Chapter 4 Chapter Three

The reasons for creationism's enduring appeal are not hard to find.It's not that people believe every word of Genesis or other tribal origin stories to be true (at least most of the people I've met aren't), but that people discover for themselves the beauty and complexity of the living world and conclude that it's clearly long gone. Well designed.Some creationists recognize that Darwinian evolution offers at least one other alternative to their biblical teachings.To this end, they often resort to a slightly wiser objection, they deny the possibility of an evolutionary intermediate.They said: XX must have been designed by the Creator, because half XX is useless at all. The parts of XX were put together simultaneously; they could not have evolved step by step.For example, I happened to get a letter the day I started writing this chapter.The letter was from an American minister who was originally an atheist but had changed his mind after reading an article in National Geographic.Here is a passage from his letter: This article is about the amazing adaptation: Orchids adapt to their surroundings in order to reproduce successfully.

As I was reading this article, I was intrigued by the species' reproductive strategy.This ploy requires the cooperation of a drone.Apparently the flower is very similar to the female wasp, including a small hole in the right place to entice the male wasp to mate with the flower, just enough to reach the pollen in the flower.The male wasp then flies to the next flower to repeat the same process, thus completing cross-pollination.The first thing that attracts male wasps is the pheromone (a special chemical attractant that insects often use to attract mates) emitted by this flower.The flowers emit the exact same pheromones that the female wasp emits.I looked at the photos in this article carefully for a full minute with interest.So I realized with great shock that for this reproductive strategy to work, it had to be flawless from the start.It is impossible to achieve this step by step, for if the orchid does not look and smell like a female wasp, if it does not have a hole suitable for mating with a male wasp, or if the pollen in the hole does not sufficiently contact the reproductive organs of the male wasp , then the whole scheme cannot succeed at all.

I'll never forget the feeling of being on the brink of destruction.Because I suddenly realized that there must be some kind of God in some form, and must have an evolving relationship with the process of life formation.In short, the Creator God is not a pre-flood myth, but a real existence.Reluctantly, I felt immediately that I must try to learn more about this God. No doubt other people have turned to religion differently, but there are certainly many who have had similar experiences to this minister.They have seen or read about some of the wonders of nature. Oftentimes, this tends to fill them with awe, wonder, and even reverence for nature.What is more, like the above-mentioned writer, they decided that such specific natural phenomena as cobwebs, eagle eyes, or wings, or whatever, could not have evolved stepwise, because those intermediate, which only formed Half of the stages do nothing at all.The purpose of this chapter is to disprove the paradox that a complex device must be perfect in order to work.Orchids, by the way, were one of Darwin's favorite examples, and he devoted a book to the test of the principle of gradual evolution by natural selection in explaining the various designs orchids employ to attract insects to pollinate them.

At the heart of the minister's challenge was the assertion that, for the reproductive strategy to work, it had to be flawless from the start, and that there were no intermediate stages to get there.Regarding the evolution of the eye, the same problem can also be raised. In fact, such a problem has been raised frequently.I will return to this topic in this chapter. When I hear such assertions, I am often amazed at the confidence of the speakers.I would like to ask the minister, why are you so sure that the parts of the wasp-like orchid (or the eye, or whatever) must be perfect and in the right place from the beginning, otherwise it is useless?Did you actually think about it for a moment?Do you know exactly what happened to orchids (or wasps, or the eyes that wasps use to see females and orchids) in the first place?What makes you dare to assert that the wasp is so intractable that an orchid must resemble it in every respect?Think back to the last time you were fooled by a resemblance by chance.Perhaps you have doffed your hat to a stranger on the street, but you have mistaken her for an adult.Movie stars often use stuntmen to fall from horseback or jump off cliffs in their place.Often, the stuntman is only a resemblance to the real star, but fast action photography allows the stuntman to completely fool the audience.A picture in a magazine can arouse a man's sexual desire.A picture is nothing but ink on paper.It is only two-dimensional, not three-dimensional; the size of the picture is only a few tens of centimeters.It might even be just a caricature drawn with a few lines rather than a very photorealistic photo.Still, it can arouse a man's sexual desire.Presumably a fast-flying male sees only a glimpse of a female before attempting to mate with her.It pays attention to only a few key stimuli.

