Evolving the Musculoskeletal System

Well, the glib answer is that they're frequently not all in the right positions (these aren't from the same individual):The quick answer is that there's clearly a pretty substantial survival advantage to having functioning limbs, so the genetic and epigenetic limb development program is obviously very highly conserved.The long answer is that cells work together to match skin to muscle to bone. Bone cells say "grow from this end to that" to muscle cells. Muscle cells say "cover us" to epithelial cells. Genetically, limb length and development isn't a coincidentally-synchronized series of separate programs; there's one genetic program that determines limb development by determining the rate, order, and extent of bone lengthening.The proof of this is the phenomena of achondroplasic dwarfism:Achondroplasia is caused by a single point mutation that changes one amino acid in the protein FGFR3 (fibroblast growth factor receptor 3), a transmembrane receptor protein in collagen-growing cells (fibroblasts) that results in the receptor being constantly "active"; fibroblast growth factor is a negative regulator of cartilage formation, so individuals with achondroplasia never experience normal bone elongation.As you can see, though, achondroplasiac dwarves have limbs with muscle and skin appropriate to the shortened size of their bones; their muscles and skin don't grow any longer than their bones even though they have completely normal genes for muscle and skin growth.This proves that limb growth is not as you construe it - it's not a matter of separate genetic programs producing skin, muscle, bone, nerves, and circulatory tissues that all just so happen to be the right length to fit together; the tissues are coordinating their growth by means of signalling hormones, following a program of growth determined entirely by the skeletal system. Because gross deformities in skeletal structure are usually fatal, organisms evolved a fairly high accuracy in terms of constructing their own bodies. Of course, when something goes wrong, spontaneous abortion is usually the result, so you don't see living examples of organisms with the wrong sort of joints.Frankly the more necessary something is for an organism to live, the easier it is to imagine it being the result of random mutation and natural selection, because there's such an obvious selection pressure against ill-formed organisms.

Natural selection against ill-formed individuals explains why, for the most part, organisms are well-formed. I've posted some examples of people with bones in the wrong place, bones that did not follow the appropriate plan of growth, and so on. Skeletal deformities are quite common. Here's some more examples, individuals who were exposed pre-natally to s-thalidomide, a compound that intercalates DNA and inhibits synthesis of hormone growth factors such as IGF and FGF, which inhibits limb bug formation due to suppression of vascular growth:As you can see, despite the fact that limb growth is truncated only by suppression of vascular tissue (which bones need to grow), these individuals don't have long "empty sleeves", normal-length limbs with truncated bones. They have truncated muscles and truncated skin to match their truncated bones, because limb growth is primarily a phenomenon where bones grow according to a genetic program and muscle, skin, nerves, and vascular tissues grow to match.That's why your muscles frequently ache during puberty; your bones are extending and your muscles get stretched, damaging them, and they have to grow to match, just as if you had worked out. I have stretch marks across my back from the time I grew about 7 inches in a single summer (but I tell people they're from the time I was lashed in Russian prison, it's a better story.) The femur, pelvis, and bones of the ankle all grow from individual osteoblasts. They're not a single bone because they're never a single bone at any point in your life.

Ask a cripple. What do you think your chances of outrunning a cave bear with a clubfoot are? Because not having the proper joint in the proper place is a significant disadvantage. Someone with a saddle joint between the femur and the pelvis isn't going to be able to stand, much less walk. Immobility is a significant survival disadvantage.

I thought I showed you the false starts - the individuals with deformities, the achondroplasiacs, and so on. The "false starts" are the individuals whose skeletal systems didn't form according to the conventional program, but whose deformities were not so severe that they didn't simply die in the womb.If you mean something else by "false start" then you're going to have to be more specific. Well, achondroplasia isn't damaging to the organism, per se. Are you aware that individuals with dwarfism have incredible physical strength, due to the shortened moment-arm of their limbs and therefore the increased mechanical advantage?I mean, they're just short. They live just as long as you or I. Humans evolved in the tall grasses of the African savanna, so there was a selection pressure for being able to see distantly over the weeds, but it's not hard to imagine a selection pressure against height, in favor of a small, sturdy, compact body. In that case we'd be considered the mutants (not least of which because the normal gene, which you or I have, is recessive.) If you want examples of observed beneficial mutations you should start here: Are Mutations Harmful?

