Wednesday, July 30, 2008
From T-Rex to Tweety?
One objection to evolution that I hear among my friends (mostly white, mostly middle class, mostly Christian) runs something like this: "I don't have any problems with microevolution. The Creator would have to make animals so that they can adapt. What I do have problems with is evolution from one species to another. I mean, that's just impossible. Look around. You don't see birds turning into monkeys or dogs turning into elephants. It just doesn't happen."
I've been pondering that objection and how to answer it from the scientific evidence, and I've come up with an angle. I'll be interested in feedback on this approach, especially since I'm at the point in the book where I'm going to need to address this issue. My answer to that objection, however, has to do with the massive amounts of time involved in evolution. I know that's a mind-bender for many Christians who come from a young-earth viewpoint. I wonder if time causes the same issue for people form other religions.
To understand how new species develop, I had to look back to the past. You can't look around now. Our short lives (75 or so years) and our short human history (3000-4000 years) don't stretch long enough to see speciation occurring in any way that we will ever be able to say, "Oh, I see a new species over there." Instead, we have to look back over the fossil record to see large periods of time when new species are evolving.
An example of this would be to look back at the end of the dinosaur age to see how animals very different than the dinosaurs evolved from them. As best I understand, it goes something like this: During the time of the dinosaurs, they evolved until they were many kinds of dinosaurs roaming around. One group was the maniraptors, whose wrists were different than those of other dinosaurs. Over a long period of time, this group of dinosaurs got more varied. The fossil record shows that it included Velociraptors and their relatives (of Jurassic Park fame), Oviraptors (who took care of their eggs), the group called Troodontidae (thought to be pretty dang smart for a dinosaur), and birds. That last word, "birds," may be surprising to you. It was to me as I did the research to write this post. I didn't realize that birds were classified right there as members of the dinosaur family. (If you want to know more, take a look at the page on Coelurosauria in the Tree of Life project. That website can be a little tricky to learn how to move around. Make sure to see the "Containing Group" link below the list of species. It's what lets you go backwards, that is earlier along the fossil record.) And, if you look at Birds (technically Aves from the Latin), you'll see that they contain Archaeopteryx, which most people think of as a dinosaur.
So what? Well, back to the original objection. "I've never seen animals evolve!" If I'm reading the fossil record right, here's a time where we see one animal evolving into a very different one. A dinosaur became a bird!
But, the clever reader will realize that the statement I just made--dinosaurs becoming birds--is the wrong way to state it. That's not really what happened at all, according to the fossil record. During the millions and millions of years that dinosaurs were on the earth, they evolved into a huge variety. One small group out of this was what we think of as birds. And, natural selection kicked in here at the end of the age of dinosaurs. When whatever happened to wipe out the dinosaurs occurred, the early birds were different enough that they were able to survive under the new conditions and begin to evolve into the vast variety of birds we have today.
Does that make any sense? The way I see it is that we'll never actually see the macroevolution that many people object to because we live such short lives. But, if we look back over the fossil record, we can see species change into totally different kinds. I don't really expect religious kids to believe that this is how the Creator made birds, but I do want them to see how science explains the fossil record.
By the way, if you want a little challenge, try using the Tree of Life to trace Mammals (i.e. Mammalia) back to find out when they and the dinosaurs diverged from each other. I'll give you a hint--what fluid surrounds a baby during pregnancy? If you find the answer, you should also see where turtles and reptiles split off.
(The T-Rex skull is from the collection of the Lawrence Hall of Science. I took the picture.)