Explaining the very improbable 17 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 light-sensitive cells (photo- cells')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 'elec- tronic 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 illus- trated 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 a result of this,some eyes are capable of detecting a single photon.The fastest and most sensitive film emulsions available to photographers need about 25 times as many photons in order to detect a point of light. The lozenge-shaped objects in the middle section of the cell are mostly mitochondria.Mitochondria are found not just in photocells,but in most other cells.Each one can be thought of as a chemical factory which,in the course of delivering its primary product of usable energy, processes more than 700 different chemical substances,in long,inter- weaving assembly-lines strung out along the surface of its intricately folded internal membranes.The round globule at the left of Figure I is the nucleus.Again,this is characteristic of all animal and plant cells. Each nucleus,as we shall see in Chapter 5,contains a digitally coded
Explaining the very improbable 17 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 light-sensitive 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 a result of this, some eyes are capable of detecting a single photon. The fastest and most sensitive film emulsions available to photographers need about 25 times as many photons in order to detect a point of light. The lozenge-shaped objects in the middle section of the cell are mostly mitochondria. Mitochondria are found not just in photocells, but in most other cells. Each one can be thought of as a chemical factory which, in the course of delivering its primary product of usable energy, processes more than 700 different chemical substances, in long, interweaving assembly-lines strung out along the surface of its intricately folded internal membranes. The round globule at the left of Figure 1 is the nucleus. Again, this is characteristic of all animal and plant cells. Each nucleus, as we shall see in Chapter 5, contains a digitally coded
18 The Blind Watchmaker database larger,in information content,than all 30 volumes of the Encyclopaedia Britannica put together.And this figure is for each cell, not all the cells of a body put together. The rod at the base of the picture is one single cell.The total number ofcells in the body (of a human)is about 10 trillion.When you eat a steak,you are shredding the equivalent of more than 100 billion copies of the Encyclopaedia Britannica
18 The Blind Watchmaker database larger, in information content, than all 30 volumes of the Encyclopaedia Britannica put together. And this figure is for each cell, not all the cells of a body put together. The rod at the base of the picture is one single cell. The total number of cells in the body (of a human) is about 10 trillion. When you eat a steak, you are shredding the equivalent of more than 100 billion copies of the Encyclopaedia Britannica
CHAPTER 2 GOOD DESIGN Natural selection is the blind watchmaker,blind because it does not see ahead,does not plan consequences,has no purpose in view.Yet the living results of natural selection overwhelmingly impress us with the appearance of design as if by a master watchmaker,impress us with the illusion of design and planning.The purpose of this book is to resolve this paradox to the satisfaction of the reader,and the purpose of this chapter is further to impress the reader with the power of the illusion of design.We shall look at a particular example and shall conclude that,when it comes to complexity and beauty of design, Paley hardly even began to state the case. We may say that a living body or organ is well designed if it has attributes that an intelligent and knowledgeable engineer might have built into it in order to achieve some sensible purpose,such as flying, swimming,seeing,eating,reproducing,or more generally promoting the survival and replication of the organism's genes.It is not necessary to suppose that the design of a body or organ is the best that an engineer could conceive of.Often the best that one engineer can do is, in any case,exceeded by the best that another engineer can do, especially another who lives later in the history of technology.But any engineer can recognize an object that has been designed,even poorly designed,for a purpose,and he can usually work out what that purpose is just by looking at the structure of the object.In Chapter I we bothered ourselves mostly with philosophical aspects.In this chapter,I shall develop a particular factual example that I believe would impress any engineer,namely sonar ('radar')in bats.In explaining each point,I shall begin by posing a problem that the living machine faces;then I shall consider possible solutions to the problem that a sensible 21
CHAPTER 2 GOOD DESIGN Natural selection is the blind watchmaker, blind because it does not see ahead, does not plan consequences, has no purpose in view. Yet the living results of natural selection overwhelmingly impress us with the appearance of design as if by a master watchmaker, impress us with the illusion of design and planning. The purpose of this book is to resolve this paradox to the satisfaction of the reader, and the purpose of this chapter is further to impress the reader with the power of the illusion of design. We shall look at a particular example and shall conclude that, when it comes to complexity and beauty of design, Paley hardly even began to state the case. We may say that a living body or organ is well designed if it has attributes that an intelligent and knowledgeable engineer might have built into it in order to achieve some sensible purpose, such as flying, swimming, seeing, eating, reproducing, or more generally promoting the survival and replication of the organism's genes. It is not necessary to suppose that the design of a body or organ is the best that an engineer could conceive of. Often the best that one engineer can do is, in any case, exceeded by the best that another engineer can do, especially another who lives later in the history of technology. But any engineer can recognize an object that has been designed, even poorly designed, for a purpose, and he can usually work out what that purpose is just by looking at the structure of the object. In Chapter 1 we bothered ourselves mostly with philosophical aspects. In this chapter, I shall develop a particular factual example that I believe would impress any engineer, namely sonar ('radar') in bats. In explaining each point, I shall begin by posing a problem that the living machine faces; then I shall consider possible solutions to the problem that a sensible 21
