What we didn't know about male anatomy | Diane Kelly

1,220,501 views ・ 2012-06-05

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Translator: Timothy Covell Reviewer: Morton Bast
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When I go to parties,
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it doesn't usually take very long
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for people to find out
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that I'm a scientist and I study sex.
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And then I get asked questions.
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And the questions usually have a very particular format.
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They start with the phrase,
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"A friend told me,"
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and then they end with the phrase,
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"Is this true?"
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And most of the time
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I'm glad to say that I can answer them,
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but sometimes I have to say,
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"I'm really sorry,
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but I don't know
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because I'm not that kind of a doctor."
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That is, I'm not a clinician,
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I'm a comparative biologist who studies anatomy.
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And my job is to look at lots of different species of animals
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and try to figure out how their tissues and organs work
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when everything's going right,
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rather than trying to figure out
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how to fix things when they go wrong,
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like so many of you.
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And what I do is I look for similarities and differences
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in the solutions that they've evolved
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for fundamental biological problems.
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So today I'm here to argue
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that this is not at all
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an esoteric Ivory Tower activity
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that we find at our universities,
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but that broad study
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across species, tissue types and organ systems
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can produce insights
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that have direct implications for human health.
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And this is true both of my recent project
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on sex differences in the brain,
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and my more mature work
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on the anatomy and function of penises.
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And now you know why I'm fun at parties.
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(Laughter)
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So today I'm going to give you an example
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drawn from my penis study
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to show you how knowledge
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drawn from studies of one organ system
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provided insights into a very different one.
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Now I'm sure as everyone in the audience already knows --
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I did have to explain it to my nine-year-old late last week --
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penises are structures that transfer sperm
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from one individual to another.
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And the slide behind me
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barely scratches the surface
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of how widespread they are in animals.
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There's an enormous amount of anatomical variation.
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You find muscular tubes, modified legs, modified fins,
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as well as the mammalian fleshy, inflatable cylinder
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that we're all familiar with --
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or at least half of you are.
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(Laughter)
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And I think we see this tremendous variation
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because it's a really effective solution
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to a very basic biological problem,
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and that is getting sperm in a position
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to meet up with eggs and form zygotes.
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Now the penis isn't actually required for internal fertiliztion,
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but when internal fertilization evolves,
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penises often follow.
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And the question I get when I start talking about this most often is,
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"What made you interested in this subject?"
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And the answer is skeletons.
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You wouldn't think that skeletons and penises
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have very much to do with one another.
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And that's because we tend to think of skeletons
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as stiff lever systems
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that produce speed or power.
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And my first forays into biological research,
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doing dinosaur paleontology as an undergraduate,
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were really squarely in that realm.
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But when I went to graduate school to study biomechanics,
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I really wanted to find a dissertation project
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that would expand our knowledge of skeletal function.
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I tried a bunch of different stuff.
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A lot of it didn't pan out.
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But then one day I started thinking
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about the mammalian penis.
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And it's really an odd sort of structure.
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Before it can be used for internal fertilization,
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its mechanical behavior has to change
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in a really dramatic fashion.
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Most of the time it's a flexible organ.
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It's easy to bend.
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But before it's brought into use
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during copulation
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it has to become rigid,
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it has to become difficult to bend.
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And moreover, it has to work.
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A reproductive system that fails to function
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produces an individual that has no offspring,
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and that individual is then kicked out of the gene pool.
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And so I thought, "Here's a problem
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that just cries out for a skeletal system --
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not one like this one,
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but one like this one --
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because, functionally,
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a skeleton is any system
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that supports tissue and transmits forces.
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And I already knew that animals like this earthworm,
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indeed most animals,
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don't support their tissues
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by draping them over bones.
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Instead they're more like reinforced water balloons.
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They use a skeleton that we call a hydrostatic skeleton.
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And a hydrostatic skeleton
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uses two elements.
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The skeletal support comes from an interaction
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between a pressurized fluid
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and a surrounding wall of tissue
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that's held in tension and reinforced with fibrous proteins.
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And the interaction is crucial.
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Without both elements you have no support.
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If you have fluid
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with no wall to surround it
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and keep pressure up,
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you have a puddle.
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And if you have just the wall
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with no fluid inside of it to put the wall in tension,
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you've got a little wet rag.
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When you look at a penis in cross section,
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it has a lot of the hallmarks
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of a hydrostatic skeleton.
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It has a central space
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of spongy erectile tissue
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that fills with fluid -- in this case blood --
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surrounded by a wall of tissue
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that's rich in a stiff structural protein called collagen.
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But at the time when I started this project,
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the best explanation I could find for penal erection
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was that the wall surrounded these spongy tissues,
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and the spongy tissues filled with blood
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and pressure rose and voila! it became erect.
