Jet streams
occur at very high altitudes — 30,000 to 40,000 feet — which is why they were not definitively identified until World War II, when pilots noticed intense headwinds during
long -
distance military missions.
Until recently, most biologists thought that
long -
distance pollination
occurred only rarely, with fewer than one plant in a hundred having parents separated by more than 100 metres, says Norman Ellstrand, a plant population geneticist
at the University of California
at Riverside.