Scientists continue to debate how humans arrived in America.
It remains one of the greatest mysteries of the past, said the narrator of "America's Stone Age Explorers," a "Nova" episode that aired Tuesday night on PBS.
There is a widely held belief that the first humans in America migrated from Siberia across the Bering land bridge into what is now Alaska.
An ancient spearhead found in Clovis, N.M., in 1933 provided researchers the first clue to human life, known as Clovis first.
Two of the biggest challengers to the Clovis-first theory are Bruce Bradley, an anthropologist from the University of Exeter, and Dennis Stanford of the Smithsonian Institute.
Bradley and Stanford revived an old hypothesis after discovering spearheads in a museum stockroom in France. The points were almost identical to Clovis points - leading to a theory suggesting Solutrean people from that region could have been the first humans in the Americas.
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UNM Professor of Anthropology Lawrence Straus, who was interviewed for the show, said the hypothesis has a few discrepancies.
"For one thing, the Solutrean and Clovis are separated by at least 5,000 years of time," Straus said. "Number two, the East Coast of the United States is separated from Spain and southern France, where the Solutrean culture was at the height of the last Ice Age, by the Atlantic Ocean."
The Solutreans civilization existed 18,000 years ago. Its artisans created elaborate cave art and carvings out of stone and wood. Straus said this cultural characteristic is proof the newly revived theory is impossible.
"There are no drawings of boats," he said. "These people had cave art, and they drew on portable objects as well. There is no representation of boats in that."
Stanford told "Nova" he wanted to see if people could travel that far in icy water, so he went to northern Alaska to consult with the indigenous Inupiat Eskimo tribe. They built canoes that have been in their culture for centuries and created a mock journey to Greenland.
"Archaeologists love that stuff," Straus said of Stanford's simulation, adding it doesn't provide proof.
He said Eskimos are the most recent arrivals to the Americas and have highly evolved marine strategies for boating and fishing.
"He (Stanford) portrays Solutreans as if they were Eskimos," Straus said. "How that is relevant to stuff that is 20,000 years old - that is the problem."
The British Broadcasting Corp. interviewed Straus for a program three years ago. He said it represented a narrow view of the debate, portraying Straus as a lone naysayer, while giving Stanford and Bradley ample time for their theory.
Straus said "Nova" did a better job of portraying a broader perspective, but he was on the program for seconds after spending hours for the interview.
"They don't give you enough time on camera to get important things across," he said.
Straus said spearheads shouldn't be the only piece of archeological evidence used to argue a hypothesis.
"Stone points are not people," he said.
