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.)

9 comments:

Anonymous said...

Lee,

A cool website and a great explanation. The micro/macro evolution distinction is really a red herring. Macroevolution is just lots of microevolution given enough time.

--Jeff

Anonymous said...

Hi Lee. I haven't had time to look at the sites you mentioned but a question has popped into my mind...is the conversation on evolution restricted to animals & plants only or humans in the context of animals evolving into humans?

Anonymous said...

That last comment was from J. Malone by the way.... :o)

Anonymous said...

I am not convinced about the dinosaur and bird link (for a variety of reasons). One of them being the expression of genes being significantly different. They may have many of the same genes like humans and apes, but the expression of said genes makes them different. At this point in the evolutionary time scale would be safe to assume that many safegaurds would have been put around the DNA to prevent mutations and new expressions of genes that were non functional or "blocked"? IF so how would one overcome those safeguards. The second thing is in regards to the bones and muscles. Bone/muscle similarity does not have to equal a relationship that proves a connection. With the lack of fossil evidence from the Triassic era it appears they started to evolve and diversify by natural selection quite quickly. Could it be that they either convergently evolved similar structures from another related ancestor or evolved from another group?

josh

Anonymous said...

Josh,

What do you mean by "At this point in the evolutionary time scale would be safe to assume that many safegaurds would have been put around the DNA to prevent mutations and new expressions of genes that were non functional or "blocked"?"" My knowledge of DNA is pretty scanty, but the idea of safeguards preventing mutations is new to me.

Thanks,
Jeff

Lee said...

Anon/JMalone: We can talk about human evolution if you'd like, but of course, that makes the conversation a lot stickier for people who believe that humans were specially created by God. I've decided personally to take on human evolution and look at the fossil evidence for early humans. I'm finding that there's a lot out there, and it's made my understanding of Genesis a little murky.

I'm not planning to deal with it in my book, though, because I'm going to advise teachers that human evolution is probably just way too big of an issue for students in grades 6-10. The book is targeted at teachers of that level students.

Lee said...

Josh: Honestly, you've got me. I'm not sure about your questions, and I hope someone else can help us out. You're thinking about the evidence, though, and that's my main point in all of this. I want religious people, including students, to be able to look at the evidence and think it through like you did.

Did I read your comment right, though? You didn't seem to be question that birds evolved, but the actual mechanism of how they evolved.

Anonymous said...

jeff,

There are several mechanisms inside the cell to prevent damages(mutations) to the DNA. For instance there is an enzyme (in the DNA polymerase family) that I like to call the proofreader. At any given time your DNA in your cells is either being repaired because of environmental damage or it is being replicated. This proofreader checks to make sure that A = T and G=C in DNA. Its whole existance is to prevent further mutation of the genetic code. There are other enzymes or proteins that exist to prevent malformation of mRNA and therefore incorrect proteins/enzymes. We are just now discovering even more of these safeguards and on/off switches (RNAi). These are just a few examples of the way the cell keeps the status quo. The cell will fight every mutation it can find in an attempt to prevent/fix mutations. It would be very difficult to acquire new genes through mutations because of these safeguards. If we never get new genes or get the ability to turn on/off genes then how does one evolve?

lee,

As a young earther (is that even a word :-) ) I take the position that birds and dinosaurs are different "kinds" as genesis would say and therefore not evolutionary related. However, birds have evolved and diversified since that original momemnt in time. I question not whom they have evolved from but the how.

josh

Seema said...

Thanks for writing this.