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Then one day more than 375 million years ago, it happened. One lineage of plants evolved pollen grains and seeds, and from then on nothing was the same. Let's not mince words. Pollen is plant sperm—two individuals per grain—surrounded by a single, often golden, wall that offers both protection and chariot. If the tension in the long story of plants was the distance between lovers, pollen was what would bring them together, over feet or even across continents. It was an evolutionary trick that transformed the world by letting strangers have sex.

Life remained a long shot. Pollen lunged into gusts of wind on the chance that a few grains would find their mark. With time came more contrivances. Pollen sacks burst, propelling the grains. Pollen evolved balloon-like wings to catch the breeze. Plants began to produce thousands, millions, billions of individual grains. They made many that one might succeed.

The target that each of those billions of pollen grains aims for is the naked ovule (the future seed) of another plant of the same species. At the ovule, which contains an egg cell, the pollen grain attempts to initiate a tube to connect sperm and egg. If the pollen lands on the wrong species of plant or is too weak or old, the tube does not form. But every so often it does, and then one of the two sperm, the chosen one, travels to fertilization, and a viable seed develops. That there are plants at all is testament to the more than occasional success of this intimate, improbable lottery.

Life proceeded like this, with pollen carried by wind and chance to ovules, for millions of years, until things changed again—"a soundless, violent explosion," the naturalist Loren Eiseley called it. In one lineage, individuals evolved seeds protected in fruits and surrounded by petals. That lineage, the angiosperms, did better because their ovules were protected (in ovaries, which turn into fruit), and because the petals attracted animals that, however accidentally, carried pollen on feathers, skin, or hair. Animals carried pollen from flower to flower more consistently than did wind, so plants with attractive petals were favored. Flowers evolved many colors to woo and nectar, an additional lure. Animals came in the thousands. Hummingbirds and honeycreepers evolved long beaks to reach nectar. Moths, bees, and flies evolved long, sucking mouthparts. Bats evolved long, sticky tongues—some of them nearly twice as long as their bodies.

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