whether it holds water or not involves our emotions. MAny creatures, including us, love our young ones, our babies. It is wired in us that they are appealing and cute. The theory says that we select mates, or at least find potential mates attractive in part based upon having a somewhat babylike appearance. Babies of many species have relatively shorter jaws than adults. That we find this appealing in babies transfers over to our thoughts about mates. This selects for smaller jaws over time. it may not be the case, but I find it an appealing thought.

Humans walk on their heels, but when you sprint, you run faster if you get up on just your toes. This you would do if you were running from a predator maybe. If you ever wondered why a dog or cat or horse or whatever seems to have a "backwards knee," it makes a lot more sense when you realize that that "knee" is actually the animal's heel. Evolution has selected for the animals that run on their toes over the flat footed ones in those species.

elsewhere:
Why wouldn't recessive genes be mutations? Pretty much everything is a mutation ultimately isn't it? If we look at our ape brethren, we see no blue eyes that I know of. A mutation in the gene for eye pigmentation could cause blue eyes, but only if the whole pair is for the blue. Male pattern baldness, lactose intolerance, myopia, aren't these all mutations?

wayneee
2005-Dec-01, 06:04 AM
Look at the large prominent jaw of say PAtrick Ewing (basketball player) and compare to the weak jaw of Queen Victoria. Now everyone in between. This whole range of jaw size exists in the current population. If some sort of evolutionary pressure started to select for one or the other, then the overall population would tend to be more like whichever one was selected. If small jaws were somehow beneficial, then the larger jawed individuals would be at a disadvantage and would fade from the population.

The jaw size of Patrick Ewing and Queen Victoria , are anthropologicaly the same. Each has the same amount of muscle devoted to the jaw, the same comparitive bone density comparitive to other Homo SApiens. Each have the same ligiment supporrts, and motor control. If Queen Victoria and Patrick Ewing had a love child ( wait a quick laugh) It would just be good ole homo sapien again , with a rather strange life a head of it.

Hugh Jass
2005-Dec-01, 08:27 AM
I don't think you get it yet, Hugh. There is not some large single toe gene that turned on generations ago and is slowly taking over like a balloon inflating. The number of toes didn't change, what changed is the relative size of the toes. Numerous bits of genetic information go into the body shape, not one.

If a gene changes to something, there is no reason to expect it to sit in hiding for twenty generations, until some environmental circumstance ocurs. What happens is some gene enters the pool and a certain percentage of individuals express that gene. When some external pressure starts selecting preferentially for that expression, then the prevalence of it will grow within the population. THAT is how it takes over, not because the gene slowly gains strength. It is because other expressions fade away leaving the one we see now. Unless you mean that metaphorically. I think you meant it literally.

This is basically what I was trying to say as far as preferential selection, the genetic ability is there first and some outside pressure selects for it. The thing is my understanding was that generally a gene entering a pool means a mutation, and the expression of that gene doesn’t occur until it has spread to a certain percentage of the population, enough so that you get individuals with a whole pair for that gene. At that point depending on what this gene controls or helps control the expression may or may not be outwardly very noticeable until you get some pressure selecting for it. So I guess I don’t want to say it is hidden and definitely not lying dormant, just not entirely visible, it still takes generations for some of the end results much of the time.


Why wouldn't recessive genes be mutations? Pretty much everything is a mutation ultimately isn't it? If we look at our ape brethren, we see no blue eyes that I know of. A mutation in the gene for eye pigmentation could cause blue eyes, but only if the whole pair is for the blue. Male pattern baldness, lactose intolerance, myopia, aren't these all mutations?

Not that I doubted it, my reaction was just a little more like, “huh, that certainly makes complete sense, why hadn’t I heard it put like that before?”

For whatever reason I decided to re-read the article and most of this thread a little more carefully, I guess ‘cause you said I didn’t get it, I need to understand what I’m saying not just everyone else. I think I missed something in the article the first time I read it, and subsequently some of the posts that followed. The mutation didn’t directly affect Jaw size, or bone structure. The gene was for controlling the muscle development. A shrinking jaw and increasing brain cavity would both be subsequent developments. So I do suppose in this case it is entirely possible their could be some slack jawed individual, but he still may not have had much of an outwardly different appearance, because it is the type of muscle fibers and their connections.

wayneee
2005-Dec-02, 04:03 AM
development. A shrinking jaw and increasing brain cavity would both be subsequent developments. So I do suppose in this case it is entirely possible their could be some slack jawed individual, but he still may not have had much of an outwardly different appearance, because it is the type of muscle fibers and their connections.
__________________

This is why I had conjectured that diet would have been effected in our Slack jawed fellow. Im sure that the strong jawed were crunching on things that constituted their crucial nutrition. Our Slack jawed might not be able to get its vital nutrition from the cuisine , yet we know it survived. In fact this Slack jaw leads right back to us, so we know it became succesfull. What did this glass jaw do? Did it expieriment with its enviroment in order to find sustanance. Did it need to move and simply lucked out to be in the right place at the right time? What ever happened it lead to survival and further evolution.

Enzp
2005-Dec-02, 06:56 AM
Waynee, the giraffe has the same number of neck vertebrae as something with more conventional proportions like a tapir, yet we find it a distiguishing characteristic. Anatomically, the two example jaws may be equivalent, but they are proportionally different. And while all this range is present in the present population, if some selective pressure were to be added to our environment, the overall averages could shift towards one of those extremes.

SO in that case, (let us say large jaws were favored) large jawed individuals would become more common and small jaws less so. But this would happen very slowly. I make this example to differentiate from a population of smaller jawed individuals all of a sudden producing a line of large jawed fellows that branched off.

wayneee
2005-Dec-04, 07:20 AM
Waynee, the giraffe has the same number of neck vertebrae as something with more conventional proportions like a tapir, yet we find it a distiguishing characteristic. Anatomically, the two example jaws may be equivalent, but they are proportionally different. And while all this range is present in the present population, if some selective pressure were to be added to our environment, the overall averages could shift towards one of those extremes.

SO in that case, (let us say large jaws were favored) large jawed individuals would become more common and small jaws less so. But this would happen very slowly. I make this example to differentiate from a population of smaller jawed individuals all of a sudden producing a line of large jawed fellows that branched off.


I red your post , then reread it , and unless Im missing your point , I would say we agree.:lol:

Enzp
2005-Dec-06, 06:07 AM
As I see the (potential) disagreement, you are saying that the broad range of variation in humans is morphologically equivalent because they are point by point equivalent parts. WHile I countered that there is also a point by point equivalence between the neck bones of a giraffe and its cousin the tapir (Not to mention many other mammals). My point being that the equivalence of parts does not evidence That two samples are or are not the same species even.

Perhaps it is I who does not get your point rather than the other way around.

Hugh was positing that a sleepy gene was waiting to eviddence itself, and I was suggesting the range of variations would be seletively advanced, rather than a gene taking over after a delay. In other words there was never a giraffe gene amongst the tapors waiting to express itself, there were only tapirs with slightly longer necks selecting in some population to the point they became a separate species. So in the Ewing/Victoria case, there was no Ewing gene waiting to take over, there was just the whole range of variations that was going to be (hypothetically) selected from.

Perhaps I misconstrued your earlier post as disagreement. For better or worse I am trying to disabuse Hugh of the sleepy gene notion.