Wednesday, August 09, 2006

AMNH Darwin Exhibit: Going Back to the Glory Days When Horse Evolution Was Straight and Simple and Misleading

If you visit the American Museum of Natural History, you can see its permanent horse evolution exhibit (photo and text here), which shows the way scientists used to look at horse evolution, and also the more modern view. The museum's web site describes it this way:
The fossil horses aligned from right to left in the front of the display represent the evolution of horses as a steady progression along a single pathway -- until recently a widely held view of evolution. Here the horse is seen to evolve in a neat, predictable line, gradually getting larger, with fewer toes and longer teeth. Those arranged (also from right to left) in the back present a more current scientific view of evolution, determined through a method of analysis called cladistics, which has shown evolution to be a more complex, branching history, much like the genealogical history of your own family.

. . . Thus the display in the back shows that some later horses, such as Calippus, are actually smaller than earlier ones, and that other later horses, such as Neohipparion, still had three toes. This display is therefore both a classic demonstration of evolution and a paradigm of scientific method at the Museum.

What the display does not show you is that the old way of seeing horse evolution persisted for years in displays and textbooks, even after scientists knew it was misleading. One scientist called that "lamentable." George Gaylord Simpson put it this way:
The uniform, continuous transformation of Hyracotherium into Equus, so dear to the heart of generations of textbook writers, never happened in nature. Life of the Past, 1953.

Of course, the old way of presenting horse evolution as a straight line progression was far more effective in convincing the general public, and impressionable schoolchildren, than the "complex, branching history" display. Small wonder that the old way persisted for so long in exhibits and textbooks. I recall seeing such a display when I was younger, and it had a powerful impact on me. It was part of the reason that I originally thought that macroevolutionary theory was well supported by the evidence.

That said, we can all take heart that truth prevails, the museum has corrected its errors, and the current display is therefore "both a classic demonstration of evolution and a paradigm of scientific method at the Museum." Right?

Hold your horses! Take a walk on over to the Darwin exhibit and what do you find? Whoa! An exhibit of horse evolution that contains a straight line display of horsey hooves! (Photo and text here.) The progression couldn't be more linear and perfect. It shows a "neat, predictable line, gradually getting larger, with fewer toes." The display is described on the web site like this:
The evolution of the horse is well documented by a lengthy fossil record extending over 55 million years. During this time, episodes of relatively rapid modification were interspersed with long periods of little change. And it is clear that horses adapted to many different environments and pressures. Careful dating and analysis of fossils shows a clear succession of forms, from the dog-sized Hyracotherium to Equus, the modern horse.

Hyracotherium, Merychippus and Equus represent stages in the evolutionary path to living horses, a sequence that shows species becoming larger through time.

This raises the question: Why would they show a straight line display as the only visual paradigm, when scientists now know that such a presentation is inaccurate and misleading? Why would they not explain that the straight line display is the discredited way of understanding horse evolution? Could it be that the straight line presentation is such a powerful means of convincing the public (and impressionable schoolchildren), that they felt compelled to use it? Perhaps the ends justify the misleading means?

To be fair, the text goes on to explain that not all ancient horses evolved into larger forms, that members of some extinct groups were actually smaller than their ancestors, and that there are no universal trends in evolution. But how many museum goers read all the text accompanying displays? In my opinion, the overall impression one gets from viewing the display is that straight line progression is the best way to understand horse evolution, but that there are a few exceptions to this general pattern. This is at odds with the current scientific understanding, which the museum acknowledges in its permanent exhibit. The museum appears to have chosen a more persuasive display over a more truthful one.

If the permanent display is a "paradigm of the scientific method at the museum," then perhaps the Darwin display is a "paradigm of science as propaganda."

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Another post of mine related to the changing views on horse evolution is here.


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