A fossil tour doesn't have to mean an aging rock band's reunion concerts. The State Department gave final approval Wednesday for one of the world's most famous fossils — the 3.2 million-year-old Lucy skeleton unearthed in Ethiopia in 1974 — to tour the U.S. on exhibit for the first time.

The Smithsonian has objected to the idea, however, because museum experts don't think the fragile remains should travel. So Lucy won't be stopping at the National Museum of Natural History, but in other U.S. museums instead.

Smithsonian scientists feel that certain artifacts, such as Lucy, are too valuable for the stresses of travel and should remain in their homes, according to National Natural History Museum spokesman Randall Kremer.

"This is one of the most important specimens relating to human origins in the world," Kremer said Wednesday. "We think it is too much of a risk to have it travel for the purposes of public viewing."

Even in Ethiopia the public has only seen the real Lucy remains twice. The Lucy exhibition at the Ethiopian Natural History Museum in the nation's capital, Addis Ababa, is a replica and the real remains are usually locked in a vault.

"We share with them the fact that artifacts like this need to be surrounded with the utmost care, but that should not preclude them from traveling," said Dirk Van Tuerenhout, curator of anthropology at the Houston Museum of Natural Science, which is arranging the tour. He added that representatives from his museum did deem some of the other artifacts offered by the Ethiopian government unable to travel.

"If you are able to showcase an original fossil, then you have a story, then you have a point of attraction that will bring in the most number of people, and then you can tell them that story," Van Tuerenhout said.

The State Department approved the exhibit for temporary importation into the U.S., saying that display of Lucy and the other artifacts is in the national interest because of their "cultural significance." The official announcement was published Wednesday in the Federal Register.

Lucy goes on display at the Houston Museum of Natural Science on Aug. 31, continuing through April 20, 2008. The other tour stops have not been finalized, according to museum spokeswoman Melodie Francis. But in announcing the plans to display the artifact last October, Ethiopian officials listed Washington, New York, Denver and Chicago as tour stops.

The fossilized remains were discovered in 1974 in the remote, desert-like Afar region in northeastern Ethiopia. Lucy is classified as an Australopithecus afarensis, which lived in Africa between about 4 million and 3 million years ago, and is the earliest known hominid.

Most scientists believe afarensis stood upright and walked on two feet, but they argue about whether it had ape-like agility in trees. The loss of that ability would suggest crossing a threshold toward a more human existence.