Separated at birth?
(Bonus points if you can identify the whale--the ship is a BIG hint)
Posted on 05/23/2006 4:08:38 AM PDT by PatrickHenry
When ancient whales finally parted company with the last remnants of their legs about 35 million years ago, a relatively sudden genetic event may have crowned an eons-long shrinking process.
An international group of scientists led by Hans Thewissen, Ph.D., a professor of anatomy at Northeastern Ohio Universities College of Medicine, has used developmental data from contemporary spotted dolphins and fossils of ancient whales to try to pinpoint the genetic changes that could have caused whales, dolphins and porpoises to lose their hind limbs.
More than 50 million years ago the ancestors of whales and dolphins were four-footed land animals, not unlike large dogs. They became the sleek swimmers we recognize today during the next 15 million years, losing their hind limbs in a dramatic example of evolutionary change.
"We can see from fossils that whales clearly lived on land - they actually share a common ancestor with hippos, camels and deer," said team member Martin Cohn, Ph.D., a developmental biologist and associate professor with the UF departments of zoology and anatomy and cell biology and a member of the UF Genetics Institute. "Their transition to an aquatic lifestyle occurred long before they eliminated their hind limbs. During the transition, their limbs became smaller, but they kept the same number and arrangement of hind limb bones as their terrestrial ancestors."
In findings to be published this week in the Proceedings of the National Academy of Sciences, scientists say the gradual shrinkage of the whales' hind limbs over 15 million years was the result of slowly accumulated genetic changes that influenced the size of the limbs and that these changes happened sometime late in development, during the fetal period.
However, the actual loss of the hind limb occurred much further along in the evolutionary process, when a drastic change occurred to inactivate a gene essential for limb development. This gene - called Sonic hedgehog - functions during the first quarter of gestation in the embryonic period of the animals' development, before the fetal period.
In all limbed vertebrates, Sonic hedgehog is required for normal limbs to develop beyond the knee and elbow joints. Because ancient whales' hind limbs remained perfectly formed all the way to the toes even as they became smaller suggests that Sonic hedgehog was still functioning to pattern the limb skeleton.
The new research shows that, near the end of 15 million years, with the hind limbs of ancient whales nonfunctional and all but gone, lack of Sonic hedgehog clearly comes into play. While the animals still may have developed embryonic hind limb buds, as happens in today's spotted dolphins, they didn't have the Sonic hedgehog required to grow a complete or even partial limb, although it is active elsewhere in the embryo.
The team also showed why Sonic hedgehog became inactive and all traces of hind limbs vanished at the end of this stage of whale evolution, said Cohn. A gene called Hand2, which normally functions as a switch to turn on Sonic hedgehog, was shown to be inactive in the hind limb buds of dolphins. Without it, limb development grinds to a halt.
"By integrating data from fossils with developmental data from embryonic dolphins, we were able to trace these genetic changes to the point in time when they happened," Thewissen said.
"Studies on swimming in mammals show that a sleek body is necessary for efficient swimming, because projecting organs such as rudimentary hind limbs cause a lot of drag, and slow a swimmer down," said Thewissen, who spends about a month every year in Pakistan and India collecting fossils that document the land-to-water transition of whales.
Researchers say the findings tend to support traditional evolutionary theory, a la Charles Darwin, that says minor changes over vast expanses of time add up to big changes. And while Sonic hedgehog's role in the evolution of hind limbs in ancient whales is becoming apparent, it is still not fully defined.
"It's clear when ancient whales lost all vestiges of the limb it was probably triggered by loss of Sonic hedgehog," said Clifford Tabin, Ph.D., a professor of genetics at Harvard Medical School who was not involved in the research. "But it's hard to say for certain because you're looking at events long after they occurred. As they suggest, there could have been a continual decrease in Sonic as the limbs reduced until the modern version of the animal arrived."
The study itself, combining fossil and developmental data, is notable, Tabin said.
"Whales went through this remarkable transformation to become more like the ancestral fish," Tabin said. "Convergence of evolutionary studies and developmental genetics give us another piece in this growing tapestry of how genetic changes lead to morphological change. It is a remarkable process that was achieved simply and led to profound consequences in how whales were able to survive. Only now in the last five years are we developing this understanding of how the world of evolution is controlled genetically."