There are various reasons to think that wasps might be more gullible than people.This is the case with sticklebacks, which have bigger brains and better eyesight than wasps.Male sticklebacks have red bellies, and they intimidate not only other males, but even similar things with red bellies.My teacher, the Nobel Prize-winning behaviorist Nicole.Niko Tinbergen once told a famous story.A red mail truck passed by the window of his laboratory, and the red sticklebacks in the fish tank rushed to the side of the window, trying to intimidate the red mail truck.The belly of a mature female stickleback is full of fish eggs, and the bulging belly is very conspicuous.Tinbergen found that an extremely rough, slightly slender, silvery-white model, although it looks nothing like a stickleback to our eyes, has a bulging round belly, so the male sticklebacks are attracted to it. All mating moves.At the institute Tinbergen founded, some experiments have recently been done with so-called sex bombs.The sex bomb is a pear-shaped object, round and puffy, but not long.No matter how you look at it, no one would think of it as a fish.However, it is more effective at arousing the male fish's sexual desire.The stickleback sex bomb is a prime example of a super stimulant that is more effective than the real thing (female fish).One more example.Tinbergen published a photo of an oystercatcher trying to get on top of an egg the size of an ostrich egg.Birds have bigger brains and better eyesight than fishes, not to mention wasps.Still, the oystercatcher apparently decided that an egg the size of an ostrich egg would be the best thing to hatch.

Gulls, geese, and other ground-nesting birds have a constant response to eggs rolling out of the nest.They use the lower edge of their beaks to reach the egg outside the nest and poke it back into the nest.Tinbergen and his students found that gulls do this not only with their own eggs, but also with eggs laid by hens, and even logs or easy-open cans discarded by campers.Young herring gulls get food from their parents.They peck at a red spot on the parent's beak, stimulating the parent to regurgitate some fish from their bulging crops.Tinbergen and his colleagues showed that a simple cardboard model of the parent's head was very effective at eliciting begging behavior in young gulls.All that is really needed is a red dot.For juvenile herring gulls, their parents are the red dot.They may be able to see other parts of their parents' bodies, but that doesn't seem to matter.

This apparently limited vision is not limited to juvenile gulls.The head and face of adult black-headed gulls are black, which is very conspicuous.Tinbergen's student Robert.Robert Mash blackened wooden models of gull heads to study how important black faces are to other adult gulls.Each gull's head was nailed to the top of a wooden stick connected to an electric motor housed in a box.By remote control, Marsh can make the fake gull's head rise, fall and turn left and right.He buried the box near a gull's nest, with the wooden gull's head lowered under the sand, out of sight of the real gulls.After that, he came to a shelter near the gull nest every day to observe how the nest gulls reacted to the model wood gull head that rose and turned from side to side.The black-headed gull reacts to the wood-gull's head and the turning of the wood-gull's head as if it saw a real gull, although this is only a model on a stick, without a body, legs, wings, and tail, except mechanically, Except for lifting and turning lifelessly, it can neither make a sound nor move.It seems that for the black-headed gull, a disembodied black face is simply a terrible neighbor, whether it has a body, wings or other parts, it doesn't matter.

To get into hidden spots to observe the birds, Marsh took advantage of a long-known limitation of the bird's nervous system: Birds aren't born mathematicians.Generations of ornithologists have exploited this limitation.This is how they do it: Two people go into the bunker, and one of them leaves.If the trick wasn't played, the birds would have been wary of the cover, knowing that someone had entered it.However, if they see that one has left, they assume that both have left.If the bird cannot distinguish between a man and a man, is it still surprising that a male wasp can be deceived by an orchid that does not quite resemble a female wasp?In this regard, there is another story about the bird, but it is a tragic one.The mother turkey is a fierce guardian of her young.They must protect their children from predators such as weasels and carrion mice.The mother turkey's method of distinguishing intruders is as simple as it is shocking: attack anything that moves near her nest, unless it can make a sound like a baby turkey.This is the Austrian zoologist Wolfgang.Discovered by Wolfgang Schleidt.On one occasion, Schleter watched a mother turkey viciously kill all her offspring.The reason is simple and unfortunate: it's deaf.To the nervous system of a turkey, a predator is defined as a living object that cannot croak like a baby turkey.So while the baby turkeys not only looked like baby turkeys, acted like baby turkeys, and ran toward their mothers with the confidence of a baby turkey, they fell prey to their mother's strict definition of a predator.She killed them all to protect her children from their attack on her.

