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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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00:10:03,136 --> 00:10:04,886
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.

272
00:10:37,341 --> 00:10:40,941
After all, if ideas about invertebrate skeletons

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can give us insights

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about mammalian reproductive systems,

275
00:10:44,492 --> 00:10:48,541
there could be lots of other wild and productive connections

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00:10:48,541 --> 00:10:50,990
lurking out there just waiting to be found.

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Thank you.

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(Applause)