"These monsoon rains strengthened the Nile's flow, forming a northbound 'highway,'" Vaks said.
"The climate along the shoreline of the Red Sea was also much less extreme during this period, and archaeologists have found evidence of migration along the coasts."
(See a map of ancient human migration.)
"It is reasonable that there is a connection between a wet period along the Sinai-Negev land bridge and the appearance of early modern man for the first time outside of Africa," he added.
Experts have been examining the influence of climate on human migration and evolution for years. But this is the first time researchers have turned up hard evidence, Vaks' team said.
(Read related story: "Climate Change May Have Helped Humans Out of Africa, Study Says" [June 12, 2006].)
"This is the first time there is both evidence and exact dating," said Hebrew University geographer and research team member Amos Frumkin.
"This evidence fits within a network of other information we have on the migration of modern humans from Africa to Asia."
Emory University anthropologist John Kingston, who was not involved in the study, agreed that the new find provides important physical clues to the history of early human migration.
"This is really significant in providing empirical evidence for ideas that existed already," he said. "To have empirical evidence like this is golden."
The connection between the rainy spells seen in the cave formations and the existing archaeological evidence in Carmel and Nazareth is also reasonable, Kingston added.
The use of speleothems to map climates is increasingly popular, he continued.
"What speleothems have that nothing else has is resolution," Kingston said.
"It's really a good terrestrial indicator. You can not only get the environmental information but link it to dates as well, and that's the key part here."
The research team also included Hebrew University's Alan Matthews and GSI's Ludwik Halicz. Their findings are published in the current issue of the journal Geology.
The comfortable corridor through the Sinai and Negev wilderness didn't last long, said GSI's Miryam Bar-Matthews, who took part in the research.
"Anton [Vaks'] work showed that those who moved northward from Africa could not return. Immediately afterward, the desert once again became a real harsh desert, so they couldn't move back," Bar-Matthews said.
Kingston agreed but added this was likely not the only period of comfortable passage through the northern Sahara.
"I would advocate that these corridors come and go," he said. "It's not like this was the last chance to get out of Africa or back in."
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