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And that explained to me expansion --
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made sense: more fluid, you get tissues that expand --
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but it didn't actually explain erection.
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Because there was no mechanism in this explanation
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for making this structure hard to bend.
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And no one had systematically looked at the wall tissue.
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So I thought, wall tissue's important in skeletons.
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It has to be part of the explanation.
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And this was the point
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at which my graduate adviser said,
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"Whoa! Hold on. Slow down."
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Because after about six months of me talking about this,
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I think he finally figured out
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that I was really serious about the penis thing.
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(Laughter)
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So he sat me down, and he warned me.
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He was like, "Be careful going down this path.
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I'm not sure this project's going to pan out."
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Because he was afraid I was walking into a trap.
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I was taking on a socially embarrassing question
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with an answer that he thought
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might not be particularly interesting.
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And that was because
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every hydrostatic skeleton
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that we had found in nature up to that point
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had the same basic elements.
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It had the central fluid,
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it had the surrounding wall,
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and the reinforcing fibers in the wall
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were arranged in crossed helices
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around the long axis of the skeleton.
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So the image behind me
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shows a piece of tissue
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in one of these cross helical skeletons
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cut so that you're looking at the surface of the wall.
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The arrow shows you the long axis.
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And you can see two layers of fibers,
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one in blue and one in yellow,
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arranged in left-handed and right-handed angles.
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And if you weren't just looking at a little section of the fibers,
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those fibers would be going in helices
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around the long axis of the skeleton --
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something like a Chinese finger trap,
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where you stick your fingers in and they get stuck.
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And these skeletons have a particular set of behaviors,
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which I'm going to demonstrate in a film.
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It's a model skeleton
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that I made out of a piece of cloth
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that I wrapped around an inflated balloon.
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The cloth's cut on the bias.
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So you can see that the fibers wrap in helices,
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and those fibers can reorient as the skeleton moves,
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which means the skeleton's flexible.
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It lengthens, shortens and bends really easily
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in response to internal or external forces.
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Now my adviser's concern
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was what if the penile wall tissue
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is just the same as any other hydrostatic skeleton.
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What are you going to contribute?
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What new thing are you contributing
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to our knowledge of biology?
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And I thought, "Yeah, he does have a really good point here."
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So I spent a long, long time thinking about it.
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And one thing kept bothering me,
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and that's, when they're functioning,
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penises don't wiggle.
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(Laughter)
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So something interesting had to be going on.
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So I went ahead, collected wall tissue,
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prepared it so it was erect,
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sectioned it, put it on slides
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and then stuck it under the microscope to have a look,
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fully expecting to see crossed helices of collagen of some variety.
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But instead I saw this.
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There's an outer layer and an inner layer.
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The arrow shows you the long axis of the skeleton.
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I was really surprised at this.
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Everyone I showed it
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was really surprised at this.
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Why was everyone surprised at this?
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That's because we knew theoretically
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that there was another way
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of arranging fibers in a hydrostatic skeleton,
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and that was with fibers at zero degrees
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and 90 degrees to the long axis of the structure.
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The thing is, no one had ever seen it before in nature.
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And now I was looking at one.
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Those fibers in that particular orientation
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give the skeleton a very, very different behavior.
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I'm going to show a model
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made out of exactly the same materials.
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So it'll be made of the same cotton cloth,
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same balloon, same internal pressure.
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But the only difference
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is that the fibers are arranged differently.
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And you'll see that, unlike the cross helical model,
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this model resists extension and contraction
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and resists bending.
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Now what that tells us
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is that wall tissues are doing so much more
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than just covering the vascular tissues.
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They're an integral part of the penile skeleton.
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If the wall around the erectile tissue wasn't there,
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if it wasn't reinforced in this way,
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the shape would change,
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but the inflated penis would not resist bending,
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and erection simply wouldn't work.
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It's an observation with obvious medical applications
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in humans as well,
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but it's also relevant in a broad sense, I think,
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to the design of prosthetics, soft robots,
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basically anything
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where changes of shape and stiffness are important.
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So to sum up:
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Twenty years ago,
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I had a college adviser tell me,
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when I went to the college and said,
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"I'm kind of interested in anatomy,"
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they said, "Anatomy's a dead science."
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He couldn't have been more wrong.
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I really believe that we still have a lot to learn
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about the normal structure and function of our bodies.
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Not just about its genetics and molecular biology,
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but up here in the meat end of the scale.
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We've got limits on our time.
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We often focus on one disease,
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one model, one problem,
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but my experience suggests
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that we should take the time
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to apply ideas broadly between systems
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and just see where it takes us.
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After all, if ideas about invertebrate skeletons
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can give us insights
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about mammalian reproductive systems,
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there could be lots of other wild and productive connections
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lurking out there just waiting to be found.
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Thank you.
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(Applause)
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