According to its curators, the exhibit seeks to demonstrate how people throughout history have tried to understand the mysteries of the natural world--however misguided their attempts often were. The exhibit certainly gives a sense of the creativity (and wackiness) of the human mind. As the online version of the exhibit describes, some of the creatures are the product of imagination, like the bunyip, a howling, man-eating monster of Australian legend. Others are clearly manmade deceptions, such as the Feejee mermaid (half fish, half monkey--wholly grotesque). The exhibit also includes real creatures thought to have inspired their mythic kin, such as a rendering of the huge extinct primate Gigantopithecus blacki, which lived in Southeast Asia and whose fossilized bones were likely the source for local legends about giants.

Understanding the unusual beliefs and scientific fallacies of earlier eras is important, of course. And AMNH is a good place to sponsor such an exploration. As with many other natural history museums founded in the 19th century, its dusty dioramas and collections--which in the 1870s featured a modest stuffed badger and dodo--have given way to vast troves of specimens pored over by fleets of excellent scientists and curators. It has also long been preoccupied by questions of what makes us human and why we believe what we do. The museum still boasts of the work done there by anthropologists Franz Boas and Margaret Mead and notes that it has been "a leader in forging new theories on the way we look at cultures."

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But as "Mythic Creatures" suggests, a museum that attempts to study human beliefs scientifically will soon find that many firmly held beliefs are not, in fact, scientific. Indeed, one need not travel to the homes of backward tribes on exotic Pacific isles to find such beliefs. Buried in the museum's archives are the artifacts of one of our own cultural myths: eugenics. The eugenics movement, which sought to improve the human race through better breeding and led to immigration restrictions and compulsory sterilization laws in the early-20th-century U.S., had a large and influential following. One of its most avid supporters was Henry Fairfield Osborn, the museum's president from 1908 until his retirement in 1933. A paleontologist by trade, he made the museum a hive of eugenics activity.

For decades the museum hosted international eugenics congresses and joint sessions of the Eugenics Research Association and the American Eugenics Society. Osborn and his friend Madison Grant, a museum trustee and an outspoken racist, were strong supporters of limiting immigration. Their efforts bore fruit with the passage of the 1924 Immigration Restriction Act, which placed quotas on immigrants from Southern and Eastern Europe because of their supposed racial defectiveness. One of the first things Osborn did after retiring as president of the museum was to take a busman's holiday in Nazi Germany. Osborn's nephew, Frederick Osborn, spent several years studying eugenics with his uncle at the museum and eventually took over leadership of the American Eugenics Society in the 1930s.

Most people are unaware of the museum's eugenic past; and officials there understandably are in no hurry to enlighten them. The American Museum of Natural History's Darwin exhibit last year played down Darwin's support for eugenics and neglected to mention its own role in the American eugenics movement. But the museum's embrace of eugenics was in keeping with its mission at the time. Its purpose, according to Osborn, was not merely educating the public about science, but encouraging the "propagation of socially desirable views."

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Has this mission changed? Mythic creatures are a far cry from eugenics, of course. And the museum has been scrupulous about eliminating incorrect displays--such as the one that, well into the mid-20th century, featured the developing races of man, with apes at the bottom and whites at the apex. The old-style "Hall of the Age of Man" has been reborn as the "Anne and Bernard Spitzer Hall of Human Origins," complete with spiffy new interactive models and lots of information about DNA.

But the museum still describes its purpose as more socially transformative than strictly educational. "In these exciting and challenging times," one description reads, "the museum will continue to seize extraordinary opportunities to transform our scientific vision into meaningful results, a strategy that has served the museum throughout its history." Well, not always.

In a culture where old-fashioned fantasy has been replaced by the television and video-game industries, and scientists create real human-animal chimeras for experimentation, perhaps there is something reassuring about exhibiting the quaint beliefs of previous eras. It reinforces the conviction that ours is a more sophisticated and scientifically literate age. It flatters our belief that the rational study of the natural world and its inhabitants will somehow inoculate us against the all-too-human urge to exploit nature and one another. But this is wishful thinking on par with a belief in unicorns. In the future, when curators at the American Museum of Natural History want to demonstrate the scientific missteps and misunderstandings of earlier generations, they need not mine the mythic past for material. The museum's own eugenic history is the Gigantopithecus in the room.

-- Ms. Rosen is a fellow at the Ethics and Public Policy Center in Washington.