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NYCOM Professor Matthew Mihlbachler examines horse teeth.  (Source: Matthew Mihlbachler)

Prehistoric horses shifted from eating berries and fruit (like the pictured "Dawn Horse"), to leafy plants, then finally to grass as climate and vegetation changed.  (Source: Encyclopedia Britainnica)

Horses evolved in North America, but ironically all North American species perished at the end of the last ice age. The horses today are modern Eurasian descendants of ancient North American breeds.  (Source: University of Texas)

Modern horses have long teeth and complex cusps, well adapted for chewing high-silica grass.  (Source: Google Images)
Dietary changes take as much as a million years to broadly select a particular population, say researchers

Evolution says that the genetic material of the fittest species will typically survive and displace that of less fit species.  But there's much debate over finer details, such as how fast this process happens.  

Paleodental researchers at the New York College of Osteopathic Medicine have completed an important new study [press release] that examines how fast the process of evolution operates in response to changes in available diet.  The study looks at a relatively vast array of fossilized horse teeth and fossilized plant materials that date back as far as 55 million years ago.  

Their conclusion is that the old adage "you are what you eat" holds true -- if you give it about a million years.

NYCOM anatomy professor Matthew Mihlbachler [profile] said the key to the exciting study was in developing an effective method to tell what the horses were eating.  Past studies looked at the teeth on a microscopic scale or performed chemical tests to try to extract clues on the creatures' diet.  Such methods were laboriously slow.  

But Professor Mihlbachler used a new approach called mesowear.  This approach examines the shape of the tooth, particularly the sharpness of the cusps of molars.  The method is remarkably accurate as tooth shape is directly targeted to a specific animal's diet.

The result was a very comprehensive work.  Describes Professor Mihlbachler in an LiveScience, "We looked at wear patterns on horse teeth using mesowear through the entire history, from 55 million years ago in North America to the extinction at the end of the last ice age."

The horses of 55 million years ago would hardly be recognizable by today's standards.  No bigger than a modern fox, these petite creatures roamed warm, moist forests of North America munching on fruits and berries.  The creatures had four toes and their teeth were rounded to properly deal with their soft food.

Around 33 million years ago, the climate began to change and leafy shrubs suitable for the cooler weather displaced the fruity plants.  The process of evolution by natural selection transformed the horses into slightly larger leaf eaters.  The horses’ teeth became sharper in order deal with the new diet.

Describes Mr. Mihlbachler, "The signal we are getting in the change in horses' diet is very consistent with what we understand about how the climate was changing."

Horses underwent a final evolutionary metamorphosis approximately 18 million years ago as grasslands displaced the cool forests.  Grasses have high silica content, so horses had to develop longer teeth with more complex surfaces to deal with the new diet.  While leaf-eaters (with sharp teeth) persisted for several million years, they were eventually displaced entirely by the grass eaters.  In the mean time the grass eating horses' teeth continue to get longer with passing generations.

By 4 or 5 million years ago, the horses were completely adapted to grass lands.  And it paid off.  Horses expanded across most of North America and expanded across the Eurasian land mass.  There, early humans would encounter them and domesticate them, an encounter that would play a key role in human society.

Before that would happen in full, the pioneer North American breeds would die off, due to the last Ice Age abruptly ending, around 10,000 years ago.  But North America would yet again see horses, when the domesticated Eurasian descendants were reintroduced into the "New World".

The most intriguing thing about the study was not only that the dental record closely followed the change in foliage.  The more interesting thing was that it lagged slightly behind the changes, with the horses taking up to a million years to fully adjust to foliage changes.

This offers interesting evidence into the timescales of major evolutionary adaptation.  And it is relatively consistent with past evolutionary theory.  States Professor Mihlbachler, "The changes in the teeth are just slightly behind the environment and dietary trends, which is very consistent with the hypothesis of adaptation. Certainly, there were leaves and trees throughout all that time period, from 55 million years ago to the extinction. What we don’t know is why horses left those niches."

No scientist would claim that evolution happens the same way every time.  Thus it is important to practice caution when applying these time frames to other species or adaptive events.  But they do offer excellent evidence in support of key evolutionary hypotheses.  

Thomas Scandalis, dean of NYCOM concludes, "You are what you eat,’ we hear this all the time, but now we know it is true."

The paper on the work was published [abstract] in one of academia's most prestigious journals, Science.

If you're hungry for more evolutionary anatomical research, dig into NYCOM's February study [press release] [abstract] which examined a "bizarre" "pudgy" crocodile that lived in Madagascar, right before the mass extinction of the dinosaurs.  If you expected a vicious dinocroc like you might spot in a Sci-Fi channel movie special, you will be disappointed -- NYCOM Professor Robert Hill [profile] says the beast was a "gentle, vegetarian crocodile."

