The jaw of Teinolophos trusleri catches the ear bones in the act of separating from the jaw.
Posted on 02/11/2005 6:49:09 AM PST by PatrickHenry
Triple bone structure arose independently in platypus and humans.
Listen up: mammals seem to have evolved the delicate bone structure of the middle ear at least twice. The surprising discovery comes from a fossil, found off the southern coast of Australia, that belongs to an ancestor of the platypus.
Modern mammals are unique among vertebrates for possessing three tiny bones in the middle ear. The malleus, incus and stapes (commonly known as the hammer, anvil and stirrup) work as part of a chain that transmits sound towards the skull. Birds and reptiles have only one bone to perform this function.
Because the mammalian arrangement is so complex, scientists believed that the set-up had evolved on just a single occasion, in an ancestor that gave rise to placental animals (including humans), marsupials and monotremes (such as the duck-billed platypus).
All this changed when James Hopson, a vertebrate palaeontologist at University of Chicago, Illinois, took a trip to Australia. There he met a team of researchers including Thomas Rich of Museum Victoria in Melbourne.
The jaw of Teinolophos trusleri catches the ear bones in the act of separating from the jaw.
Rich and his colleagues had recently unearthed a fossil of Teinolophos trusleri, an ancestor of modern monotremes that lived 115 million years ago. "He said he had some new Teinolophos specimens and when he showed them to me I almost fell off my chair," says Hopson, an author of the study, published this week inScience [Rich T. H., et al. Science 307, 910 - 914 (2005)].
Hammer time
Palaeontologists believe that the middle-ear bones of modern mammals once belonged to the jawbone and later separated to adopt their present location. This is supported by the fact that the middle ear's bones associate with the jaw in the early development of modern mammalian embryos.
What makes theTeinolophos specimen surprising is a large groove in its adult jawbone, which indicates that the smaller bones had not yet detached.
Teinolophos lived after monotremes split from the placental and marsupial mammalian groups. Its jawbone structure, along with its place in the evolutionary tree, hints that a common ancestor to all these mammals lacked the special three-bone ear structure.
This means that natural selection must have driven the same rearrangement in independent groups, after the monotreme split. "Some embryologists had the idea that it might be convergent but nobody really believed this," says palaeontologist Thomas Martin of the Senckenberg Research Institute in Frankfurt, Germany. "I was quite shocked when I heard that such a complex morphological transformation happened twice."
The discovery will compel many experts to rethink their appreciation of mammals' common evolutionary heritage. "Until now it was considered to be one of the most important shared derived characteristics of modern mammals," says Martin.
You've moved into the realm of philosophy...don't be surprised if someone proffers you a philosophical answer.
monotremes rule
"...how an insectivorous quadruped could possibly have been converted into a flying bat, the question would have been far more difficult, and I could have given no answer." Origin of Species Ch6.
His solution: "Yet I think such difficulties have very little weight." loc cit.
Fallacy of exclusion anyone?
There's no other way to respond to Design advocates. You can't argue science against the inherently unscientific.
AHhhh....
I get the point..........
Oh yes; of COURSE he does!!!
(Now; how do I post a picture of ME?)
Have you met my EX?
(You left out James Caan in MISERY)
"Okay, I'll buy that...but what causes the process to happen? Is it slight inaccuracies in gene transfer at meiosis?"
Several:
1. Primarily, mistakes in DNA replication (for animals and plants this has to be in the germ cell line). If you are not familiar read the history of hemophilia in the royal households of Europe, all began by a mutation in one of Victoria's eggs.
2. Natural mutagenic things - cosmic rays, chemicals like polyaromatics, mutagens in your food, radiation, UV light, etc. (I know these are mutagens, but they still are "natural").
Also...what does it take to get a population of animals that are cross-fertile with one another, but no longer cross-fertile with other descendants from their ancestral line?
Physical separation for one, but I will have to defer to others for other answers.
Phooey on the platypus!
I want to know why homo sapiens was SO much better at survival no Neanderthal are still around...
Maybe, maybe not. The evolution of the bat isn't terribly hard to understand. There were certainly conditional steps along its evolutionary path -- see the advantage that flying squirrels, for example, get from having a web of skin even though they don't actually fly.
I would think Victoria was a bit young to be responsible for the hemophilia in the Romanovs...but of course I could be wrong.
