Darwin’s Pony…and the Bulldog Who Loved Horses

Count The Toes on Our Petrified Pony

chi_7740Folks stop and stare at our fossil horse.  It is cute in a coltish way, all gangly and long-legged. And it is dynamic – rearing up as if it just saw you and whinnying a “Hello!” 

But sharp-eyed visitors take a second look. Our Merychippus demands a digital double-take. Count the toes. There’s one big hoof on each foot, as there should be. It’s a horse, of course. The French word is “solipede”, meaning “Single Toe Foot.”  Today, among all animals domestic and wild, horses and only horses have just the single, solitary toe to run on. 

Wait – look closely. There’s more. Our Merychippus has too many toes. There are extra digits, little ones, on the inside and outside of the main hoof.  The mini-toes have hoofs too but they’re narrow and pointed.

I imagine I’m petting our Merychippus along its muzzle, like I do to my neighborhood ponies. And I’d feel another odd thing – Merychippus has a more delicate, lightly-built face and nose. If you stare at the fossil, you see a row of molar teeth far smaller than any horse-owner would expect.

Those small molars and accessory digits tell a story that’s literally earth-shaking. Back in the 1870’s, Merychippus and the other three-toed horses shattered the scientific status quo. The side-toes made Archbishops fume and fuss and get red in the face. German philosophers smiled and puffed their pipes with satisfaction.

You see, Merychippus proved that Darwin was right.

Europe and Its Multi-Toed Equine Puzzles.

Down through the ages, since the time of the Babylonians, folks who could afford to own horses loved them.  Ditto for asses, mules and donkeys – all the solipedes were extraordinarily useful. Once they were domesticated, the equines offered farmers a powerful engine to pull a plow. Donkeys could carry produce to the market. Mules could turn the grinding stones. And war horses made the chariot the instrument of ancient Blitzkriege.

Since wealthy men had time to think about science, it was the horse-owning sector of society that pioneered the new discipline of Paleontology in the late 1700s and early 1800s.  Naturally, these men wondered how fossils could explain modern horse anatomy. Fossils were proving three great truths about the Earth: 1) It was very old. 2) It had gone through many ages, each with it own fauna and flora. 3) With each successive age, the animals got more and more modern.  Horses belonged to the most recent, most modern age. Horses with single hoofs were dug up only in rocks from the last slice of geological time, the Ice Age, when equines galloped around herds of giant mastodons and were chased by saber-tooth cats.

The mammoths and saber-tooths went extinct at the end of the Ice Age. Horses survived.

Anchitherium and Hipparion – Steps Up in Time?

hipparioncolor-copyIn the 1830s, some puzzling equine fossils were dug in older strata, European layers with more primitive cats and mastodons. The skeletons looked mostly equine…..but there was something wrong with the feet. Inside and outside were tiny extra toes.  This very first discovery of thee-toed horses received a name that would be famous: Hipparion.  The Hipparion-like horses were world-conquerors. They invaded Africa and Mongolia, China and India.

(We now know that our ancient human ancestors, Lucy and her Australopithecus relatives, thrived in African woodlands that had teeming herds of Hipparion.)

Further digging in France revealed a second horse-surprise. Long before Hipparion, there was a three-toed horse with extra digits that were far larger: Anchitherium. Radical scientists who defended the new idea of evolution seized upon the two fossil horses as evidence:

“SEE!  Fossils show that horses evolved!  First there was Anchitherium with big side toes….then after thousands of generations the toes got smaller, making a Hipparion, and finally the extra digits were GONE!  Voila! Modern horses had evolved!”

Evolution: A Theory Full of Horse-Holes!

horsesscott-copy

Many learned people thought it was bunk. “Too many holes in your story. There’s too much difference between Anchitherium and Hipparion!”  Skeptics were right. Anchitherium was way different from later horses. The face was short and the molar teeth were much too shallow top to bottom. And the molar crowns were simple.  Modern horses – and Hipparion – are renowned for their molars. The crowns are incredibly tall top to bottom and have crowns with complicated zig-zag patterns of enamel, an excellent design for chopping up tough grass.

Anchitherium had very low, very small molars that wouldn’t do at all for chewing grass. Anchitherium must have been forced to eat only soft fruit and succulent leaves. Dentally, it was NOT a horse.

Centennial USA – Darwin’s Bulldog.

Paleontological speculation about species evolution had begun in the 1820’s and ‘30’s, mostly in Paris. When Darwin published his “Origin of Species” in 1859, the topic boiled over – because Darwin offered a simple explanation for how evolution worked. Animals produced far too many offspring in every generation, so only those with superior genetic traits survived. That was “Natural Selection.”  The Establishment pooh-poohed and harrumphed and tried to stamp out Darwinian ideas. A brash young scientist, Thomas Henry Huxley, fought back. He knew anatomy and he knew fossils.

So eloquent was Huxley that he acquired the nickname: “Darwin’s Bulldog.” Of course Huxley used the European horse fossils as arguments…but still, those big gaps around Anchitherium were annoying.

