The Next Species: The Future of Evolution in the Aftermath of Man by Michael Tennesen Read Free Book Online Page A

for tuskless males as well as females.
    Adapting to man is currently wildlife’s greatest evolutionary challenge. The animals in Ngorongoro Crater, including the human ones in the safari vehicles, are all descendants of our common ancestor Pikaia . Yet we are presently locked in mortal combat.
    The diversity of life is present in Africa’s game preserves, but one wonders how it began and how long it can continue.

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THE GROUND BELOW THE THEORIES
    M OST SCIENTISTS AGREE that the slow, lateral movement of the continents, their joining and separating on the surface of the planet, has strongly influenced the broad diversity of plants and animals that exist on earth today. During the Permian period all the continents joined together in one enormous landmass, a supercontinent, but after that extinction event, the supercontinent Pangaea began to split apart like a broken dinner plate with its pieces scattered across the oceans. This separation of the landmasses led to a corresponding separation of species of plants and animals. Newly separated species no longer exchanged genes with one another and over time isolated populations evolved away from each other and became separate species.
    The splendor of this evolutionary tale was on display when Darwin and the crew of HMS Beagle rowed up to the island of San Cristóbal, a black mound of volcanic rock in the middle of the Pacific Ocean, during their celebrated visit to the Galápagos Islands that began on September 17, 1835. At a distance the island looked desolate, but upon landing Darwin found it covered with plants that bore leaves, flowers, and seed-bearing fruits. He had been on a four-year expedition to South America and was now heading across thePacific on the long way back home to England. The crew of the boat hoped to catch a tortoise for some meat to make a tasty soup, but there were no tortoises on San Cristóbal.
    He did find numerous birds, which were unfazed by human presence as they looked for seeds in the bushes; they’d had no experience with humans. One of the crew even caught a bird with his hat. Darwin picked up an iguana and threw the animal into the water over and over, but each time it swam straight back to him. He yanked on the tail of another that was digging a burrow, and it turned and looked at him as if to say, “What made you pull my tail?”
    The Beagle docked in the Galápagos Islands for five weeks, during which Darwin accumulated plants and animals, focusing on the many birds. He thought he was collecting blackbirds, wrens, and warblers, but when he got them back to London, an ornithologist told him that though the birds looked different they were all finches. Plus Darwin had stored birds in bags by type and hadn’t separated much of his collection by island, which he later found was important. He’d assumed they were the same species he’d seen on mainland South America.
    He did notice that the mockingbirds he’d taken on the second island seemed different from the ones on the first, so he started labeling them. When the vice governor of the islands told Darwin that he could distinguish the tortoises on one island from the tortoises on another, Darwin ignored him at first. Darwin did not imagine that these animals could have originated from a few animals blown across the Pacific and that they had diversified into different species on different islands within clear sight of one another. Darwin held, as did many scientists at that time, that these animals were all the same. Differences in color and form were indicative of different varieties, not separate species.
    The definition of a species, according to Ernst Mayr, a German-born American biologist, is “groups of interbreeding natural populations reproductively isolated from other such groups.” This definition didn’t seem to fit the samples of wildlife Darwin had collected. These islands were in sight of one another. Surely separate species could not form on places so close. But they had