Posted on 05/31/2005 12:03:06 PM PDT by PatrickHenry
In a stunning example of evolution at work, scientists have now found that changes in a single gene can produce major changes in the skeletal armor of fish living in the wild.
The surprising results, announced in the March 25, 2005, issue of journal Science, bring new data to long-standing debates about how evolution occurs in natural habitats.
“Our motivation is to try to understand how new animal types evolve in nature,” said molecular geneticist David M. Kingsley, a Howard Hughes Medical Institute investigator at the Stanford University School of Medicine. “People have been interested in whether a few genes are involved, or whether changes in many different genes are required to produce major changes in wild populations.”
The answer, based on new research, is that evolution can occur quickly, with just a few genes changing slightly, allowing newcomers to adapt and populate new and different environments.
In collaboration with zoologist Dolph Schluter, at the University of British Columbia, Vancouver, Canada, and Rick Myers and colleagues at Stanford, Kingsley and graduate student Pamela F. Colosimo focused on a well-studied little fish called the stickleback. The fish — with three bony spines poking up from their backs — live both in the seas and in coastal fresh water habitats all around the northern hemisphere.
Sticklebacks are enormously varied, so much so that in the 19th century naturalists had counted about 50 different species. But since then, biologists have realized most populations are recent descendants of marine sticklebacks. Marine fish colonized new freshwater lakes and streams when the last ice age ended 10,000 to 15,000 years ago. Then they evolved along separate paths, each adapting to the unique environments created by large scale climate change.
“There are really dramatic morphological and physiological adaptations” to the new environments, Kingsley said.
For example, “sticklebacks vary in size and color, reproductive behavior, in skeletal morphology, in jaws and teeth, in the ability to tolerate salt and different temperatures at different latitudes,” he said.
Kingsley, Schluter and their co-workers picked one trait — the fish's armor plating — on which to focus intense research, using the armor as a marker to see how evolution occurred. Sticklebacks that still live in the oceans are virtually covered, from head to tail, with bony plates that offer protection. In contrast, some freshwater sticklebacks have evolved to have almost no body armor.
“It's rather like a military decision, to be either heavily armored and slow, or to be lightly armored and fast,” Kingsley said. “Now, in countless lakes and streams around the world these low-armored types have evolved over and over again. It's one of the oldest and most characteristic differences between stickleback forms. It's a dramatic change: a row of 35 armor plates turning into a small handful of plates - or even no plates at all.”
Using genetic crosses between armored and unarmored fish from wild populations, the research team found that one gene is what makes the difference.
“Now, for the first time, we've been able to identify the actual gene that is controlling this trait,” the armor-plating on the stickleback, Kingsley said
The gene they identified is called Eda, originally named after a human genetic disorder associated with the ectodysplasin pathway, an important part of the embryonic development process. The human disorder, one of the earliest ones studied, is called ectodermal dysplasia.
“It's a famous old syndrome,” Kingsley said. “Charles Darwin talked about it. It's a simple Mendelian trait that controls formation of hair, teeth and sweat glands. Darwin talked about `the toothless men of Sind,' a pedigree (in India) that was striking because many of the men were missing their hair, had very few teeth, and couldn't sweat in hot weather. It's a very unusual constellation of symptoms, and is passed as a unit through families.”
Research had already shown that the Eda gene makes a protein, a signaling molecule called ectodermal dysplasin. This molecule is expressed in ectodermal tissue during development and instructs certain cells to form teeth, hair and sweat glands. It also seems to control the shape of - bones in the forehead and nose.
Now, Kingsley said, “it turns out that armor plate patterns in the fish are controlled by the same gene that creates this clinical disease in humans. And this finding is related to the old argument whether Nature can use the same genes and create other traits in other animals.”
Ordinarily, “you wouldn't look at that gene and say it's an obvious candidate for dramatically changing skeletal structures in wild animals that end up completely viable and healthy,' he said. "Eda gene mutations cause a disease in humans, but not in the fish. So this is the first time mutations have been found in this gene that are not associated with a clinical syndrome. Instead, they cause evolution of a new phenotype in natural populations.”
The research with the wild fish also shows that the same gene is used whenever the low armor trait evolves. “We used sequencing studies to compare the molecular basis of this trait across the northern hemisphere,” said Kingsley. “It doesn't matter where we look, on the Pacific coast, the East coast, in Iceland, everywhere. When these fish evolve this low-armored state they are using the same genetic mechanism. It's happening over and over again. It makes them more fit in all these different locations.”
Because this trait evolves so rapidly after ocean fish colonize new environments, he added, “we wondered whether the genetic variant (the mutant gene) that controls this trait might still exist in the ocean fish. So we collected large numbers of ocean fish with complete armor, and we found a very low level of this genetic variant in the marine population.”
So, he said, “the marine fish actually carry the genes for this alternative state, but at such a low level it is never seen;” all the ocean fish remain well-armored. “But they do have this silent gene that allows this alternative form to emerge if the fish colonize a new freshwater location.”
Also, comparing what happens to the ectodysplasin signaling molecule when its gene is mutated in humans, and in fish, shows a major difference. The human protein suffers "a huge amount of molecular lesions, including deletions, mutations, many types of lesions that would inactivate the protein," Kingsley said.