22 The Bli"d Watchmaker engineer might consider;I shall finally come to the solution that nature has actually adopted.This one example is,of course,just for illustration.Ifan engineer is impressed by bats,he will be impressed by countless other examples of living design. Bats have a problem:how to find their way around in the dark.They hunt at night,and cannot use light to help them find prey and avoid obstacles.You might say that if this is a problem it is a problem of their own making,a problem that they could avoid simply by changing their habits and hunting by day.But the daytime economy is already heavily exploited by other creatures such as birds.Given that there is a living to be made at night,and given that alternative daytime trades are thoroughly occupied,natural selection has favoured bats that make a go of the night-hunting trade.It is probable,by the way,that the nocturnal trades go way back in the ancestry of all us mammals.In the time when the dinosaurs dominated the daytime economy,our mammalian ancestors probably only managed to survive at all because they found ways of scraping a living at night.Only after the mysterious mass extinction of the dinosaurs about 65 million years ago were our ancestors able to emerge into the daylight in any substantial numbers. Returning to bats,they have an engineering problem:how to find their way and find their prey in the absence of light.Bats are not the only creatures to face this difficulty today.Obviously the night-flying insects that they prey on must find their way about somehow.Deep- sea fish and whales have little or no light by day or by night,because the sun's rays cannot penetrate far below the surface.Fish and dolphins that live in extremely muddy water cannot see because,although there is light,it is obstructed and scattered by the dirt in the water.Plenty of other modern animals make their living in conditions where seeing is difficult or impossible. Given the question of how to manoeuvre in the dark,what solutions might an engineer consider?The first one that might occur to him is to manufacture light,to use a lantern or a searchlight.Fireflies and some fish (usually with the help of bacteria)have the power to manufacture their own light,but the process seems to consume a large amount of energy.Fireflies use their light for attracting mates.This doesn't re- quire prohibitively much energy:a male's tiny pinprick can be seen by a female from some distance on a dark night,since her eyes are exposed directly to the light source itself.Using light to find one's own way around requires vastly more energy,since the eyes have to detect the tiny fraction of the light that bounces off each part of the scene.The light source must therefore be immensely brighter if it is to be used as a headlight to illuminate the path,than if it is to be used as a signal to
22 The Bli"d Watchmaker engineer might consider; I shall finally come to the solution that nature has actually adopted. This one example is, of course, just for illustration. If an engineer is impressed by bats, he will be impressed by countless other examples of living design. Bats have a problem: how to find their way around in the dark. They hunt at night, and cannot use light to help them find prey and avoid obstacles. You might say that if this is a problem it is a problem of their own making, a problem that they could avoid simply by changing their habits and hunting by day. But the daytime economy is already heavily exploited by other creatures such as birds. Given that there is a living to be made at night, and given that alternative daytime trades are thoroughly occupied, natural selection has favoured bats that make a go of the night-hunting trade. It is probable, by the way, that the nocturnal trades go way back in the ancestry of all us mammals. In the time when the dinosaurs dominated the daytime economy, our mammalian ancestors probably only managed to survive at all because they found ways of scraping a living at night. Only after the mysterious mass extinction of the dinosaurs about 65 million years ago were our ancestors able to emerge into the daylight in any substantial numbers. Returning to bats, they have an engineering problem: how to find their way and find their prey in the absence of light. Bats are not the only creatures to face this difficulty today. Obviously the night-flying insects that they prey on must find their way about somehow. Deepsea fish and whales have little or no light by day or by night, because the sun's rays cannot penetrate far below the surface. Fish and dolphins that live in extremely muddy water cannot see because, although there is light, it is obstructed and scattered by the dirt in the water. Plenty of other modern animals make their living in conditions where seeing is difficult or impossible. Given the question of how to manoeuvre in the dark, what solutions might an engineer consider? The first one that might occur to him is to manufacture light, to use a lantern or a searchlight. Fireflies and some fish (usually with the help of bacteria) have the power to manufacture their own light, but the process seems to consume a large amount of energy. Fireflies use their light for attracting mates. This doesn't require prohibitively much energy: a male's tiny pinprick can be seen by a female from some distance on a dark night, since her eyes are exposed directly to the light source itself. Using light to find one's own way around requires vastly more energy, since the eyes have to detect the tiny fraction of the light that bounces off each part of the scene. The light source must therefore be immensely brighter if it is to be used as a headlight to illuminate the path, than if it is to be used as a signal to