In the U.S., the brilliant autumn foliage with its variations on red, orange, brown, and yellow never fails to delight the eye. In Israel and Europe, however, it’s mostly a one-color spread of yellow.

Researchers at the University of Haifa in Israel and the University of Kuopio in Finland have a new theory that stretches back 35 million years to solve the color riddle.

Their research, published in the journal New Phytologist, posits that during a series of ice ages and dry spells many tree species began an evolutionary process of producing red leaves to ward off insects.

In North America, north to south mountain chains enabled plant and animal “migration” with the advance and retreat of the ice, and the trees’ insect “enemies” migrated along with them.

In Europe and Israel, the mountains reach from east to west, so no protected areas were created. Many tree species did not survive the severe cold and the insects that depended on them for survival also perished.

At the end of the ice ages, most tree species that did survive in these areas had no need to cope with the insects because they were extinct, and therefore, over time, they no longer produced red leaves.

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