Meanwhile, across the Atlantic, a new university was being built in Baltimore to revolutionary ideas: professors would do research in labs, graduate students would be given preference over undergrads and – Horrors! – WOMEN would be enrolled. 

This new institution was The Johns Hopkins University. Its official opening was set for the nation’s centennial, 1876. Bad news from Montana – the Sioux had wiped out General Custer – didn’t dampen the festivities. Johns Hopkins officials invited the best known biological scientist from Europe to give speeches – Thomas Henry Huxley.

Huxley advocated Darwinism in Baltimore. Then he took a fateful train ride north to New Haven, Connecticut. He visited the Yale museum where Professor Marsh supposedly had fossils from the American West that were close to European Anchithere-type horses.

Astonishing Riches in a Yalie’s Drawers.

Marsh opened up a museum drawer. There were hundreds of Anchither-style bones. Amazing. Another set of drawers had hundreds of Hipparion-like horses.  Doubly amazing.  Huxley was flabbergasted. “But…do you have missing links between Anchitheres and Hipparion? With a smile, Marsh had a whole room full of drawers opened up. Thousands of teeth, hundreds of skulls, dozens of full skeletons.

merychippuskin-copyYale drawers contained not one but a dozen missing links. There were tiny horses that must have been ancestors of Anchitherium. And tinier still ancestors of those ancestors.   The smallest, most primitive Yale ponies were no bigger than a poodle and had – count ‘em – four toes in the front paw.

Huxley made a suggestion. “When you dig the very first horses, the ones even earlier than these, why not call them the ‘Dawn Horse,’ Eohippus.”  Marsh did dig even earlier horses, and he did christen them Eohippus.

Marsh had already excavated links connecting Anchithere-style species with more primitive four-toed critters and with Hipparion-like species. His smallest three-toed link he called the “Middle Horse,” Mesohippus. Check out the Houston Mesohippus, mounted as if it were escaping the attack of a saber-tooth cat.

Most beautiful of all Marsh’s specimens were delicate skeletons the size of Shetland Ponies. The side toes were splendidly intermediate between Anchitheres and Hipparion. Bigger than in Hipparion, smaller than in the earliest Anchitheres.

But the teeth were better still. These horses had molars halfway between early species and the grass-eaters. The molar crowns were taller than in Anchitheres but lower than in Hipparion. Marsh had named this equine link “Merchippus.”

And to top it all off, the sediment layers in Nebraska and Wyoming just screamed: “Darwin is RIGHT!

The series of horses were buried in a series of layers, with the simplest molars and biggest side toes in the earliest levels.  Each American rock layer was like a frame in an old-fashioned movie, a slice of the Darwinian picture of change through millions of years.

Finally, Huxley knew why the European fossil horse story was full of gaps. “Horses evolved mostly in America… and only every once in a while species spread from here to the Old World!”

Dead right.

Merchippus and Modern Science.

Merychippus continues to tell its story in the 21st Century. A hundred times as many fossils have been dug.  Missing links are filled all the time – and gaps in the sequence of evidence are filled.  The horse family tree turned out to be a family blueberry bush, with many short branches going off sideways. 

The main theme of the equine saga is straight forward: Natural Selection was caused by climate change, as the old, warm, wet forests gave way to drier, cooler woodlands and plains. Horses had to evolve better teeth for tougher vegetation. And the feet had to change too.

Big side-toes were ideal for moving over soft, moist soil. But the shift to sun-baked plains demanded better shock-absorbing, and that meant a bigger central toes and smaller side toes. There were side branches too – some horse species specialized in the remaining patches of well-watered forests. Anchitherium was one of those forest-loving equines.

On the other hand, Merychippus was well on its way towards the new lifestyle. It was the direct ancestor of later, more advanced species, that led to Hipparion and then to all modern single-hoofed horses.

Salute to the Three-Toed Horse!

Take a moment to wave at our Merychipus. It was a fine, lively critter in its own time – one of the fastest hoofed animals and one of the best in eating the tougher leaves that were taking over the environment.

And give it a special tip of the cowboy hat for testifying to the central secret of Nature: Animals are NOT boring and static. Feet and molars are remolded by Nature to keep forests and plains full of creatures most wonderfully fit for their environment.

The gift that keeps on giving: Darwin and the Origin of Species

In conjunction with Darwin2009 Houston, a year-long celebration of Darwin’s 200th birthday and 150th anniversary of the publication of “On the Origin of Species,” HMNS will host a series of events exploring the contributions of this famous scientist.

Today’s guest blogger is Francisco J. Ayala, who shares some his findings here prior to his Feb. 24 lecture at the Museum, on “Darwin’s Gift to Science and Religion,” a part of HMNS’ Distinguished Lecture series.

The Origin of Species #1
Creative Commons License photo credit: gds

Darwin occupies an exalted place in the history of Western thought, deservedly receiving credit for the theory of evolution. In The Origin of Species, he laid out the evidence demonstrating the evolution of organisms.  However, Darwin accomplished something much more important than demonstrating evolution. Indeed, accumulating evidence for common descent with diversification may very well have been a subsidiary objective of Darwin’s masterpiece.  Darwin’s Origin of Species is, first and foremost, a sustained argument to solve the problem of how to account scientifically for the design of organisms. Darwin seeks to explain the design of organisms, their complexity, diversity, and marvelous contrivances as the result of natural processes. Darwin brings about the evidence for evolution because evolution is a necessary consequence of his theory of design.

