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.
Them suckers MUST have had a tough needle-beak, to penetrate that tough lizard skin before us soft mammals showed up.
The gradient was caused by interbreeding. I will agree with that. However, it still is a case where allele frequencies have changed over time, and hence is an example of human evolution, regardless of cause.
Platypus and science ping.
However, not all locations receive equal amounts of energy from the sun, which is the important factor. That's why some places have warm climates and some have cold climates. It's not the number of hours that the sun shines that controls skin color evolution, it's the amount of solar energy that's received.
And I still can't compare the teeth in the pictures. But note that modern hippos have big sharp teeth.
Interbreeding with what?
Humans spread out over the world, probably from Africa where they were dark. As time went on they grew lighter in the northern areas.
Maybe after the races were formed there was interbreeding, but prior to that it was evolution. You can't have "interbreeding" if everything is the same.
The same thought is true when the literalists claim three races came immediately from the same family.
Little dinosaurs probably had softer skin – plus there were little mammals, birds etc.
Mosquitos feed for energy on plant nectar. Only the females bite and suck blood.
Humans have hair not fur. Stremba has addressed your misunderstanding of sunlight. I would add that the reason Vitamin D is so important is because of infant mortality in either too high or too low a concentration. Thus, a small difference in mortality selects for skin color. It does not take much advantage for natural selection to work.
"Jablonski and Chaplin note that when human indigenous peoples have migrated, they have carried with them a sufficient human gene pool so that within a thousand years, the skin of their descendants living today has turned dark or turned white to adapt to fit the formula given above--with the notable exception of dark-skinned peoples moving north, such as to populate the seacoast of Greenland, to live where they have a year-round supply of food, such as fish, rich in vitamin D, so that there was no necessity for their skin to turn white to let enough UV under their skin to synthesize the vitamin D that humans need for healthy bones.
In considering the color of human skin in the long span of human evolution, Jablonski and Chaplin note that there is no empirical evidence to suggest that the human ancestors six million years ago had a skin color different from the skin color of today's chimpanzees--namely pale-skinned under black hair. But as humans evolved to lose their body hair a parallel evolution permitted human populations to turn their base skin color dark or white over a period of less than a thousand years to adjust to the competing demands of 1) increasing eumelanin to protect from UV that was too intense and 2) reducing eumelanin so that enough UV would penetrate to synthesize enough vitamin D. By this explanation, in the time that humans lived only in Africa, humans had dark skin to the extent that they lived for extended periods of time where the sunlight is intense. As some humans migrated north, over time they developed white skin, though they retained within the gene pool the capability to develop black skin when they migrated to areas with intense sunlight again, such as across the Bering Strait and south to the Equator. [1] "
"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. =]"
I know someone with a son who has Asperger's. He would violently disagree with your assessment of it improving longevity and survival.
Are you sure that's a beneficial mutation?
This from the article:
"The boy is healthy now, but doctors worry he could eventually suffer heart or other health problems."
Doesn't sound like it's necessarily beneficial.
Interesting question. For a mutation to be beneficial, its positives have to outweigh its negatives, over the long run. Throughout most of human history (to a lesser extent today) being stronger and more robust was an advantage for a human. I don't think that advantage is outweighed by potential problems long-term.
Good point. I was actually trying to, for the sake of argument, concede that interbreeding caused skin color variations, but that this was irrelevant to whether or not allele frequencies had changed.
It takes a lot of calories (and protein) to maintain lean muscle. The hunter-gatherer lifestyle that shaped much of our evolution has these, but not in a reliable continuous stream. It's more of a boom-bust feast-famine thing.
We store fat for fuel reserves in good times, but in bad times we not only dip into the fat but into the muscle. Some details of mechanism make that necessary, mostly the way we run out of carnitine in the mitochondria during prolonged exercise. You can burn fat for a while in prolonged exercise or starvation, then you have to cannibalize some protein to replenish carnitine to allow your mitochondria to process fat.
That turns out not to be a bad idea, since burning some muscle gives you less mitchondrial mouths to feed in the first place and saves some fat for later. That's the adaptation most of us have.
It's hard to say how the kid's super-muscle mutation would have worked out had it surfaced back in the last Ice Age. The kid might have lorded it over his skinny pack mates, or he might never have made it.
I agree that micro-evolution is one paradigm that fits the observed conditions. Is it the only possible one?
I will grant you that it seems an adequate answer, and inasmuch as I'm qualified to judge such things, it's probably correct. However, I should observe that regional variation in melanin content in human skin is a far cry from speciation. Making the leap from micro-evolution to macro-evolution isn't supported by observation.
That doesn't mean it's wrong, mind you; it just means that it isn't proven.
I don't concede anything until the opponent shows she understands science to some minimal level. Elsie spouts creationist propaganda and ridicules known science.
It is only worth debating if one has an opponent.
"I should observe that regional variation in melanin content in human skin is a far cry from speciation. Making the leap from micro-evolution to macro-evolution isn't supported by observation."
There is only evolution. Micro and macro are scientific techincal uses you would not understand. Scam artists at AIG and ICR have twisted the definition of micro and macro to deceive you into thinking they are different processes.
I read your post where you admitted that the find "does complicate things". I briefly fainted, but have revieved now. It is unfortunated that I have to leave for Little Rock within the hour. A "civil" discusion of the latest crevo news with my favorite crumudegoen is long overdue.
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