ANDREA SEABROOK, host:
Your hand, notably your thumb, is part of what makes you human. But if you look even closer at your hand, you might catch a glimpse of your inner fish.
On today's Science Out Of The Box, we discover our inner fish with paleontologist Neil Shubin. He's the author of the new book, "Your Inner Fish: A Journey into the 3.5-Billion-Year-History of the Human Body."
Dr. NEIL SHUBIN (Paleontologist): Carl Sagan once famously said that looking at the stars is like looking back in time. The star's light began the journey to our eyes eons ago, long before our world was formed.
I like to think that looking at humans is much like peering at the stars. If you know how to look, our body becomes the time capsule that when opened tells of critical moments in the history of our planet and of its distant past in ancient oceans, streams and forests.
SEABROOK: Neil Shubin joins me now to delve into our collective human past. Professor Shubin, thanks very much for speaking with us.
Dr. SHUBIN: Thanks for having me on.
SEABROOK: Listeners may remember your name, actually - I want to remind them - from your famous discovery, tiktaalik. Is that - am I pronouncing that right?
Dr. SHUBIN: You said it right, exactly.
SEABROOK: Tiktaalik, the link - a link between fish and land animals. Tell us about tiktaalik.
Dr. SHUBIN: Well, if I put tiktaalik in front of us right now, what you would see is an animal about four feet to nine feet long. We have many specimens of it.
SEABROOK: Mm-hmm.
Dr. SHUBIN: But the first would strike you is it has scales like a fish. It even has fin webbing like a fish. Then something would strike you as odd. It has a flat head with eyes on top, much like early land living animals from about 365 million years ago. It has a neck. No fish has a neck. And when you open the fin up and you go inside that fin webbing, what you see are elements that correspond to our shoulder, our elbow and wrist, even parts of our palm. It's part fish, part early land living animal of about 375 million years old.
SEABROOK: I think that is just so cool, especially the part about the wrists and - dare I call it - leg thing.
Dr. SHUBIN: Yeah. I mean, what we have with this tiktaalik is a fish with fins, but inside that fin is a part of our own limb, really. And it allowed that creature to do a form of a push up. It even had a little palm with a wrist, so that it could push its body off the ground.
SEABROOK: So let's look at our hands here. I want to sit here and look at my hand. I'm familiar with how the bones look if I were to put my hand under an x-ray machine. So which bones in there correspond to which bones in your fish-a-pod, tiktaalik?
Dr. SHUBIN: Okay. So start with your upper arm. The upper arm, your humorous, the one bone you have there?
SEABROOK: Mm-hmm?
Dr. SHUBIN: That's in tiktaalik. Then go to your elbow. That whole joint is in tiktaalik. In fact, the two bones that make up your forearm, they're in tiktaalik as well. Now look at your arm and bend your wrist back and forth, back and forth.
SEABROOK: Bank and forth.
Dr. SHUBIN: What you have are a series of about eight bones that allow you to do that. And they bend in certain predictable ways. Four of those are known in tiktaalik.
SEABROOK: Wow.
Dr. SHUBIN: And then take your fingers and just jiggle them around and around and what you have are little bones that correspond to parts of our fingers.
SEABROOK: One of the things that I love about this book is that thinking about our bodies this way explains a lot of the quirks about our bodies. I mean, why we get hiccups, for example.
Dr. SHUBIN: Yeah. You know, if you look at - you know, what's a hiccup? A hiccup is - (makes hiccup sound) - that sort of thing. When you do that - (makes hiccup sound) - that is, basically what you're doing is your closing the glottis, which is the little flap at the back of your throat, and you're doing a really sharp inspiration. And the reason why you do that is there's an irritation that causes in your brainstem a certain set of neurological patterns that cause a stereotypical pattern of muscles firing in your abdomen, your throat, and so forth.
Well, you can go looking around in other animals and see, well, who else has this pattern in the brainstem? And it turns out you find it in creatures that breathe with both gills and lungs. It's seen in tadpoles. And they actually breathe with a form of a hic - a form of a hiccup.
And so it's really remarkable that, you know, this nascent capacity, which was useful in creatures like tadpoles, comes out in us in odd circumstances.
SEABROOK: So you see in the human body these relics of our own evolution?
Dr. SHUBIN: Yeah, it's very beautiful. I mean, really, when you see our own history. You - it's like peeling an onion, you know? I mean, you know, first you see our - the past we share with other mammals. Then you see the past we share with reptile-like things. And then fish and worms, and it even goes all the way back to jellyfish and sponges, when you look at the DNA that builds our bodies. I mean, it's just hard not to see our bodies as just 3.5 billion years of history - in every organ, in every cell, in every piece of DNA in our bodies.
SEABROOK: Professor Neil Shubin is associate dean of the medical school at the University of Chicago, as well as the provost of the Field Museum of Natural History. Thank you, sir, very much for speaking with us. Transcript provided by NPR, Copyright NPR.
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