Among some insects, tragedies like those of turkeys also occur.There are some sensory cells on the bees' antennae that are only sensitive to oleic acid (a chemical) (they also have cells that are sensitive to other chemicals).Decomposing bee carcasses produce oleic acid, which stimulates the undertaker's action, which removes the dead body from the hive.The experimenter applied a drop of oleic acid to a live bee, and although the bee was clearly alive, it kicked its legs and struggled to be dragged out with the dead bees. Insect brains are much smaller than chicken or human brains.The eyes of insects, and even the large compound eyes of dragonflies, are much less acuity than those of humans or birds.Beyond that, we know that insect eyes see the world in a completely different way than ours.The great Austrian zoologist Karl.Feng.Karl von Frisch discovered in his youth that insects cannot see red light but can see ultraviolet light.Ultraviolet light is the unique color of insects, which we cannot see.The insect's eye is often attracted to the flapping of things, and flapping seems to partially replace what we call shape, at least for fast-flying insects.Male butterflies have been seen courting dead leaves that have fallen from trees.We see the female butterfly fluttering up and down with her large wings, and a male butterfly in flight sees her and courts her with great attention to the flutter.You can trick it with a strobe light.The strobe itself doesn't move, it just flashes on and off.If you get the frequency of the flashes right, the male butterfly will treat the strobe light like another butterfly that is flapping its wings at that frequency.Stripes, which appear to us as a static pattern, appear to a passing insect as something fluttering that can be imitated by a strobe light that flashes at the same frequency.The world seen by insects is so different from the world we see, that it is mere conjecture to speak of how perfectly orchids should imitate the female wasp, based on our own experience.

The wasp itself was the subject of a classic experiment.This experiment was originally carried out by the great French naturalist Jean.Henry.Fabre (Jean-Henri Fabre) did, and later repeated for many people, including members of the Tinbergen Institute.The female mud wasp returns to her earthen nest with prey paralyzed by her sting.It places its prey outside the earthen nest and burrows in by itself.Apparently it's to check to see if everything is ok inside.Then, it comes out again to drag the prey in.After the female wasp burrowed into the soil nest, the experimenters moved the prey a few inches from where it had been placed.When the wasp reappeared, it found its prey gone, but soon found it again.It then drags the prey to the nest entrance again.Only a few seconds had elapsed since it had inspected the interior of the hive.We see really no reason why it shouldn't take the next step of the routine of dragging the prey into the hive to complete the process.However, it has been reprogrammed to the previous step.It conscientiously and responsibly left the prey outside the entrance of the nest again, and re-entered to have a look.The experimenter can unabashedly repeat the game forty times until he tires himself; while the wasp behaves like a washing machine programmed at an early stage, unaware that the clothes have been washed. Washed forty times non-stop.Distinguished computer scientist Douglas.Douglas Hofstadter used two neologisms to describe this inflexible, mindless automaticity.So, at least in some respects, the wasps are pretty gullible.This is a completely different kind of dupe than the one Orchid has devised.

