Extinction is a fairly new concept in human thought. Shelley Emling explains in The Fossil Hunter:
For centuries, Christians were convinced that Genesis told the true story of creation. Fossils only reinforced the biblical account. For example, some fossils were found at such high altitudes that people thought they must surely have been deposited there as a result of the worldwide flood depicted in Genesis....After all, the Bible stated that God created the heavens and the earth and every living thing in it in just six days. There was never any mention of a prehistory and therefore never any mention of prehistoric animals....In general, very few people doubted the Bible's veracity.
Today people argue against evolution by citing the Bible, and 300 years ago they argued against extinction citing that same source. The world, they said, was exactly as God had made it 6,000 years before and it hadn't changed since then.
But the fossils kept coming. In England, Mary Anning and others were digging up ichthyosaurs and pleisiosaurs and other fossils that didn't look like anything living. In Siberia, Russians were finding woolly mammoths. And in the United States, Americans were digging up mammoths and mastodons. Richard Conniff writes in the April issue of Smithsonian:
The discovery of such monstrous creatures raised troubling questions. Cuvier made the case that both mammoths and mastodons had vanished from the face of the earth; their bones were just too different from any known pachyderm. It was the first time the scientific world accepted the idea that any species had gone extinct—a challenge to the doctrine that species were a permanent, unchanging heritage from the Garden of Eden. The disappearance of such creatures also cast doubt on the idea that the earth was just 6,000 years old, as the Bible seemed to teach.
In fact, mammoths and mastodons shook the foundations of conventional thought. In place of the orderly old world, where each species had its proper place in a great chain of being, Cuvier was soon depicting a chaotic past in which flood, ice and earthquake swept away “living organisms without number,” leaving behind only scattered bones and dust.
Eventually the evidence was overwhelming—there were thousands upon thousands of creatures that no longer existed. Extinction was reality and no one argues otherwise anymore. In fact, we now know that the rate of extinction has changed over time and reached five peaks called mass extinctions (the most familiar will be the Cretaceous-Tertiary extinction event, 65 million years ago, which wiped out the dinosaurs). We may be on our way to a sixth.
But how can people have come to understand that extinction is real—and thus God's world must have changed and is doing so before our very eyes—but still think that evolution is bunk? I don't have an easy answer to this (and if any creationists stumble upon this, please explain your views in the comments below), but it might have something to do with the nature of the evidence. It is easier to believe that creatures have ceased to exist, especially when you can see that happening right now, than it is to visualize the path from, say, Ardi to humans. Evolution is a slow process that takes place over long periods of time, and the bits we can see—like the changes in flu viruses from year to year or a single bird species slowly diverging into two—can be easy for some to dismiss. That extinction became an accepted concept gives me hope, however, that more people may one day accept evolution as well.