Read The Blind Watchmaker for Free Online

aware that my characterization of a complex object - statistically improbable in a direction that is specified not with hindsight - may seem idiosyncratic. So, too, may seem my characterization of physics as the study of simplicity. If you prefer some other way of defining complexity, I don’t care and I would be happy to go along with your definition for the sake of discussion. But what I do care about is that, whatever we choose to call the quality of being statistically improbable in a direction specified without hindsight, itisan important quality that needs a special effort of explanation. It is the quality that characterizes biological objects as opposed to the objects of physics. The kind of explanation we come up with must not contradict the laws of physics. Indeed it will make use of the laws of physics, and nothing more than the laws of physics. But it will deploy the laws of physics in a special way that is not ordinarily discussed in physics textbooks. That special way is Darwin’s way. I shall introduce its fundamental essence in Chapter 3 under the title of cumulative selection .
    Meanwhile I want to follow Paley in emphasizing the magnitude of the problem that our explanation faces, the sheer hugeness of biological complexity and the beauty and elegance of biological design.
    Chapter 2 is an extended discussion of a particular example, ‘radar’ in bats, discovered long after Paley’s time. And here, in this chapter, I have placed an illustration (Figure 1) how Paley would have loved the electron microscope! - of an eye together with two successive ‘ zoomings in’ on detailed portions. At the top of the figure is a section through an eye itself. This level of magnification shows the eye as an optical instrument. The resemblance to a camera is obvious. The iris diaphragm is responsible for constantly varying the aperture, the stop.
    The lens, which is really only part of a compound lens system, is responsible for the variable part of the focusing. Focus is changed by squeezing the lens with muscles (or in chameleons by moving the lens forwards or backwards, as in a man-made camera). The image falls on the retina at the back, where it excites photocells.
    The middle part of Figure 1 shows a small section of the retina enlarged. Light comes from the left. The lightsensitive cells (‘ photocells’) are not the first thing the light hits, but they are buried inside and facing away from the light. This odd feature is mentioned again later. The first thing the light hits is, in fact, the layer of ganglion cells which constitute the ‘electronic interface’ between the photocells and the brain. Actually the ganglion cells are responsible for preprocessing the information in sophisticated ways before relaying it to the brain, and in some ways the word ‘interface’ doesn’t do justice to this. ‘Satellite computer’ might be a fairer name. Wires from the ganglion cells run along the surface of the retina to the ‘blind spot’, where they dive through the retina to form the main trunk cable to the brain, the optic nerve. There are about three million ganglion cells in the ‘ electronic interface’, gathering data from about 125 million photocells.
    At the bottom of the figure is one enlarged photocell, a rod. As you look at the fine architecture of this cell, keep in mind the fact that all that complexity is repeated 125 million times in each retina. And comparable complexity is repeated trillions of times elsewhere in the body as a whole. The figure of 125 million photocells is about 5,000 times the number of separately resolvable points in a good-quality magazine photograph. The folded membranes on the right of the illustrated photocell are the actual light-gathering structures. Their layered form increases the photocell’s efficiency in capturing photons, the fundamental particles of which light is made. If a photon is not caught by the first membrane, it may be caught by the second, and so on. As