Gene MYH16: A Tasty New Jawbreaker

kid_wonder writes "Jeremy Roenick take heart! Glass Joe take heart! Scientists discovered that humans owe their big brains to a single genetic mutation that weakened our jaw muscles about 2.4 million years ago. So I guess now we can call all those dopey muscle bound guys 'apes' with a clear conscience."

Comments

Actually, no.

[Romothecus]

RTFA. Virtually every scientist who read their work was of the opinion that the explanation "mutation to smaller jaw means bigger brain" is incredibly simplistic and that the real explanation is probably far more complex. The change in jaw morphology is probably only one of many contributing factors.

"Discovered"?

[afabbro]

"Discussed a new theory" is more accurate...

Re:"Discovered"?

[bugnuts]

Stop calling everything "theories" as if that word weakens the probability of it being true. That is the same lame tactic used by Creationists.

Theories are developed hypotheses, that have withstood scientific examination. Some theories are stronger than others, such as evolution, which has extremely compelling and a wealth of strong evidence. Examining genes and doing the statistics on them is also extremely compelling. Everything you do with technology including the computer you're using now is supported completely by theories. Does that mean it's not true? Kind of like disproving Zeno's Paradox -- please stand in front of the arrow.

So, sure, it's a theory as opposed to a proof. But you can probably bet your life on it.

Re:"Discovered"?

[Ayaress]

I'm pretty sure I've posted this exact reply to the exact parent a dozen times over.

In science, Theory is the highest level of understanding. Law and observation are, in fact, much lower on the heirarchy.

Observation is dumb: It's just what you see. "Oh, the sky is blue." "It hurts when I hit myself with this rock." "Look, there's another rat." That's observation.

Law is also pretty dumb. It's just a set of rules derived from observation. e=mc^2 fits observation, and it has some interesting connotations, but it doesn't say anything about WHY the equation works, and it says even less about HOW matter and energy are interchangeable.

Theory is an overarching collections of observations, laws derived from observation, and principles deduced from laws.

Theory explains why laws work, and why observations are as they are.

To be granted the distinction of 'theory' an idea must:
1. Explain any and all laws and observations already explained by a previous theory (example: to be valid, Relativity had to encompas Newtonian mechanics);
2. Explain such in an imperical manner (any forces involved must be identified and observed. This is why there is no theory regarding dark energy and dark matter - they have yet to be identified, observed, or quantified);
3.a. Explain something not covered in the existing theory (Darwin's theory explained why rats with their tails cut off did not have tailless offspring, as Lamarck's theory said they shoudl);
OR
3.b. Explain the existing theory in simpler terms (such as the replacement of phlogiston theory and epicycle theory by their more advanced, but much simpler, successors).

Now, by calling an observation a Theory, you are, in your misguided attempt to discredit it, in fact exaulting it to a much higher status than it claims to hold already.

Re:"Discovered"?

[Smidge204]

I think the parent was commenting on how many people disregard ideas that are not compatible with their views (eg: Creation and Evolution) by saying "it's just a theory".

A "theory" is usually given much more weight than a "belief", because theories are typically based on observation and experimentation, reviewed by peers, and have been used to make accurate, testable and verifiable predictions. Beliefs tend to be more based on emotion and hearsay. It is therefore reasonable to assume that a "theory" is closer to reality than a belief, if only in a practical sense.

Moreover, theories are seldom touted as absolute facts, and most credible scientists will admit their theory wrong/flawed when given sufficient evidence.
=Smidge=

Re:"Discovered"?

[b-baggins]

This isn't even a theory. It's a hypothesis. It requires experimental verification before you can call it a theory.

Re:"Discovered"?

[RevAaron]

Indeed. I hate it when people say this or that (usually "evolutionism"; -ism, heh) is "just" a theory. A theory is a big deal. Perhaps creationism is "just" an educated guess, but the definition of the word theory is not. In common usage, people use the word "theory" to mean just that- an educated guess, rather than a hypothesis backed up by a lot of evidence.

And no, like you say, it's not a proof- but proofs really only exist in the world of mathematics. No scientist can say that a particular theory is 100% proven, ever. That is science, and the fact that science can adapt and grow with new information is one of its great strengths.

*sigh*

Re:"Discovered"?

[bugnuts]

This theory could be true, or it could equally not be true.

Wrong. Simply because there are two choices between true/not-true, does not give it 50% chance of either.

There are theories you bet your life on, every day. If they all had an equal chance of being true or false, you would be dead now. Try flipping a fair coin 100 times and getting all heads. Is there a chance you can do it? Yes, but is it likely? No.

