Published on Nov 8, 2014
Extinction happens. But what’s evolution got to do with it?
Mass extinctions. Dinosaurs and the first mammals. Saving an unspoiled forest near Bangkok. Biological invaders in the Hawaiian Islands. Using a beneficial insect to control weeds in North Dakota.
“Extinction is the termination of a species.” At least 95 per cent of all species that have ever lived are now extinct. Extinction is normal, and is happening all the time, at the rate of a few species per year.
We watch various animals foraging for food, and a lioness bringing down her prey. “The extinction of old species that can no longer adapt or compete creates opportunities for new species that can–in an endless cycle,” the narrator says. “So evolution and extinction are in balance. But what happens when a planet-wide catastrophe strikes and a great dying begins?”
The scene changes dramatically–to lightning, volcanoes, and fire. Five times in the last half-billion years, we are told, mass extinctions wiped out most species alive at the time. As the smoke clears, we see Peter Ward driving through South Africa to investigate the greatest of these mass extinctions–the one that occurred at the end of the geological period known as the Permian. He stops at an old abandoned farmhouse, and sees from the tombstones in a nearby graveyard that the family that used to live there died within a five-year period about a century ago. “So a hundred years [ago], these people were just wiped off the face of the Earth, and we have no idea what killed them,” says Ward. “And if that’s the case, how am I going to figure out what killed animals that lived in those hills [gesturing], the fossils of which we have from 250 million years ago?”
In the rocks of those hills, Ward finds evidence that a great catastrophe occurred at the end of the Permian. “So catastrophic was that mass extinction,” says Ward, “that even the small creatures have died out. It’s not just the mighty, it’s the meek.” An animation shows us what might–or might not–have caused the Permian extinction. “When species died, they didn’t die alone,” says the narrator. “The collapse of one helped bring down the others.”
Ward explains: “You could almost analogize that to a house of cards. Each species props up another, in a sense.” We watch as a huge house of playing-cards teeters in front of us. Ward continues: “Because the creature that you eat is that card that is sitting under you that gives you your energy. Now let’s pretend that we start kicking out card after card after card–and that’s what a mass extinction does, isn’t it? It starts knocking out a species here, it knocks out a species there, but pretty soon lots of species are gone. And it’s not just the disappearance of species now–the whole house of cards falls down.”
Not everything died in the Permian extinction, however. Ward holds up the skull of a mammal-like reptile. He says that the few lineages that survived the extinction “start evolving, because the world is empty, and empty worlds really begat [a] tremendous amount of evolutionary diversifications.”
But how do empty worlds beget new species, exactly? Mass extinction may be an important feature of the history of life; but the question is, how did living things diversify afterwards? That is the question Darwin’s theory is supposed to answer, but the fact of extinction doesn’t help us. Species go extinct, and new ones take their places. This may come as a surprise to people who believe that species never go extinct (if, in fact, there are such people); but how does it provide evidence for Darwinian evolution?
happen to the Dinosaurs?