The advances of physical science brought about by the Copernican Revolution had driven mankind’s conception of the universe to a split-personality state of affairs, which persisted well into the mid-nineteenth century.  Scientific explanations, derived from natural laws, dominated the world of nonliving matter, on the Earth as well as in the heavens.  Supernatural explanations, which depended on the unfathomable deeds of the Creator, were accepted as explanations of the origin and configuration of living creatures. Authors, such as William Paley in his Natural Theology of 1802, had developed the “argument from design,” the notion that the complex design of organisms could not have come about by chance, or by the mechanical laws of physics, chemistry, and astronomy, but was rather accomplished by an Omnipotent Deity, just as the complexity of a watch, designed to tell time, was accomplished by an intelligent watchmaker.

It was Darwin’s genius to resolve this conceptual schizophrenia.  Darwin completed the Copernican Revolution by drawing out for biology the notion of nature as a lawful system of matter in motion that human reason can explain without recourse to supernatural agencies. Darwin’s greatest accomplishment was to show that the complex organization and functionality of living beings can be explained as the result of a natural process—natural selection—without any need to resort to a Creator or other external agent.  The origin and adaptations of organisms in their profusion and wondrous variations were thus brought into the realm of science.

crab on the rocks
Creative Commons License photo credit: angela7dreams

Evolution can be seen as a two-step process. First, hereditary variation arises by mutation; second, selection occurs by which useful variations increase in frequency and those that are less useful or injurious are eliminated over the generations. “Useful” and “injurious” are terms used by Darwin in his definition of natural selection. The significant point is that individuals having useful variations “would have the best chance of surviving and procreating their kind.” As a consequence, useful variations increase in frequency over the generations, at the expense of those that are less useful or injurious.

Natural selection is much more than a “purifying” process, for it is able to generate novelty by increasing the probability of otherwise extremely improbable genetic combinations.  Natural selection in combination with mutation becomes, in this respect, a creative process.  Moreover, it is a process that has been occurring for many millions of years, in many different evolutionary lineages and a multitude of species, each consisting of a large number of individuals. Evolution by mutation and natural selection has produced the enormous diversity of the living world with its wondrous adaptations.

Francisco J. Ayala is a noted biologist and philosopher at the University of California at Irvine’s Department of Ecology and Evolutionary Biology. Don’t miss his lecture on Feb. 24 - or any of the other Darwin2009 events planned at HMNS this year.

Darwin2009: An “Aha!” moment worth celebrating

Archimedes
Archimedes: the original
“Aha!” moment.
 photo credit:
kimberlyfaye (away)

Behind many momentous scientific discoveries there seems to have been what we call an “aha moment.” Consider Sir Isaac Newton and the apple which is said to have hit him, causing Newton to hit on the notion of gravity. Consider Archimedes in his bathtub and his “Eureka” moment, which is just Greek for the German “Aha!”

Insights like these are different from those derived from problem solving. It seems that in this case, there is a sudden realization that we can explain something in a way we have never thought of before. In some cases the insight might have come almost immediately, in other cases it took years, if not decades for that lightning bolt to strike.

Consider Charles Darwin.

Charles Darwin
Creative Commons License photo credit:
CATR *Recomiendo ver
fotos con su tamaño original

Darwin was invited to be part of the second voyage of the HMS Beagle. It appears it was a last minute invitation (Here I could segue into what constitutes a ‘what if” moment, but I won’t.)  During his five-year long trip, Darwin spent most of his time on land, a good thing for a person prone to sickness, and a good thing for us too, as he was able to collect a lot of samples and make copious notes. This trip, which took him around the world, lasted from 27 December 1831 to 2 October 1836. Even though he was able to collect lots of data, it also appears that he was not until he was back home and reviewing his materials that the “aha!” moment came. When studying rare Galapagos mockingbirds, Darwin started considering the notion that that species changed over time. In other words, Darwin started to think of what we call “evolution.” (The mocking birds are currently part of an exhibit at the Natural History Museum in London.)

It was not until 1859 after further research and after much prodding from third parties, that Darwin finally published his famous tome “On the Origin of Species by Means of Natural Selection.”  It has been a bestseller ever since.

This year marks the 200th anniversary of Darwin’s birth and the 150th anniversary of the publication of his famous book. These two dates are celebrated across the world, although in the United States, Darwin will have to share birthday cake with a fellow called Lincoln, who happened to have the same birth day. In Houston, activities surrounding Darwin, his work and influence will be coordinated through the Houston Darwin 2009 organization.

A host of Houston-based institutions participate, including the Houston Museum of Natural Science. We have several events lined up, including a Darwin Day Festival on February 7 and a lecture series, starting in March 2009. Come help us celebrate one of history’s most famous Aha moments.