How ancient whales lost their legs, got sleek and conquered the oceans

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.

<< You believe those because you believe Scientists and the institution of Science over the Bible. >>

I tentatively believe what is strongly supported by actual evidence.

<< I know the Bible is true because the Holy Spirit has given me that "burning in the bosom" as you say. I hope that clears it up for you a little. >>

Doesn't clear up a thing. That is exactly what *I* said.

Let's test my claim -- and yours. Here is a question for you? If I were to demonstrate for you that your understanding of evolution is false, what would you do? I am not saying I can -- or that I wil even try. All I am asking is: If I were to do so, what would you do?

I have a very strong "feeling" about what your answer will be -- but my "feeling" is not evidence. Only your answer is evidence -- if you are honest in that answer. I always give others the benefit of the doubt till I get a good sense of their track record -- so I am assuming you will answer honestly.

'may' = speculation

I find it curious that creationists continue to single out evolution as being speculative, even after it is repeatedly explained that all of science is speculative, and evolution is no more speculative than any other scientific field of study. It is as though they are not interested in honesty, but rather they seek to create confusion amongst those without a background in scientific education.

I think the argument is that some creatures accidentally lost their hind legs and that this proved to be advantageous, but it was not necessary for this to happen, because creatures like the ancestors of the wahles, like walruses, survived qiite nicely. However, Darwinism always had had some teleology built into it, a least the explanations of it, because it is always a backward look. It has the same logical problems as historicism.
.

There is NOTHING in the Bible which either supports or condemns evolution. Nothing. NADA.

Only in the fertile brains of determined fanatics with an Ayatollahesque view of scripture could anything be gleaned from it that does.

You are like those who can not see the forest for the trees. You become wrapped up in segments of extracted verse and miss the big picture.

You would have made GREAT Pharisees.

The Message in the Bible is a simple one - God created the world and everything in it, man sinned, God sent His Son to redeem us and through His suffering and death we are saved should we accept His words, believe in Him and keep God's commandments. Christ never commanded that we not believe in evolution, nor is such a commandment in Mosaic Law.

Get over it. Evolution happened. Its a scientific fact. Unless you want to join the Inquisition and the Medieval Papacy and condemn a sun-centered world because some passage in the Old Testament states that God made the sun stand still in the sky. You are just making yourself look foolish, the Bible look foolish and bringing disdain and criticism on Christ and the Bible itself. And it isn't necessary.

The reality and sacrifice of Christ doesn't stand on the ability to disprove evolution.

The medieval papacy said nothing bout a geocentric universe, nothing that is, that medieval phisliphers said. Ptolomy was the reighing authority, and his thories fit the observable data very well, better than the theory of Copernicus. It wasn't until the studies of Kepler that a Copernican model that fit the data because plausible. It wsn't until Newton that a better celestial mechanics was available. Galileo was right but his theory had holes in it.

Ok, please forgive my sarcasm. It's just that I've seen these debates get all tangled up in the Evos defining the terms and claiming victory.

I admit that I have a bad habit of believing people will try to understand what I mean, but in these threads, most would rather split hairs on definitions.

This is what I mean by unproven theories....The theory that a whale underwent multiple mutations, some adding positive addaptations, is not proven. Science has proven mutations removing information. It's the theory that mutations could add information that is unproven. You can call my wording redundant, but you can't say that the tale of whale wondering is proven.

"I have no children. Nonetheless, if I did, such a statement would not amount to an argument against any scientific theory."

Maybe it's not an argument, but it is an attempt to demonstrate that there are other evidences which convince stronger then a whale tale.

I do have children. I was part of their creation. It was the most eye opening event in my life. I can't explain it in words, but it convinced me of a "Supreme Designer" if you will, and not random accidents.

You can attack that with all the science in the world, but it all evaporates when I look in the eyes of my children.

Have a good night.

Sincerely

"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.

They also claim that the apes are our "forefathers"!!!
How come then that the apes are still around???

<< They also claim that the apes are our "forefathers"!!!
How come then that the apes are still around??? >>

The "apes" that were our "forefathers" are not still around.
They were the "forefather" of all modern apes, including humans.

Oh -- I forgot the !!! There -- that makes my argument so much more persuasive!!!

..It's the theory that mutations could add information that is unproven...

Huh? It's not a theory, it's an observed fact.

Consider the classical case of sickle-cell. There is a single point mutation that causes the body to produce hemoglobin-S rather than normal hemoglobin.

If you are homozygous for hemoglobin-S, you have sickle-cell anemia.

