Biogeography: where life lives

Next up—biogeography. Well, biogeography is the study of how animals, plants and other organisms have come to occupy the places on the globe that they do. Imagine a new island being born in the middle of the ocean. At first, it’s a hunk of rock. Lifeless. But gradually, seeds and insects and small animals, originating from nearby landmasses, get blown over on the winds. They come crashing ashore, pushed by the waves. Not all the organisms make it, but those that do, with time, adapt to island living, perhaps even evolving into new species. Just take birds. There are the finches of the Galápagos Islands, the birds of paradise of Papua New Guinea, the honeycreepers of Hawaii, and so on. In each case, a single island species diversified into an array of species found nowhere else on Earth. Biogeography’s also got something to say about why some closely related species flourish on different continents. It seems odd. Until you recall that Earth didn’t always look this way. A few hundred million years ago, all land was part of Pangaea—a hulking supercontinent. There were no vast oceans to interfere with the movements of organisms. But then, starting about 170 million years ago, the continents drifted like vast rafts across the sea. And the species living along the edges—they were split in two. Fast-forward to the present day, and you get a plant in South America whose close relatives grow in the tropical Pacific. We can use phylogenetic trees as sort of maps to help us reconstruct the movements of organisms across the planet.