Dawkins: Randy, you and I are both Darwinians, obviously,
but you're a medical doctor, and I'm not.
It's always struck me that a lot of medical
doctors don't seem quite to have caught up,
150 years after the origin, is that your impression too?
Nesse: They're all very interested once they
find out about it, but, very few doctors
have had the chance to get an education in
evolutionary biology, and boy do I ever wish I had! Dawkins: Yes! (laughter)
Nesse: When I was getting my medical education
there were so many things that would have
made a lot more sense, if someone had just
really explained how natural selection works.
Dawkins: There are some doctors who feel
"Well all I need do then is to learn about
a lot of other animals as though I was a vet,"
but it's not quite like that, is it?
Nesse: No. We really need to know where
they all came from, and why they're all
designed in ways that make things go wrong.
Dawkins: So you use the word design there
Dawkins: and we need, obviously, to interpret that Nesse: Yes.
Dawkins: in the special Darwinian sense of 'design.' Nesse: You know I always end up using
the word design, and someone in the audience
always said, "You shouldn't do that, Dr. Nesse!
Because you don't really mean 'design!'"
And they're absolutely right of course.
Dawkins: Well, yes, but we've grown out of
that now, haven't we? Or have we not?
Nesse: But when you look at how the mechanisms
of the body work, it's almost automatic
to talk about them being designed. What
really gives the proof is when you look at how
badly designed they are. No sensible person
would have ever left the body the way it is.
Dawkins: Like what? Whats a good example of that?
Nesse: Name your part of the body that you want to.
Probably a lot of people watching this show
have been on a skateboard. And, for instance,
they fall like this, and they break these bones here.
The doctors call it a 'colles' fracture.
If you look on the skeleton, it's these two bones
fracture right there. Now, people have been falling
down like that, for, you know, a million years
or our predecessors have. Why didn't natural
selection make these bones thicker? And the answer
is this; we can do this marvelous thing of
rotating our arms all the way around, like that,
I won't do it with this model because it's a
Victorian skeleton, it's quite delicate. But notice
how those bones go across each other. If those
bones were thicker, it would be more like this...
(Grunting noises)
And then you couldn't throw...
So, it's a trade off, isn't it?
Now, this is something that any machine
would be limited by. But, when they make robots,
they still are not using two different firm
rods usually. There is usually one that rotates.
Dawkins: Ok, so it's kind of a historical legacy then?
Nesse: That's the other part of it, yes, exactly.
"Historical Legacy," the technical term is
"Path Dependance," it's all the same. Probably
a lot of viewers have a keyboard for their
computer, and we all have what's called a
"qwerty keyboard." And that keyboard was
designed specifically to keep typewriter
keys from sticking. And so they put all the
vowels a fair way away from each other so
there was a little delay. Well this means
we all type slowly because our keyboards
are designed to make us type slowly.
Dawkins: There are better designs of keyboard. Nesse: There are. What's it called... 'The Dvorak'?
Dawkins: Yes, and once you've learned how to do it you go faster, don't you?
Nesse: You first. The time it takes to learn...
RD: Exactly, exactly. I will never do that.
Nesse: I think the world may be stuck with Dawkins: Yes.
Nesse: these maldesigned keyboards for another
100 years just because they started off that way,
and the cost of changing is too high for all
of us, so were stuck with it. Likewise, there are
all kinds of aspects of the body that might
be done differently, but we've gone down
one particular path and can't get out of it.
Dawkins: The example I like to use with
machines is imagine if you had to evolve the
jet engine from the propellor engine by
Dawkins: changing it one little step at a time. Nesse: Not possible!
Dawkins: Or if you did you would have a pretty lousy jet engine!
Nesse: Exactly so. Dawkins: What are other examples in the human body?
Nesse: The most dramatic is the human eye.
You know, it's held up as this example of
perfection in the body, it's not perfect at all!
It's the perfect example of why the body is not designed.
Imagine a camera designer for a famous
camera company like Nikon or Pentax who
put the wires between the light and the film,
which is how our eye is working. And not only that,
our eye has a whole blind spot where
nothing works at all. Do you know that every
Nesse: creationist has a blind spot? Dawkins: (laughter)
Dawkins: I think it was Helmholtz, the famous
German psychologist who said, if somebody had,
if an engineer had given him the
human eye, he'd have sent it back.
Nesse: Indeed, indeed. I think viewers might
like to see their own blind spot, shall we
Nesse: demonstrate for them for just a moment? Dawkins: Ok.
Nesse: All you need to do the demonstration is
a little pencil, you can do it just with an eraser,
but this particular one has a little tiny red
pin in the top. And what you do is, cover one
eye if you would please. And we take the pin
and we move it right- You have to keep looking right
at the bridge of my nose, so keep your eye fixed.
And now were going to move it just out a
little bit, about 15 degrees. And right about there...
Dawkins: Yup, it's gone. Nesse: It's gone? You can't see it?
Dawkins: No. Nesse: Now can you see it?
Dawkins: Yes. Nesse: Now can you see it?