Inference is something you do with evidence. Then by all means, explain why. We don't only have inference. We have a record of past mutations that exists in the genome of every living thing. A human with a ball joint knee instead of a hinge knee wouldn't be able to stand, because the knees would simply pop out to the side. You don't have the muscles in your knee to restrict that kind of movement without the assist of a joint that simply won't flex in that direction. "Kinds" are not something that we have ever observed in the "true world of observable science." "Kinds" are not a description of biological reality, they're a fabrication by creationists who don't know anything about biology. The proof of this is that creationists cannot define "kinds" except circularly.What a surprise, though - 40 posts in and you're already scrambling to change the subject. I think we're all going to conclude that your extreme haste to change the subject from musculoskeletal growth to "created kinds" is because you found that, once again, biological science had ample answer to your supposedly "unanswerable" questions.IC - is it ever going to occur to you that the reason these questions seem "unanswerable" to you is because you don't know enough science to understand the answers? Why do you continue to pretend that you can engage in criticism of a field that you do not evince even the slightest interest in actually learning about?Don't you see how, at the very least, you're at a tactical disadvantage when you allow yourself to be the person in these discusssions who knows the least about biology? I was kind enough to suggest an entire curriculum of study about DNA and mutations to you (a kindness that, in typical Christian fashion, you repaid with disgusting invective.) How did that go for you? Did you even bother, or did you decide that knowing nothing at all about biology would somehow give you the advantage you need to go toe-to-toe with evolutionists?How, exactly, is that supposed to work?

But it is proven. Remember? Last week I recounted the experiment that I performed myself that proved it. Remember how you had no response and retreated, thus conceding the point? Sure. Proving the existence of random mutation and natural selection is such a trivial task we let undergrad biology students do it. You can do it, too, if you can get your hands on some Ames strain E. coli. (Your local biology supply catalog will have some you can order in the mail, usually a lyophilized culture you'll have to re-hydrate on your own.)Of course, that would require you to be someone of intellectual curiosity and honesty, not an intellectual coward desperately trying to ignore the evidence of his own eyes to maintain a cherished ideology.

No, I merely restored a disabled metabolic function in E. coli by means of natural selection and random mutation. If random mutation did not occur then my Ames bacteria would not have been able to grow on minimal glucose media. But they did. By means of random mutation - which you're asking us to provide evidence of.Which I have. Why would a bacteria need a spleen? You're not making any sense.

Do you think that different amounts of knowledge could justify different conclusions? That, say, a few facts taken out of context might justify one conclusion, but the entire suite of facts might justify another?If that's the case - and I think a reasonable person would have to conclude that it was - don't you think that one has a duty to, and an interest in, making sure that their conclusions really are justified by the largest amount of knowledge possible?You and I seem to agree that you don't know all that much biology. I'm just trying to get at why you think that's a strong position to argue from. The most amazing thing about the theory of evolution is that it is so common-sensical. In a given species there really are more individuals born than will, or even can, survive to adulthood and reproduction. Individuals really do significantly vary amongst themselves in ways that are advantageous or disadvantageous to survival, and they really do pass on those traits to their offspring if they survive to have any.That stuff is all just so amazingly obvious and common-sensical that it continues to amaze me that anyone could be a creationist. Denying the power of random mutation and natural selection to effect species change is basically saying that all members of a species are exact clones of each other, offspring aren't any more like their parents than they're like anybody else, and that when a fox catches a hare and eats it, it's not because the hare was slow, he was just unlucky.And none of that is true at all. Everybody knows none of that is true, but that's the world where there's no such thing as mutation or natural selection.

Who ever said anything about a new system or organism? I told you, the experiment is proof that random mutation and natural selection exist. Who ever said that "all that happens is what happened during my experiment"?

That's great, and thanks for once again needlessly impugning my intelligence, but that's not at all what I asked, is it? Nobody was talking about intelligence, we were talking about knowledge.But, you've pretty clearly articulated your standpoint, which is that you believe that increased knowledge doesn't illuminate issues, it simply confuses things to know more, and therefore a complete neophyte in any field is the only one who is going to be able to accurately apprehend the truth.Would you say that's accurate?If so why are you here asking questions? Doesn't asking us questions simply expose you to the danger of learning something that would, from your perspective, simply obscure the real biological truth that you're able to see, unencumbered in any way by an opaque weight of formal knowledge?Help that make sense to me. If learning and knowledge is so antithetical to truth, why are you asking us questions about what we know? Your questions aren't going to make us forget what we know, but they might expose you to new information. Isn't that incredibly dangerous for your continued ability to see what is true? Well, sure. Help me understand Percy's approach. Here's his most recent advice to you:

quote:

---

If I could make a point again that has often been made before, you don't have to accept evolution to understand it. But you do have to understand it before you can make criticisms that make sense. Otherwise you might end up endorsing a wrong-headed post from Bolder-dash.

