As humans we take many things for granted. One is surely the ability to walk, crawl, or even, after a little too much to drink, drag ourselves over to a lovely member of the opposite sex. Plants have no such luxury. For much of the long history of green life on land, plants had to be near each other, touching almost, to mate. Moss lets its pale sperm into rainwater to float to nearby partners, as did other early plants, but this method requires moisture. Vegetation could only survive in those damp corners where beads of water connected, dependably, a male to a female. Most of the Earth was brown.
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.