More to the point, hemophilia isn't a useful adaptation. It doesn't contribute to survival. (I know that you weren't claiming it was; you were making another, quite valid point.) All of the mutations I've ever heard of in humans are actually detriments to survival, causing conditions like cystic fibrosis, hemophilia, beta thalassemia, or Down syndrome. When was the last positive, advantageous mutation in humans? Shouldn't there have been one in recorded history?
If Asperger syndrome turns out to be due to genetic causes, and it probably will, that may be our one. Geekdom is a survival advantage. It may, however, give up in reproductive success what it gains in survival. =]
You obviously don't read these threads very much. Its generally the young-earth creationists that insist on an either/or dichotomy. We're often chided that a theistic evolutionary worldview is not a valid Christian outlook. It's mostly evolutionists who insist that evolutionary biology is silent on the subject of God and that it is a perfectly defensible position to accept both. The inevitable knee-jerk response from the holy warriors is that if you deny the literal historical truth of Noah's Flood and the week-long creation event in Genesis, then the Bible canot be considered God's word.
Evolutionists as so much fun. Darwin's admitted challenges are explained away with spin along the Markov chain. Then the platypus attacks, and someone morphs a hippo and a whale...
Evolution says nothing of the sort. It says it must happen, that's all.
has to be beneficial
Not necessarily. So long as it doesn't kill the individual in the current environment, it can be passed along to future generations.
has to be so beneficial that it confers a significant competitive advantage on its offspring
Usually mutations are neutral. In most cases a currently living organism would hardly be affected. There may come a time, however, when a future environmental change will make the mutation beneficial and it will become fixed in the population.
must be expressed in a dominant allele that is not erased or corrected by the female's allele (most mutations are recessive)
Most speciation occurs in geographically isolated populations. In such populations, typically inbreeding occurs, making it more likely that an unexpressed mutation in the first generation will be expressed in a future generation. This argument also reinforces the notion that most mutations are neutral, since most of the time, they aren't expressed in the organism in which the mutation takes place or in its immediate descendants.
Then any offspring with the beneficial mutation must ultimately be exposed to all of the other elk from all of the other nearby herds where more dilution will occur. And all of the non-mutated elk elsewhere must die off -- otherwise the species hasn't evolved at all -- you'd simply have dark brown elk in one place and light brown elk in others.
As stated above, speciations tend to occur in populations that have become geographically isolated from a parent population. In such populations, recessive mutations that occured in past generations of the parent population have an increased chance of being expressed and being selected for (or against). Eventually, given enough generations of the isolated population, this population will be genetically different enough from the parent population to prevent interbreeding (hypothetically, since the populations are isolated from one another). There's no reason why the parent population must become extinct in all of this.
Now tell me how a super dog emerges from my scenario?
A super dog is never guaranteed to emerge. One of three things will happen. Either the dogs in the new environment will evolve to become better suited to that environment than are domestic dogs, the new environment will prove to be not sufficiently different from the old one to cause any major changes to the dogs, or the dogs will be incapable of dealing with the new environment and will become extinct. I'm not sure what you mean by a "super dog," but you seem to be making the fallacious assertion that a newly evolved species must be more complex or more advanced (whatever these vague terms mean) than the original. All that is really true is that the new species will be better suited to surviving and reproducing in the environment in which it arose. A change in that environment could make that new species inferior to the old one, even to the point where the old one survives and the new one becomes extinct.
Except for These guys. They must not be paying any attention to you or your sources.
Sickle cell trait is actually a mutation that conferred a survival benefit to humans who had it, at least in a specific environment, namely an environment in which malaria is prevalent. In homozygous individuals it is harmful, but in heterozygous individuals it gives increased resistance to malaria. Remember, beneficial is not an absolute term, but rather is relative to the environment. Also remember, harmful and beneficial are relative only to reproductive success. A hypothetical trait that always caused death in humans between the ages of 40 and 50 would be considered a neutral trait in evolutionary terms, although a person affected with it would certainly not see it that way.
I can see that...but the appearance of the mutation is prehistoric. We can presume that it first appeared in a single individual at a fixed point in time, but that (admittedly compelling) presumption isn't the same as being there and documenting when the mutation appears.
Others have supposed that the pronounced tendency of certain native american populations to Type 2 diabetes is also a survival adaptation, namely to periods of famine. Again, I can see it, but also again, it's not the same as being there and watching it happen.
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