In any case, we must be wary of using human intuition to assert that in order for this reproductive strategy to work, it has to be flawless from the start.I may have done too well in convincing you that wasps are gullible.And you, may be doubting what I have said, and thinking exactly the opposite of the doubts of the letter writer I mentioned.If insects have such poor eyesight, and wasps are so gullible, why do orchids bother to make their flowers look like wasps?Wasps' eyesight wasn't always this bad.There are situations in which wasps have excellent eyesight: for example, when locating their nests after long foraging flights.Tinbergen observed the behavior of a bee-eating mud wasp (Philanthus).He waited for a wasp to fall into the hive.Before it re-emerged, Tinbergen quickly placed markers, such as twigs and pine cones, around the entrance to the hive.Then he took cover and waited for the wasp to fly out.After it came out, it flew around the hive two or three times, as if taking a picture of the spot in its head, and then flew off to look for food.Once it was far away, Tinbergen moved the twigs and pinecones a few feet away.When the wasp returned, it could not find its nest. It burrowed into the sand at the point corresponding to the new place for the twig and the pine-cone, and on the one hand the wasp was again deceived, but on the other hand its eyesight was this time respected by us.It appears that its previous orbital flight was indeed taking pictures in its head.It seems to recognize the figures of twigs and pine cones, or gestalts.Tinbergen tried many times, using different markers (pine cones in a circle, etc.), with the same result. Now we introduce Tinbergen's student Gerald.The experiment done by Gerard Baerends is in stark contrast to Fabre's washing machine experiment.Beirende used a species of mud wasp (Ammophila campestris) (Fabry also studied this mud wasp).This wasp is an unusually active food provider.Most wasps place food in their burrows, and after laying an egg, seal the burrow and let the larvae feed themselves. Ammophila is different.It is like a bird, returning to the burrow every day to check the growth of the larvae and provide food as needed.There's nothing particularly noteworthy about that.But the female bee always visits two or three holes at a time.One nest contains a relatively large, nearly mature larva; another, a small, newly hatched larva; and possibly a third, a larva of intermediate age and size .Naturally, the three larvae have different food requirements, and their mother provides food according to their respective circumstances.Through a series of laborious experiments, including swapping the larvae in the nests, Berende finally proved that mother bees do remember the different food requirements of each nest.It seemed clever, but Bernend also discovered that it wasn't smart either, and had its own very weird and distinctive stupidity.The first thing the mother bee does every morning is to inspect all her nests with larvae for a week.The mother bee determines its feeding behavior throughout the day based on the estimated situation when it patrols the nests at dawn.Beiren De's random frequent switching of larvae in each nest after the mother wasp's dawn inspection did not change the feeding behavior of the mother wasp.It seems that it only activates the nest assessment device during its early morning rounds, and then turns it off the rest of the time to conserve power. On the one hand, the story reminds us that in the mother bee's mind there are complex devices dedicated to counting, estimating, and even calculating.Now, it's easy to believe that the wasp's brain is really only fooled if the orchid is exactly like the female wasp in detail. But at the same time, the results of Beiren De's experiment also suggest that the wasps have the ability to be selectively blinded and deceived, which is exactly the same as the aforementioned washing machine experiment.This in turn led to the belief that a rough resemblance between orchids and female wasps would be just as effective.The general lesson we should learn is never to judge such things with human eyes.Don't say: I can't believe that so-and-so evolved by gradual selection; and if anyone says that, don't take it seriously.I call this fallacy the paranoid argument from the individual. What I am attacking is the idea that the gradual evolution of such-and-such cannot have happened, since such-and-such must obviously be perfect from the start for it to work.In answering this point of view so far I have drawn upon a great deal of fact that wasps and other animals see the world very differently from ours.In any case, it is easy for us to do stupid things.However, I have other, more persuasive and general arguments that need to be developed further.Let us use the word broken at the touch of a device, which must be perfect in order to be effective, as my writer asserted about the orchid that simulated the wasp.I find it really hard to imagine an unambiguous touch-and-break device, which makes sense.Airplanes don't break when touched.Because, although we would all prefer to entrust our lives to a Boeing 747 with all its parts in perfect working order, an airplane cannot survive the failure of a major component such as one or two engines. It's still able to fly.Microscopes are not broken at the first touch, because although a bad microscope can only provide blurry, gray images, it is much better to observe small objects with it than without a microscope.The radio is not broken at the first touch, if it is defective in some way, it may have lower fidelity, the sound will sound squeaky and distorted, but you will still be able to understand the meaning of the words.I stared out the window for ten minutes, trying to find a good example of even a man-made contraption that breaks at the touch of a finger, and I came up with only one: the arch.Arches have something of an almost destructive quality to them.That said, once the sides are closed, it has great strength and stability.But neither part can stand securely until it is closed.When building an arch, it must be supported with the help of brackets.The brackets act as a temporary support until the arch is completed; after they are built, the brackets can be removed, and the arch can stand firmly there for a long time. In