He calls it a theory rightly, and it does weaken the probability of it being true.

You know nothing about probability. He could call it a yellow elephant with handlebars, but that doesn't affect the probability of it being true or not. But he would want you to believe that.

It is a theory, rightly, but he does not call it a theory rightly. He calls it a theory as if that somehow makes it less likely to be true. They're all theories and all scientists know this, but he was simply using misleading rhetoric and calling it a theory wrongly.

Re:"Discovered"?

[joebok]

By way of example, one of the axioms is that parallel lines never meet. We don't actually know if that's true, but it's pretty close. If we do turn out to live in a curved universe, we'll have to throw away some bits of maths.

You are correct that math and logic require basic unproven assertions that "nothing is provably 'true' on its own merits". But math is not about truth. No piece of math will ever have to be thrown away!

Geomoetries in which the parallel postulate you mention are different than the Euclidean are just as consistent and logical as those with different ones. They can even be useful:

If, given a line and a point not on that line, you have exactly one line through that point which is parallel to the first, you are dealing with a Euclidean plain. Architects and Engineers love this one. Alternately, if there is more than one line through that point parallel to the first, then we are in a hyperbolic space. Physicists and Astronomers tend to like this one, but whether the universe is Euclidean or hyperbolic it does not in any way invalidate these geometric notions. In fact, if you take the axiom where there are NO parallel lines you are in a "spherical" geometry which is really handy for navigation.

Silly protozoa!

[Jerf]

Silly protozoa, if only you had known that this one gene would be responsible for super intelligence, you could have mutated billions of years ago and beats humans to the punch!

What? You say you're missing thousands of other necessary genes and you can't assign responsibility for such large changes on one single change? However will I then write misleading science stories, and even more misleading Slashdot article intros?

That's not bad commentary, for a protozoa. Pity the article author isn't that smart.

Re:Silly protozoa!

[Otter]

What? You say you're missing thousands of other necessary genes and you can't assign responsibility for such large changes on one single change?

It's not obvious to me that your spin is more correct than his, though. Does a single mutation take you from a chimp to a reality show contestant in one jump? Of course not. As you say, there are thousands of other changes involved.

But what's being proposed here is precisely that a single mutation radically changed primate head morphology and changed the selective constraints on all those other intelligence-enhancing mutations. Is it true? Who knows? But that does seem to be what's being argued.

Re:Silly protozoa!

[drinkypoo]

Does a single mutation take you from a chimp to a reality show contestant in one jump?

Arguably, you don't need to have any mutation to go from one to the other. The two are generally freely interchangable.

Especially on Fox.

Good news for Louisiana

[bugnuts]

Slack-jawed yokels have bigger brains!

Uncertain cause and effect

[Chilltowner]

While it's true that Australopithecus species had much smaller brains than anatomically modern humans and other of the Homo genus, this isn't the gene that separates us from the apes--earlier species made that division.

It also seems to me that they may be putting the cart before the horse here. Depending on the feeding habits of our Homo genus ancestors, a smaller jaw could be a decidedly large disadvantage, limiting the kinds of foods that could be eaten by a scavenger species such as our ancestors. It seems possible, and even likely, in this case, that our already advanced brains provided a large enough offset against the loss of powerful jaw muscles. This might mean that we were well on our way toward advanced thinking before the loss of muscle mass in the jaw.

Anatomical structures always pretty tricky, especially when it comes to judging cognitive development and other tangential related adaptations. The kinds of mutations that make us human (smaller jaws, larger heads, versatile voiceboxes) also tend to cause of a lot of potential problems (restricted diet, difficult birth, tendency to choke). Weighing the value of one change over another become enormously difficult.

Not to knock their work, though--this is pretty amazing stuff and will definitely be another piece of the puzzle for anthropologists to consider. My only concerns are that we not look at this as a) the great divide between us and the other apes or b) the silver bullet that made us the brainy folks we are today.

Re:Uncertain cause and effect

[Ayaress]

It seems possible, and even likely, in this case, that our already advanced brains provided a large enough offset against the loss of powerful jaw muscles

Take a look at most simain brains. The jaw muscles of a chimp, gorrilla, or even an Australopithescene, attach at the very peak of the skull, and are very thick, comprising the bulk of the head.

There's just not room to expand the brain with ape-like jaw muscles. You're right on one thing, though: Weak jaws are a severe handicap without expanded brains.