---

And here's the remarks by me that you apparently found so "arrogant" that they made you ill: I'm certainly more direct than Percy but the sentiments being expressed, here, would seem to be exactly the same. I thought the last bit, especially, would be particularly helpful to you. Can you (or Percy, for that matter) explain how what he's saying is somehow more palatable than what I said?Edited by crashfrog, : No reason given.

Why do you think you need bones to have nerves? What exactly is the "issue" here that we're sweeping under the rug?The fact is that we can survey the animal (and plant and microbe) kingdom and see primitive versions of all of those systems all over the place. A fully-functional human being does not represent the minimal level of complexity and interconnectedness necessary for life - not even close! There are innumerable ways our systems could be simpler, less complex, less full-featured - and that's how they evolved, in a long, winding path through all those simpler states. Why is it "dumb"? Try to argue the position, not the person. Granted, I'm an incredible idiot. Could you be more specific about how I'm wrong?

Agreed, but that's not what I asked. Surely someone so smart is a much better reader than that?I asked why you think you need to have bones in order to have nerves. Do you think that organisms with no bones - earthworms, let's say - have no nerves at all? I did, in three posts in this thread alone, to which I'm awaiting your reply. Anyway, why are you asking me to do it if you're so sure I'm such a risible moron?Could it be that there's something you want to learn from me, after all?

You're free to reply or not reply to any of my messages as you see fit, and you always have been. I suspect that this is simply what you say to people who have been so effective at rebutting your arguments that you literally don't know what to say. Well, you said it in message 71:

quote:

---

Besides the over 1200 components briefly mentioned previously, we also need to acknowledge all the other systems that directly support the Musculoskeletal system and in fact could not exist without the following;
The Neurological System; The Respiratory System and The Circulatory System...

​

The FACT is my friend, every system within our bodies is dependent on each other for survival.

---

So, exactly in what sense is it a "FACT" that our nerves are dependent on our bones for survival? All organisms are under evolutionary construction, at all times; all systems are "incomplete" compared with the functions they will gain in the future.But if you wanted to see an organism surviving with incompletely-developed bones, muscles, skin, and nervous systems, you need look no farther than the nearest pregnant woman:

Earthworms have blood but no bones. How do you explain this discrepancy with your "FACTS"?Or is this just about how I know so much more than you that I can't see "the truth" that no organism without bones could ever possibly survive or exist? These organisms are independent, once they're born. But an organism's systems don't develop during its independent adulthood, they develop during its gestational period, in egg or womb, as the organism follows a genetic program of development. If an organism hasn't completed that program of development then it either hasn't been born yet or has died (and been expelled from the mother, if that's relevant.)If you want to know how an organism's organs and systems develop, then you're necessarily looking at the prenatal, gestational phase of the organism's lifestyle, because that's where evolutionary changes to body plan and function by genetic mutation are actually enacted. You've taken into your mind the deluded notion that I'm trying to make fun of you or make you feel stupid. Nothing could be further from the truth - I'm trying to share my knowledge with you. The fact that you continually spit into my outstretched hand is disappointing, mystifying, and (if I may) does not speak well to your character.

Well, as I answered you before, that was is Message 71 when you said:

quote:

---

Besides the over 1200 components briefly mentioned previously, we also need to acknowledge all the other systems that directly support the Musculoskeletal system and in fact could not exist without the following;
The Neurological System; The Respiratory System and The Circulatory System. And lets not overlook that little thing called the Brain.

​

The FACT is my friend, every system within our bodies is dependent on each other for survival.

---

Yet, there are an abundance of organisms that survive very well despite a total lack of skeletal structure. "Change goal posts"? The subject of this thread is the musculoskeletal system, which did not evolve de novo in every organism in which it appears. The human musculoskeletal system was inherited by descent with modification from the evolutionary ancestors of human beings, which themselves inherited the system from their ancestors and modified it, and so on.If you want to talk about the evolution of the musculoskeletal system itself you're necessarily going to be talking about organisms much, much older, and simpler, than Homo sapiens, or any mammal for that matter. That's going to necessitate looking at organisms that have primitive musculoskeletal systems, or lack it altogether. LOL!