Dawkins: No. Nesse: There's a blind spot. That's really lousy!
Dawkins: Yeah. Nesse: So, whats amazing though about how
Nesse: natural selection has made the eye so it
works despite this built in flaw is that the eye
constantly jiggles slightly. We call it "nystagmus."
And this seems like it's a problem, but it's
actually a solution. Because if it wasn't for the
eye jiggling constantly, just a little bit, that
blind spot would always be in the same spot
and you'd never see anything there. But because
the eye moves slightly, you end up getting
Nesse: a complete coverage of your field of vision. Dawkins: It is remarkable how natural selection
Dawkins: manages to kind of clean up afterwards, isn't it?
Nesse: Thats a lot of what it does. Dawkins: You start off,
Nesse: It's stuck with things. Dawkins: It's stuck with things by historical
Dawkins: accident but then the cleaning up
afterwards is so good that it actually ends
up as a really remarkably fine instrument,
despite its historical legacy.
Nesse: And with the eye there are other things that happen later in life, like
detached retinas. For us, as I said, all of the
vessels and nerves come through that
hole in the back of the eye ball, that's why
there's a blind spot, and they spread out
on the inside of the eyeball between the light
and the place where the light is received,
blocking the light. And that's why you have to
have that little bit of "jiggle" in there. But, that's
for all mammals, in fact all vertebrates. Not all
species have this problem, interestingly. And If
we can go over here to our octopus, I don't know
if you can zoom in? All of the octopuses, the cephalopods,
have an eye that's designed properly. There, I used
the design word again. Their eyes have all of the
vessels and nerves coming right through the
back of the eyeball so they cant get a retinal
detachment, they never have a problem with
a blind spot, they don't have to be moving the
eye so much to get a complete field of vision,
it's a better design, absolutely entirely than ours,
and the reason is... Why are we so "screwed up"?
Nesse: Bad luck. There's no other Dawkins: Yup.
Nesse: explanation, except it's bad luck. Dawkins: Never the less, we probably see
Dawkins: better than octopuses do because
Dawkins: our cleaning up has been so thorough. Nesse: Or differently, you know?
Dawkins: Yes Nesse: That's another example of "trade offs."
For instance, an eagle can see a mouse
Nesse: from half a mile away, and we can't. But, Dawkins: Yes.
Nesse: they don't have the color vision that we have,
they don't have the field of vision we have.
Everything in the body, once you take an
evolutionary view, is "trade offs" all the way down.
Dawkins: So you're kind of answering the
question of why the body goes wrong and
there are all sorts of reasons why it goes wrong.
What other aspects are there of Darwinian
Dawkins: medicine that doctors ought to know about? Nesse: I should emphasize that this field
Nesse: really got going by a collaboration of mine
with George Williams. Viewers may or may not
know he's one of the more famous and
worthy evolutionary biologists of our time. Right, right.
And it's very closely related to your work on
"Selfish Genes," of course, because prior to
Williams' work in 1966, most people thought
that natural selection shaped species for their
own good. Now we know that selection works
much more strongly at the level of the gene. So, that
theme has infused a lot of my work with George Williams,
but as we started talking, in our collaboration
about why the body isn't better designed, we finally
narrowed it down to six possible reasons.
I'm using the word design over and over again.
Dawkins: Go ahead! Nesse: I can see why other people do, you know?
Nesse: It's very hard to find another word to
refer these mechanisms that work so well.
Dawkins: I mean, once and for all, it looks
like design, natural selection produces a
Dawkins: powerful illusion of design. Nesse: They work.
Dawkins: You've just been telling us some
reasons why it's actually not entirely a good
analogy because there are imperfections
which no human designer would tolerate.
Nesse: And maybe we should pause at this
moment to ask if the body is a machine? I was
Nesse: taught, certainly, that the body is a machine. Dawkins: I always used to say it was a machine.
Nesse: Yes. But that's a metaphor which is fundamentally wrong.
The body is not a machine. It works very well,
it has levers, and pulleys, and connections,
and all the rest, but a machine has blueprints,
one master design and a manufacturing process
that moves from the blueprint to the finished version,
which is all the same. There are no blueprints for
the body. There's a genome that has information
in it, but some people imagine that the genome,
that there is a normal genome. There is no normal genome!
There are only genes. And those genes that
make bodies that end up reproducing more
than others, they go on and become more
frequent in the future. Other genes become less
frequent and are gone. The genome is a collection
of genes that work. It's nothing like a blueprint.
Dawkins: No, it's certainly nothing like a blueprint.
I still think that in some respects it's reasonable
to talk about the body as a machine. In other
respects it's not. I mean, its not designed,
it doesn't have a blueprint. On the other hand,
there's a mechanism... A heart is a pump, an eye
is an image forming device, with all sorts of
respects in which it resembles a camera, an iris
diaphragm that narrows down and so on.
I mean, it's kind of a machine, but it's a
different sort of machine, and above all,
it has a different history.
Nesse: Exactly so. And, the other evidence that
it's not a machine is that a machine can be
changed completely by the designer.
RD: Back to the drawing board. RN: Right.