There are three ways the two changes could have come: Brain, then jaw; jaw, then brain; both in parallel.
The brain can't expand against simian jaw muscles, so the first one's out.
Weak jaw and small brain are a severe handicap, and the remaining strong-jawed humans would have outcompeted their slackjawed relatives, and the weak-jawed strain would have been bred into extinction.

However, both simultaneously makes the transition profitable and possible, but you're ignoring something important: Related growth rates.
Just the act of lowering the point of connection of the jaw muscles (in the case of apes, this is a ridge on the very top of the skull - in the case of humans, it's the top of the temples, just behind the eyebrows) makes the braincase of the skull larger.

Re:Uncertain cause and effect

[Chilltowner]

Excellent points!

The problem I have, though, is that the article implies that the weak jaw is the result of a single mutation (or a small cluster of them). This would seem to point toward a very "punctuated" change in the strength of the jaw. The fact that it didn't do us any harm in the long run could indicate one of several things:

1) the environment we were living in didn't require us to chew the kinds of plants that simians did (and do). Weak jaws were not maladaptive.

2) it was better to be able to chew on plants that required a more simian jaw and dental arcade, but our brains carried us through. Weak jaw is potentially maladaptive, but less relevant.

3) weak jaws were maladaptive, but other parts of our morphology (e.g. the attachment point of the muscle, different kinds of teeth) soften the blow long enough for the benefit of a weak jaw, larger potential cranial capacity, to come to the fore.

I don't pretend to have the answer to any of this, but I think a lot these points support my main idea: the gene is not the silver bullet. There are other anatomical issues that have to resolve themselves before we get to modern humans (narrowed, flattened zygomatic arches, change in placement of key muscle anchors, smaller cheeks, reduced protusion of the lower face) as well as the onset of "culture"--i.e. at what point did habilis/rudofensis start using handaxes and other tools to the point where teeth were far less important to our survival than they might otherwise have been. Was there a "perfect storm"? Did we suddenly have weaker jaws at the right point where we could replace teeth with tools?

We also have to figure out which of the Australopithicines was our ancestor--the more gracile species or the robust (which have the very large muscles you pointed out, extending up to the crest of the skull). That would impact on the severity of the change between this ancestor and the genus Homo.

It's really fascinating stuff, and this discovery will probably play an important role in how we imagine the crossover from the Australopithicines. But, like I said, there's a lot more work to do and a lot more that needs explaining. There is no silver bullet, and I think the researchers would agree with that. The media, on the other hand, will probably stick to the hype--they seem to like simple, gene-based explanations these days. Ultimately, though, the question will be resolved by a confluence of ideas from geneticists and the stones-and-bones folks.

Re:Don't buy into the hype

[Ayaress]

Yes, but this comes down to the constant issue with any scientific literiture. There are several versions of every story:

1. What the scientists actually think (what I was addressing in my post).
2. What they tell the people they get their grant money from (to make it sound more profitable)
3. What the damned journalists say when they get ahold of it.

For example, take last week's discovery of sediments on Mars precipitated from salt water:

1. What NASA thinks: "Well, there's the proof of the sea we were looking for. Pity it's not there anymore"
2. What NASA says: "Hey look at this, there used to be water on Mars! And water doesn't just disappear, you know. Imagine what could be done with that much water!"
3. What the journalists say: "OMG OMG OMG TEHER WERE LIFE ON MARZ OMFG!!!111oneone"

Apes

[AllenChristopher]

"The conclusion that this mutation was responsible for the divergence of humans and apes is just plain wrong."

It's just plain wrong in another way. Humans are both apes and primates. The divergence is rather far down the taxonomic tree. We and our proto-human relatives are in sub-family Homininae, as distinct from the other members of Hominidae. The Hylobatidae are also apes.

"Theory" is a hard concept to teach

[cagle_.25]

My students always have a mental block when it comes to teaching the distinction between theory and law. Although I state clearly several times that a "law describes, and a theory explains", many students have it firmly fixed in their minds that the progression of the scientific method is

Observation --> hypothesis --> theory --> law

instead of the correct

Observation --> law --> hypothesis --> theory

By the middle of the year, when we start talking about Boyle's Law and other gas laws being explained by the Kinetic Theory, some students start to get straightened out.

I'm not sure why this is so difficult for them, but my hypothesis is that it has something to do with their underlying thought structure. The reason (I believe) that students believe that theory comes before law is that they themselves have trouble distinguishing what they SEE with their BELIEFS about what they see. Therefore, they see no need to distinguish laws from theories. My $.02