richard_dawkins_-_the_god_delusion

124 T H E G O D 1> E I U S I O N
illustrating, in practice, every step of the way up that particular
slope of Mount Improbable.
By analogy with the trees of different height, it is easy to imagine
situations in which half an eye would save the life of an animal
where 49 per cent of an eye would not. Smooth gradients are provided
by variations in lighting conditions, variations in the distance
at which you catch sight of your prey - or your predators. And, as
with wings and flight surfaces, plausible intermediates are not only
easy to imagine: they are abundant all around the animal kingdom.
A flatworm has an eye that, by any sensible measure, is less than
half a human eye. Nautilus (and perhaps its extinct ammonite
cousins who dominated Paleozoic and Mesozoic seas) has an eye
that is intermediate in quality between flatworm and human.
Unlike the flatworm eye, which can detect light and shade but see
no image, the Nautilus 'pinhole camera' eye makes a real image;
but it is a blurred and dim image compared to ours. It would be
spurious precision to put numbers on the improvement, but nobody
could sanely deny that these invertebrate eyes, and many others, are
all better than no eye at all, and all lie on a continuous and shallow
slope up Mount Improbable, with our eyes near a peak - not the
highest peak but a high one. In Climbing Mount Improbable, I
devoted a whole chapter each to the eye and the wing, demonstrating
how easy it was for them to evolve by slow (or even, maybe, not
all that slow) gradual degrees, and I will leave the subject here.
So, we have seen that eyes and wings are certainly not irreducibly
complex; but what is more interesting than these particular
examples is the general lesson we should draw. The fact that so
many people have been dead wrong over these obvious cases should
serve to warn us of other examples that are less obvious, such as the
cellular and biochemical cases now being touted by those
creationists who shelter under the politically expedient euphemism
of 'intelligent design theorists'.
We have a cautionary tale here, and it is telling us this: do not
just declare things to be irreducibly complex; the chances are that
you haven't looked carefully enough at the details, or thought carefully
enough about them. On the other hand, we on the science side
must not be too dogmatically confident. Maybe there is something
out there in nature that really does preclude, by its genuinely