If you are heterozygous for it, you have no symptoms at all, but are resistant to malaria.

A heterozygote does in fact have more information in his genome: enough to produce two kinds of hemoglobin rather than just one.

This is what I mean by unproven theories....The theory that a whale underwent multiple mutations, some adding positive addaptations, is not proven.

As I have said, this is a trivially true statement. The theory that explains how gravity operates is also not proven. All theories in science are not proven, nor will any theory in science ever be proven.

Science has proven mutations removing information. It's the theory that mutations could add information that is unproven.

Actually, mutations tend to shuffle around information. Whether or not that information is "meaningful" depends on the specifics of the shuffling. Whether or not such meaningful information proliferates is dependent upon environmental conditions.

Maybe it's not an argument, but it is an attempt to demonstrate that there are other evidences which convince stronger then a whale tale.

Your statement did not amount to any evidence.

I do have children. I was part of their creation. It was the most eye opening event in my life. I can't explain it in words, but it convinced me of a "Supreme Designer" if you will, and not random accidents.

Your reaction is an emotional response, and not a logical explanation. That you may "feel" that a "Supreme Designer" exists as a result of your children is not actual evidence to the fact, nor has it any bearing on the validity of the theory of evolution.

You can attack that with all the science in the world, but it all evaporates when I look in the eyes of my children.

It would appear, then, that you are selectively ignoring reality without a rational basis.

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.<

Hint: God doesn't like people who deny his wonders (Evolution being one of them).

Aw if you saying Evolution is a God created wonders your in effect agreeing with the top statement ...that the first thing that happen is an Intelligent God Design the Evolution mechanism...I have no particular problem with that but Creation by Intelligent Design is not Creation by Evolution

Because what you suggest is Evolution is God created hardware just running a God created program

"There is NOTHING in the Bible which either supports or condemns evolution. Nothing. NADA."

Huh? The Scriptures tell us there was no death before the sin of Adam. God created man in his imagine, you think He might look like an ape or a single cell slime? Evolution implies you gotta die and evolve, die and evolve, die and evolve, die and evolve...

"Your statement did not amount to any evidence."

Not evidence for you, but evidence to me. I understand, because you don't have children. It's just my way of trying to show you that all of your "high falooten" knowledge is not the only thing that convinces people.

"Your reaction is an emotional response, and not a logical explanation. That you may "feel" that a "Supreme Designer" exists as a result of your children is not actual evidence to the fact, nor has it any bearing on the validity of the theory of evolution."

Of course it's emotional. And the Evos posting their beliefs aren't emotional? Here again, it's not evidence to you, but it certainly has bearing on the validity I place on the theory of evolutionary origins.

"It would appear, then, that you are selectively ignoring reality without a rational basis."

It would appear that YOU are ignoring the reality that children bring into my thinking without a rational basis.

Good night.

Sincerely

"They also claim that the apes are our "forefathers"!!!"

Well, they have to believe that we're decended from rocks and rain. You see, before there were the apes, you had to be a flipper relative and then a goo ball. And the goo balls and other nasty slime was a result of rain and the cooling off of rocks. You see, the rocks were real hot because they were a result of an explosion in space that came from nothing.

Hey, I believe it! I also believe that Keebler really has elfs making cookies in trees. I've seen the commercials, so it's gotta be true!

Not evidence for you, but evidence to me.

Then your evidence is purely subjective, and is of no use.

I understand, because you don't have children.

There are many who do have children who have not come to the same conclusion as you. Clearly the state of "having children" does not amount to evidence against the theory of evolution.

It's just my way of trying to show you that all of your "high falooten" knowledge is not the only thing that convinces people.

There is no need to make this point. I am aware that many individuals choose to ignore knowledge when they do not wish to be convinced of facts that they do not wish to believe, instead relying upon emotion as a means of escaping reality.

Of course it's emotional. And the Evos posting their beliefs aren't emotional?

Some are. Some are not. However, the emotion behind a claim is not evidence for a claim. No matter how "emotionally" you feel about a subject, your emotion is not evidence for the nature of reality.

Here again, it's not evidence to you, but it certainly has bearing on the validity I place on the theory of evolutionary origins.

Then you acknowledge that your rejection of the theory of evolution is not based upon logical reasoning, but in fact upon logical fallacies.

It would appear that YOU are ignoring the reality that children bring into my thinking without a rational basis.

I am not ignoring what you have introduced into the discussion. I am pointing out the fact that your children, and how you think of them, does not in any way demonstrate that the theory of evolution is invalid.

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