there are occasional very occasional
random changes called mutations those
varieties of DNA that just happened to
be good at building ancestors and
building bodies that have good eyes good
legs good anything else survived so the
world automatically becomes filled with
good DNA this means good at making
bodies that are themselves good at
surviving now I want to apply this
lesson to three particular cases three
particular problems that have given
difficulty the eye the wing and
camouflage and I choose them because
they're famously regarded as difficult
first the eye well suppose we start with
an ancestor who didn't really have an
eye at all but just a single simple
sheet of light-sensitive cells that's
represented by this screen here and
there's a television camera behind
looking at the screen so that we on the
screen on the television screen shall
see what this primitive animal would see
so this animal with hardly any eye at
all will at least be able to tell the
difference between light and dark light
and dark now the next stage in evolution
would be to have a shallow cup this
animal would be able to tell the
direction that light is coming from
because their shadow would appear shadow
would appear there and if you can tell
the direction a light is coming from
then you can tell the direction that a
predator is coming from now although
we've represented this as a cup coming
out from the wall it would in fact
probably be an indentation and it would
be a gradual indentation it's in candy
to make a gradual indentation it has to
be made as a rather abrupt cup that
comes out six inches at a time but it's
easy to see that that shadow effect that
we've just been witnessing would work
progressively and gradually as the cup
gets bigger let's make it bigger still
now risin and this cup is even more
effective and if we go on to the next
stage where we make the cup gradually
bigger again so big that it becomes just
a little hole in the end right now this
animal has a very good idea of exactly
where the light is and by the same token
exactly where for example a predator is
and I think with this eye we might even
get a little image see if we can get an
image of Bryson's hand that smudge there
is Bryson's hand and you can just about
see a very dim image of his fingers so
an animal with an eye like this would be
able to see perhaps just a little bit
what kind of predator it was let's go to
the logical conclusion which would be a
pinhole remember with his all gradual
gradual change in evolution right let's
see if we can see your hand again Bryson
now I can see a rather precise picture
of Bryson's hand is not a very bright
one but I can see every finger clearly
delimited so I could see if I were this
animal I could see my predator in some
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