###
In addition to UF and Northeastern Ohio Universities College of Medicine, scientists from the Natural History Museum of Los Angeles County and the Indian Institute of Technology were involved in the research. Financial support was provided by the National Science Foundation, the National Institutes of Health and the Indian Department of Science and Technology, New Delhi.
|
I'm sorry, but this can't possibly be true. Everyone knows that Haeckel guy was a fraud, so therefore embryology can never, ever, ever tell us anything at all about evolution. Or something.
LOL
"scientists say the gradual shrinkage of the whales' hind limbs over 15 million years was the result of slowly accumulated genetic changes that influenced the size of the limbs and that these changes happened sometime late in development, during the fetal period."
Then, the whales decided to make disingenuous films about guns at Columbine and leftist propaganda about 9/11.
A bunch of wristwatch parts tumbled in a clothes dryer for 35,000,000 years won't put themselves together into a wristwatch; not even if you run it for 100,000,000 years.
I don't believe it.
Now, I'm sure you know ABSOLUTLEY NOTHING about evolutionary theory - what it ACTUALLY is, how it works, the science behind it....or you wouldn't throw out the old stupid teleological argument.....which has been addressed hundreds of times.
No, you prefer to cling to your ignorance in hopes that it will buy you eternal salvation.
Hint: God doesn't like people who deny his wonders (Evolution being one of them).
I'm ALWAYS amazed when these folks think that MAN knows better than GOD. God set it up this way, all we have to do is live by the rules. Figuring out those rules is what science does. To deny obvious truths spread about you by the creator is blasphemous!
If certain genes turn off (or on) to effect some of these changes, isn't it reasonable to assume that there would be the occasional "throwback" that exhibited the properties of an earlier version?
Are they inferring that a creature's habits cause it to "evolve" to meet the preferred environment (whales lost their legs because they swam and legs were a hindrance) instead of having the changes occur, which would require the creature to either adapt or perish (whales lost their legs and had to become full-time swimmers because they couldn't get around on land)?
This evolution stuff gets so confusing sometimes - it seems that it can follow either the nature or nurture path and all findings are good because they give more credence to evolution even (or perhaps especially) if they seem to contradict the theory.
Must be a new creationist comic book being left at all the laundromats around the trailer parks. The old edition was "tornado in a junkyard." Now it's "wristwatch parts tumbled in a clothes dryer." Most impressive. It's good to see that the creationists are keeping up with the latest research.
"It's good to see that the creationists are keeping up with the latest research."
It's an excellent example of descent with modification.
I don't understand why, if whales evolved, we still have Sonic the Hedgehog today? < /luddite>
Depending on the mechanism of the gene regulation, it's possible. This is why humans are sometimes born with little tails.
Are they inferring that a creature's habits cause it to "evolve" to meet the preferred environment (whales lost their legs because they swam and legs were a hindrance) instead of having the changes occur, which would require the creature to either adapt or perish (whales lost their legs and had to become full-time swimmers because they couldn't get around on land)?
No, it is never accurate to say that a change occurred because the creature needed it. Evolution is not prescient. If a necessary beneficial mutation does not occur, the species simply goes extinct. The same mutation that caused these legs not to develop could happen in a land-dwelling whale ancestor as well. The difference is the land-dwelling ancestor can't manage without hind legs and would die, while the ocean-dwelling whale does better without its legs. By the time this change occurred, whales were already obligate marine creatures, with vestigial legs whose only utility is possibly as claspers (similar to sharks' claspers) for aid in mating. If the complete absence of hind legs is more beneficial, eventually that phenotype is likely to become the prominent phenotype.
It's more a question of, if you don't use your legs, does it matter if if you have a birth defect that causes them not to grow.
There are birth defects in humans where their limbs don't develop that's similar to what happened to the thalidomide babies in the '50's. If we were aquatic, we wouldn't need legs. And it would allow us to swim faster and easier, so it would likely be passed on to our offspring. No one would want to mate with the slowskys.
Yet you still have no alternate explanation.
I don't know if Sonic Hedgehog is a great name for a band, or an ice cream treat one would have with a SuperSONIC® Jalapeño Cheeseburger.
"tornado in a junkyard" was coined by Hoyle, and
Wickram(xxxx)...sorry I cannot remember how to spell
his name.
Both of them purported that they felt life was seeded
to earth from another extraterrestrial source, cuz of the "tornado in a junkyard making a 747" scenario
was unacceptable...Neither of them are creationists, they felt (from what I understood) that life had evolved on a different planet under different conditions than that found on earth.
Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.