Fifteen thousand ago, people from Siberia crossed what is a now-sunken land bridge to reach Alaska, becoming the first settlers in the Americas.
Some argue that people arrived here thousands of years earlier. But whenever they came, experts say, America's first residents probably couldn't have reached here without a piece of simple technology that's with us today.
The sewing needle.
Researchers who have examined ancient remains now say that without needle and thread to create warm clothing, the Arctic would have been uninhabitable and humans never would have made it to Siberia in the first place.
"It was a critical invention. It played a major role in our ability to adapt to really cold environments," said John Hoffecker, a researcher at the Institute of Arctic and Alpine Research at the University of Colorado at Boulder.
Hoffecker was among a group of U.S. and Russian researchers who discovered remnants of what might be the world's oldest known sewing needles at a Russian archaeological site. The 30,000-year-old needles, unearthed three years ago about 250 miles south of Moscow, are small, pointed ivory sticks with eyelets that must have been handcrafted.
"They had to be gouged out or drilled, which is obviously difficult work," Hoffecker said.
Scientists estimate that temperatures in that area 20,000 to 40,000 years ago - the end of the last Ice Age - were about 20 degrees Fahrenheit colder than present-day Moscow. But the needles, along with remains of foxes and hares trapped at the Kostenki archaeological site, show people had settled and were adapting to the area's frigid climate.
"You have to ask yourself, if they weren't sewing warm clothing, how else were they surviving?" Hoffecker said.
Opinion on the role of needle and thread is far from unanimous, however. Some argue that settlers could survive chilly winters for centuries by covering themselves with furs. The availability of food was a more important factor in where people settled, they say.
"Needles are important, but they're not the crucial element that led to the conquest of the north. The issue was the availability of food," said Olga Soffer, an anthropology professor at the University of Illinois Urbana-Champaign.
But proponents of the theory note that the sewing needle was a key development in many cultures. Although the earliest known needles have turned up in Russia, remnants of others believed to be at least 20,000 years old have been recovered all over Europe.
"They enhance survival and reproduction and they don't stay geographically isolated," said Richard G. Klein, a Stanford University anthropologist. "It's the absence of technology that was an impediment to living in the Arctic, not whether food was there. The food was always there."
Modern humans - or most of them, anyway - developed a need for clothing when they shed their body hair and migrated from Africa 60,000 to 100,000 years ago. The first clothes were likely made without needles: loose-fitting furs and pelts taken from animals killed for food, experts say.
The perishable nature of fur and fabric make it nearly impossible for archaeologists to determine when and where the first clothing was worn. Archaeological sites are rife with fossilized bones and dinner plates. But try finding a good pair of pants.
"Clothing degrades," said Soffer, who worked in the New York fashion industry as a promoter for 10 years before taking up anthropology in the 1980s. "We haven't found the equivalent of a Lucy," she added, referring to a famous set of human remains found in Ethiopia in 1974 that provided a key link between human and ape.
Soffer's examination of 90 clay fragments from the walls and floors of ancient huts in the Czech Republic revealed that people were wearing handmade clothes as far back as 29,000 years ago. She drew that conclusion from impressions of woven fabric imbedded in the clay from the homes of the Gravettian tribes that roamed from Russia to Spain between 22,000 and 29,000 years ago.
The impressions show a variety of fine weaving techniques, including open and closed twining and plain weaving - a type of weaving that would require a loom.
She and other researchers compared the woven patterns in the clay to the garb on "Venus" figurines, a group of about 100 statues carved all over Europe up to 27,000 years ago. The most famous is the Venus of Willendorf, housed at the Natural History Museum in Vienna, Austria.
Soffer says that what scientists originally mistook for intricate hairstyles on the statues were actually intricately woven caps, sashes and string skirts. That indicates people were creating fabrics thousands of years ago. "We're not saying it's what was actually worn, but we are saying it's what was depicted in their art," Soffer said.