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RE: Science or stupidity?
By kingius on 3/9/2011 10:46:47 AM , Rating: 2
That's all well and good, but its also a strawman argument, in that it does not apply in every case but every opponent of evolution is painted with this brush to attempt to discredit them.

The stereo typical supporter of evolution believes that everybody who questions it is some kind of fundamental biblical literalist or at least attempts to paint anybody who questions evolution as being so, without access to the facts about the person they are speaking to. This is disingenuous and an attempt to shut down the debate before it can begin.

It also reeks of fear. It is time for science to be brave and tackle what is being said instead of side stepping it with irrelevant and inaccurate character assassination attempts against those perceived to be opponents.

That first specimen does not appear to be a horse at all, go look for yourself. I doubt that you are a christian literalist; if you come to the same conclusion as me, you will likely be labeled as one, or a moron.. because you /did not agree/ not because of any religious views.

RE: Science or stupidity?
By PaterPelligrino on 3/9/2011 1:14:14 PM , Rating: 3
I'm not quite sure where you're coming from - are you a creationist or not? I assume that you are. The link you provided in support of your argument points to a creationist site that claims that the horse - and by implication every species - was created in it's present form by Jehovah. This is from your link:

We may conclude, therefore, that there is no evidence that horses have ever been anything other than horses, and that these beautiful creatures, so useful to the human race, have not evolved, but were created by God, who long ago asked Job: 'Do you give the horse its strengths, or clothe his neck with a flowing main?'

Either you accept macro-evolution, but reject the above study on horses because you find it unconvincing; or you reject macro-evolution out of hand in all cases no matter what the evidence suggests. If the former, then yes we could debate the merits of this particular study. However, if you reject evolution in total, what is there to discuss? To be a creationist you must by definition reject macro-evolution. Evidence is irrelevant. The creationist's intellectual objectivity has been irredeemably compromised by uncritical subservience to the most anti-intellectual branch of Christian dogma.

When you guys claim to reject evolution because you find the theory unconvincing, one can't help but wonder if you think you are more intelligent than all the scientists and laymen who are convinced of evolution's validity - is it your opinion that superior intelligence determines adherence to the creationist camp? Or is what motivates evolution's proponents a vast anti-Jehovah conspiracy inspired by pride or Satan? Do you see yourselves as having been uniquely chosen by Yahwei to perceive the truth? Just how do you explain to yourselves all the people - including those other Christians sects - who do accept evolution?

The only people who reject macro-evolution are biblical literalists. First comes devotion to a literal reading of the Bible, then comes rejection of evolution. You'd do everyone a favor if, like Kurt Wise, you just came out and honestly admitted that evidence doesn't matter, you guys get your marching orders straight from Old Testament.

I take this line of argument because I have learned the hard way that no amount of evidence for evolution will ever make an impression on the creationist. He has far to great an emotional commitment to his faith to ever give the argument for species evolution a fair hearing.

RE: Science or stupidity?
By PaterPelligrino on 3/9/2011 8:47:13 PM , Rating: 4
btw, what really cracks me up about that creationist site you linked to is how they apply two entirely different standards of reasoning on the journey to their foregone conclusion.

Initially, they focus on the evidence, taking great pains to discredit the argument for the evolution of the horse from a smaller animal by pointing out discrepancies in the geological and anatomical evidence.

I don't want to offer a detailed rebuttal of that argument - frankly, I'm not qualified, and I'm not going to spend weeks familiarizing myself with the fossil record, hunting down references and reading primary sources. What interests me here is how after all that logical nitpicking about how the evidence does not support the evolutionary claims being made, the authors of your site go on to say, "We may conclude, therefore ... that these beautiful creatures, so useful to the human race, have not evolved, but were created by God."

Say what? Considering how much importance they claim to attach to logical rigor, where does that conclusion come from? It's like saying, "now that we've shown that the archeological and linguistic evidence does not support the thesis that the Chinese people are descendants of the ancient Egyptians, clearly they were transported to earth by space aliens."

Logic for the creationist is merely a tool to be used to discredit any threat to pre-existing, uncritical faith in the literal truth of the biblical narrative. Once they've dealt with that treat, logic goes right out the window and they feel free to "conclude" that Jehovah did it. You're no more likely to get a fair treatment of evolution from a creationist than you are to get an unbiased history of the Civil Rights Movement from the Grand Wizard of the local KKK chapter. You want an impartial opinion on possible threats to ground water from mining, you don't ask a lobbyist for the coal industry.

If creationists were as concerned with logic and evidence as they claim to be, and if the points they raise were valid, they would say that tho there is ample evidence for evolution in the fossil record, they remain unconvinced by the arguments linking the horse to that earlier animal - and stop at that. That they go on to say the only reasonable conclusion is that Jehovah created horses in their present form gives the game away. These people - and this is true of all creationist argument - are not interested in a fair examination of the evidence. So even without an exhaustive command off the underlying data, one can conclude that your creationists are playing fast and loose with the evidence.

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