“In Africa, acacia trees evolved very long, sharp thorns—three inches or so—but that only provoked animals like giraffes and antelope to evolve long tongues to get past the thorns. Thorns alone didn’t work. So in the evolutionary arms race, the acacia trees next evolved toxicity. They started to produce large quantities of tannin in their leaves, which sets off a lethal metabolic reaction in the animals that eat them. Literally kills them. At the same time, the acacias also evolved a kind of chemical warning system among themselves. If an antelope begins to eat one tree in a grove, that tree
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