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Evolution of Evolution — Home
Charles Darwin
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Evolution of Evolution — Text-only | Flash Special Report
Interview with Shannon Hackett and Sushma Reddy

Audio Transcript

BOBBIE MIXON:            During the last 150 years, a great deal has been made about Charles Darwin's trip to the Galapagos Islands, west of Ecuador.  There, he encountered a bird species commonly called Darwin's finches that would play an important role in explaining his theory of evolution.  The term “Darwin's finches” was popularized in a 1947 book by the same name, but Shannon Hackett and Sushma Reddy of the Field Museum of Natural History in Chicago say looks can be deceiving.  Darwin's finches aren't finches at all.  In fact, they say, much bird classification is wrong, made thornier by complicated bird evolution.  Dr. Reddy is a postdoctoral fellow at the Field Museum.  Welcome.

DR. SUSHMA REDDY:            Yeah.  Thank you. 

BOBBIE MIXON:            Dr. Hackett is the associate curator and head of the Field Museum's bird division.  Thanks for taking the time.

DR. SHANNON HACKETT:                        It's nice to be with you today.

BOBBIE MIXON:            Dr. Hackett, let me start with you.  If Darwin's finches aren't finches, what are they and how did Darwin get it wrong?

DR. SHANNON HACKETT:                  Actually, the DNA work that has been done shows that Darwin's finches are actually tanagers, brightly colored birds whose--there's a few representatives in North America--but who are mostly distributed in the New World Tropics, from Mexico down south, and it's not surprising that Darwin and the people who originally studied Darwin's finches got it wrong because if you look at many Darwin's finches, they look like finches.

BOBBIE MIXON:            Dr. Hackett, I just want to clarify something.  The misclassification really has no impact on our understanding of the process of evolution.  Would you say that's true?

DR. SHANNON HACKETT:                  I actually would not say that that's true.  I think the misclassification has a fundamental impact on our understanding of the process of evolution for these birds in particular and because, shockingly, also the traditional story that you might read in a textbook, for example, that story is not necessarily completely true and it's not accurate.  So, the story that you'll reading textbooks is that a poor group of woebegone finches, maybe in a storm, blew out over Ecuador and landed on the Galapagos Islands then, from there, diversified into the amazing array beak morphologies that you see today, including things that eat seeds, things that pick insects off of leaves, things that can poke tools into holes, but--and so that's a classic example of an adaptive radiation but the reality is that understanding where Darwin's finches came from, their position in the tree of life, has a huge impact on that particular process of adaptive evolution.

BOBBIE MIXON:            So are you saying that this--our understanding of adaptive radiation and the error associated with it could have extended to other species?

DR. SHANNON HACKETT:                  Yes, I'm saying it did.  Absolutely.

BOBBIE MIXON:            Dr. Reddy, let me turn to you.  You both are involved in a project that examines DNA from the major living groups of birds.  What's the project and what have you learned?

DR. SUSHMA REDDY:            So, we were interested in studying the bird tree of life, or the evolutionary history of birds, and so what we did--and this is a question that has long fascinated people because birds exhibit a really great diversity.  If you think of all the birds that you are familiar with, you see that there are these major groups, such as parrots or doves or owls, and they all look very different from each other but they're undeniably birds and what we're trying to figure out is how these different groups are related to each other, and so we had some sense of what we thought were how birds were related but for the--but for the most part, we didn't have a really good evolutionary tree for all the birds, and so our project was to take--was to use DNA sequences.  We collected more DNA sequences than any other project has for such a study and we were able to use these sequences to recover a really robust family tree of birds.

BOBBIE MIXON:            You also made some discoveries related to raptors--falcons and hawks aren't related?

DR. SUSHMA REDDY:            Yes.  So, from our study we found lots of unexpected results and one of them was that falcons and hawks, or birds of prey, are not closely related and this is surprising because these birds of prey have a lot of adaptations to their lifestyles that they have apparently evolved independently.  So, adaptations such as talons or sharp claws to catch their prey or forward facing eyes to give them good depth perception or sharp beaks to kind of rip the flesh off their prey items and it turns out for--traditionally we've always thought of falcons and hawks as being each other's closest relatives, but our study shows that they're actually not each other's closest relatives and that they independently evolved these features.

BOBBIE MIXON:            Dr. Hackett, a lot of bird classification is based on observation.  In fact, Charles Darwin was an accomplished observational scientist.  How could such keen observers misclassify so many species?

DR. SHANNON HACKETT:                  Well, that shows the power of adaptation to make things that look very, very similar when they need something to do a similar function.  So, you know, some of the power with which we study the tree of life now comes not just from observations because, certainly, the natural historian observers of the past did a very good job of understanding the basic biology of birds and their natural histories and behaviors, but now we have lots of different tools in our toolkit to study these things.  We can use very sophisticated algorithms to optimize the searching for trees. We can use different kinds of data, some that don't have the same constraints associated with adaptation that just a superficial observation of the outside of birds might give.

BOBBIE MIXON:            I want to throw this question to both of you.  Do you think, given the great diversity and variety, all birds have a single common ancestor?  Dr. Reddy?

DR. SUSHMA REDDY:            Yes, in fact, I don't think that question is that debated anymore.  We--the bigger question that we face is when the diversity of birds occurred and this is kind of leading to how they developed such a great diversity.

BOBBIE MIXON:            Dr. Hackett, thoughts?

DR. SHANNON HACKETT:                  I mean, one of the great things that I've learned about this through this project is that everything is a hypothesis to be tested.  So, do I think there's a single common ancestor bird?  Yes, I do.  I think the data that has come show that very clearly, but one of the great things about studies is that you always generate more questions than you actually answer, and so that's a question that additional data could play a role in addressing and so there could be additional data matrices, additional fossils that bear--that bear on that particular question.  So, you know, so that's one of the reasons why this kind of science is so exciting to us because, think about it, even in the year 2008, 2009, we have so much to learn about the bird tree of life.

BOBBY MIXON:            Dr. Shannon Hackett and Dr. Sushma Reddy with the Field Museum of Natural History in Chicago.  Thanks for joining us.

DR. SHANNON HACKETT:                  Thank you.

DR. SUSHMA REDDY:            Thank you.