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The earth’s tropics teem¹ with species. They’re far more biologically diverse than the cooler parts of the planet. And scientists have credited higher temperatures and greater amounts of sunlight. But a new study claims that the secret to tropical biodiversity isn’t necessarily high temperatures—it’s the steadiness of those temperatures the whole year ‘round.

When today’s biodiversity was taking shape millions of years ago, seasons as we know them didn’t really exist. So temperatures all over the planet were much more consistent than they are today, even in regions where the temps were low.

Researchers looked at insect diversity today at the temperate² Harvard Forest in Massachusetts, in tropical Costa Rica and in the 53-million-year-old McAbee fossil bed in British Columbia. Which back then was steadily³ temperate. And ancient Canadian insect diversity was much more similar to modern Costa Rica’s than to the Harvard Forest’s. The work appears in the journal Paleobiology.

So we may have been thinking backwards—it’s not that the tropics have greater biodiversity. Could be that the seasons of today’s temperate zones have diminished the biodiversity that once flowered. And animaled.

Thanks for the minute for Scientific American’s 60-Second Science. I’m Steve Mirsky