A collection of more than 1,000 skulls at the University of Pennsylvania Museum is at the center of a debate about scientific objectivity. They were used 30 years ago to argue that the scientific method is vulnerable to cultural influence. Now they are being used to prove just the opposite.

Nineteenth-century scientist Samuel Morton collected and measured hundreds of human skulls at the University of Pennsylvania Museum. He compared the shape and size of skulls from people of different races, and out of those results determined intelligence is racially derived.

"His work is very strongly associated with race, especially in his stance, which was very pro-slavery," said Janet Monge, the curator of skeletons at the Penn Museum. "He was using his material in a ranking sense, what he considered to be most advanced versus most primitive."

Morton's conclusions are not valid. Science has shown since then that the size of a cranial cavity is not related to intelligence.

In his acclaimed 1981 book, "The Mismeasure of Man," Stephen J. Gould wrote not only were Samuel Morton's racist conclusions wrong, but the method he used to arrive at those conclusions was also wrong.

Morton packed empty skulls with as many peppercorns as they could hold, then shook them out and measured the contents. That way, he compared how much brain could be held by skulls of people of different races. Gould claimed Morton skewed his data by hard-packing the skulls of white people, and loose-packing those of black people.

But evolutionary biologist Jason Lewis repeated Morton's experiment at Penn in 2000, using hard plastic beads.

"Over 98 percent of the time, his measurements were very accurate," said Lewis. "We found 2 percent were off. In almost every one of those cases, the error was not in the direction of Morton's bias."

In his book, Gould used the case of Morton and his skulls to make a broader point about cultural bias in science, that scientists are unconsciously prejudiced.

The replicated experiment defends science as not culturally biased, even if its interpretation can be. It puts the Penn Museum in the tricky position of defending the accuracy of Samuel Morton's methods, while at the same time condemning his racist conclusions.