But in contrast, “in the fish we don't see any mutations that would clearly destroy the protein.” There are some very minor changes in many populations, but these changes do not affect key parts of the molecule. In addition, one population in Japan used the same gene to evolve low armor, but has no changes at all in the protein coding region. Instead, Kingsley said, “the mutations that we have found are, we think, in the (gene's) control regions, which turns the gene on and off on cue.” So it seems that evolution of the fish is based on how the Eda gene is used; how, when and where it is activated during embryonic growth.
Also, to be sure they're working with the correct gene, the research team used genetic engineering techniques to insert the armor-controlling gene into fish “that are normally missing their armor plates. And that puts the plates back on the sides of the fish,” Kingsley said.
“So, this is one of the first cases in vertebrates where it's been possible to track down the genetic mechanism that controls a dramatic change in skeletal pattern, a change that occurs naturally in the wild,” he noted.
“And it turns out that the mechanisms are surprisingly simple. Instead of killing the protein (with mutations), you merely adjust the way it is normally regulated. That allows you to make a major change in a particular body region - and produces a new type of body armor without otherwise harming the fish.”
I should have been more precise: members of the order carnivora.
Are all members of the order carnivora of the same "kind"
YEC INTREP
Why should we take the superstitionists seriously when historical fact is something they consider "silly?"
> Perhaps the creator is tweaking the code behind the scenes for all you know.
That is a possibility. The more Christians who come to realize that God used evolution, rather than just snapping his fingers, the better off the Right will be.
> Your example of transition is that Pakicetus evolved into Ambulocetus, which evolved into Rodhocetus, which evolved into Procetus?
With the possibility of numerous steps in between each stage, that's certainly what the evidence suggests.
I'm just making sure the lurker and even you are exposed to material you show no sign of grasping. Crocs and alligators: 200 million years. Age of the Earth, 4.5 billion. There is no conflict between post 178 and post 53.
And just who "may-have" been the living ancestors of the single-celled guys? sans flagella by the way.
One idea is RNA World, where some large-sized pond, lake, tidal pool, whatever, has most of the functions of a single organism. There are other possibilities being researched, but there's already some evidence that the last common ancestor of all life is something older than any of the three main domains of cellular life known today. IOW, in RNA World, the whole soup is the organism. "Goo," I believe you prefer. Then cellular life forms at least twice as parasites on the Goo-organism: once as eubacteria and once as archaebacteria. Viruses may be the revenge of the Goo, naked or near-naked nucleic acid parasites on cellular life. Or viruses may be degenerate cellular life. At any rate, later on, eukaryotes form from a symbiotic relationship of certain eubacterial and archaebacterial cells.
Perhaps. Or He could have just snapped His fingers as He did with the Big Bang. Who knows? Evolutionists will eventually be humbled about their little theories one way or the other.
29+ Evidences for Macroevolution. If you're restricted to looking at short periods (say, a single human lifetime), then everything reproduces according to "kind." But there is unlimited "kind-creep" over longer periods of time. Why? Because there's no reason why not.
And what exactly are these "kinds?" Are a lion and a tiger the same "kind?" A horse and a donkey? A chimp and an orangutan? If the answer on the last one is "Yes," why is the chimp from all evidence more related to a human than it is to an orangutan?
In fact, we see every degree of relationship among extant animals. We see things that can't cross-breed at all, period. We see things with very low cross fertility. We see things with fair cross-fertility, but low fertility in the offspring.
We see examples of every stage of divergence. On a tree, you can see big branches with lots of little branches, medium size branches with some little branches, little branches with a few twigs, twigs that have barely grown apart, and every shade of gradation between the aforementioned. The tree of life is like that.
What it is NOT like is some number of obvious clusters (from-the-beginning distinct kinds; completely separate trees) which have had almost no time to sprout their own branches. The latter is a failed prediction of "Separate Kind" creationism, especially Young Earth creationism.
"Microevolution X 3.5 billion years = Macroevolution."
That's the same kind of hubris that kept alchemy alive for so long.
Theory = useful.
Superstition /= useful.
Then what does microevolution X 3.5 billion years equal? If it's happening small scale for billions of years, then doesn't that equal large scale over time?
Yes, it's a theory backed up by a great deal of evidence and over 100 years of scientific review.
Superstition= useful (to those same people)
But there is unlimited "kind-creep" over longer periods of time. Why? Because there's no reason why not.
Because you don’t know what conditions existed, (or what conditions are necessary), and can’t reproduce the event in the laboratory, and can’t show it to be statistically probable. All valid reasons as to why not. Why then are you so very sure that it happened at all?
Actually, none of those "problems" even address what would stop microevolution from becoming macroevolution over time. Those are just problems with making a straw-clutching you-can't-make-me-see-ist admit there's no limiting mechanism.
Yes, it's a theory backed up by a great deal of evidence and over 100 years of scientific review.
It's a theory backed up by the belief that a cloud of hydrogen will spontaneously invent extreme-ultraviolet lithography, perform Swan Lake, and write all the books in the British Museum.
P.S. Thanks Fred.
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