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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 Surak on 3/5/2011 6:57:37 PM , Rating: 2
I call stupidity ... on Pjotr

The whole point of the story is that an animal changed it's diet, but it took a long time for teeth that were well adapted for the diet to arise through natural selection and evolution.

Cows changing to a diet of corn is in full agreement with this story. We've changed the diet of cows to corn, their teeth have not yet changed.

Oh and Pjotr, Corn is actually a type of grass. Dumbass.


RE: Science or stupidity?
By pwnsweet on 3/5/2011 7:38:17 PM , Rating: 1
quote:
We've changed the diet of cows to corn, their teeth have not yet changed.


...and they never will.


RE: Science or stupidity?
By AnnihilatorX on 3/5/2011 8:10:56 PM , Rating: 2
1 million years


RE: Science or stupidity?
By SebbesApa on 3/7/2011 8:11:58 AM , Rating: 2
Eh no.
"the fittest species will typically survive and displace that of less fit species." I suggest you read more on survival of the fittest and natural selection.


RE: Science or stupidity?
By GuinnessKMF on 3/7/2011 9:02:42 AM , Rating: 5
It's all about breeding, we've engineered an environment for cows where their evolution will have nothing to do with what people would consider a "fit" species, the gene pool that successfully mates the most. If uninterrupted the way things currently are, cows will evolve into the animals that produce the most delicious meat at the least feeding cost.

Given enough time they'll just be large sacks that produce beef marbled with bacon and cheese (you heard me, bacon from a cow).


RE: Science or stupidity?
By kingius on 3/8/2011 8:06:53 AM , Rating: 2
And that my friend, is a horrific example of the goal of some, unscrupulous people who want to get rich and by no means a normal end point.


RE: Science or stupidity?
By PrinceGaz on 3/5/2011 10:06:10 PM , Rating: 1
The cows which have teeth best suited to munching corn will be best suited to that diet, and either through natural selection (those cows which survive longer) or artificial selection (a farmer choosing them if that is a highly desirable trait), their teeth will most certainly change.

If it is artificial selection, it is quite possible for us to change a species almost to the point where it looks quite different from what was started with, in just a dozen or so generations. Take breeds of dogs for instance and what has been done with them in a couple of hundred years (usually to extremes which has damaged their health). A few hundred thousand years of natural selection would certainly change a cow's teeth to be best suited to what it is eating without our intervention.


RE: Science or stupidity?
By Pjotr on 3/7/2011 10:48:11 AM , Rating: 2
I think you missed the point totally. Start by watching the movie Food Inc.


RE: Science or stupidity?
By consumerwhore on 3/7/2011 2:29:09 PM , Rating: 2
You're talking about the movie that drills down the point of how cows are so grossly *misadapted* to the corn diet we have to feed them antibiotics from cradle to grave? (Among other ill side-effects...)

That "Food Inc." movie?


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