the field of technology, we have no reason to say that a device should not be broken at the first touch in principle.Engineers have the power to design devices on their drawing boards.It's useless if it's only half done.Even in engineering, however, we'd be hard-pressed to find a contraption worthy of the name.I believe this statement is even more true for living devices.Let's take a look at the creationist propaganda in the biological world that breaks at the touch of a device.Wasps and orchids are just one example of the fascinating phenomenon of mimicry.A large number of animals and certain plants benefit from being like some other object (usually another animal or plant).Almost every aspect of life has something enhanced or disrupted by mimicry. Tigers and leopards are almost invisible as they stalk their prey in sun-dappled woodlands for their prey; the anchovy crouches on the bottom of the sea, their body surface closely resembles that of the ocean floor, and lures them with a long fishing rod The prey, there is a bait that looks like an earthworm on the head of the fishing rod; the slut firefly imitates the flashing pattern of another firefly during courtship, attracts the male firefly and eats it; Another type of fish that is hygienic will take a bite from the fin of a large fish once it has been allowed to approach it. To avoid being eaten, prey animals look like a variety of things, such as bark, twigs, bright green leaves, curly dead leaves, flowers, rose thorns, seaweed leaves, stones, guano, and the well-known poisonous animals. To lure predators away from their young, sandpipers and many other ground-nesting birds mimic the posture and gait of birds with broken wings. In order to protect her own eggs, the eggs of the cuckoo are similar to the eggs in the nest it deposits; the female fish of a mouth-breeding fish draws many false eggs on both sides to attract the male fish to suck the real eggs into the mouth for incubation. In all cases, one is tempted to think that the simulation has to be flawless.In the particular case of the wasp orchid, I enumerated the many perceptual deficits of wasps and other mimics.To be honest, orchids don't seem to me to be such a fantastic imitation of wasps, bees, or flies.To my eyes, leaf weeds imitate leaves much more accurately, probably because my eyes are more like the eyes of the predators (presumably birds) that leaf weeds are protecting against. The notion that imitation has to be perfect to be effective is also wrong in a more general sense.No matter how good a predator's eyesight may be, viewing conditions aren't always ideal.Furthermore, viewing conditions almost always range from very bad to very good on a continuum.Imagine an object that you are so familiar with that you can no longer mistake it for anything else.Or imagine a person, such as a close friend, with whom you are so close, so familiar, that you could never mistake her for someone else.But please imagine that she is coming towards you from far away.When you are very far away, you can't see her at all; when you are very close, you can see her facial features, every eyelash, and every pore.There will be no sudden transitions between the two. Recognizability is always progressively clear or gradually blurred.It is written in the infantry military drill: At two hundred yards, all parts of the body can be clearly seen; at three hundred yards, the outline of the face is indistinct; at four hundred yards, no face can be seen; At yards, the head is a point and the body is a cone.In the process of your friend getting closer to you, you will undoubtedly recognize her suddenly.But in this example, the probability of suddenly recognizing her decreases or increases with increasing or decreasing distance. In every sense, distance creates a gradual change in visibility.Fundamentally, visibility is graduated.Regardless of the degree of resemblance between the imitator and the prototype, whether they are very similar or not at all, there is a distance at which the eyes of the predator are deceived.Any closer than this distance and the predator's eyes are less likely to be fooled.Therefore, in the process of evolution, natural selection will tend to gradually improve the degree of similarity, which gradually reduces the critical distance for predators to be deceived.Here, instead of the eye to be deceived, I use the term the eye of the predator.In some cases, it will be the eyes of the prey, the eyes of the foster parents, the eyes of the female fish, etc. I have demonstrated this distance effect once when speaking to children.My colleague George at the Oxford University Museum.Dr. George McGavin made me a model of a forest.The model is dotted with twigs, fallen branches, dead leaves and moss.He cleverly arranged dozens of dead insects on the model, some of which (such as scarabs) were very conspicuous; Cockroaches are somewhere in between.I asked a few children from the audience to walk slowly towards my model, looking for insects in the model as they walked, and speaking out loud when they found one.When the children were far enough away from the models, even the most conspicuous insects were invisible to them.As they approached the model, they saw first the conspicuous insects, then those of moderate visibility (such as cockroaches), and finally those that were cleverly camouflaged.As for the best camouflaged insects, the children could not find them by staring at them at close range.When I showed them the insects, the children's mouths fell open in amazement. Distance is not the only variable factor that can be used to make this argument.Low light is another factor.In the middle of the night, when almost nothing is visible, a mere lookalike can fool inspection.At noon, only simulants that closely resemble each other can go unnoticed.Between these two moments, at dawn and dusk, in dim or overcast weather, in dense fog or downpours, there is a smooth and continuous change in visibility.Here again it occurs that natural selection tends towards similar degrees of gradual perfection.This is because, for any given degree of similarity, there must be a corresponding level of visibility.At this level of visibility, such a similarity would reveal differences from the prototype.Over the course of evolution, gradual improvements in similarity give organisms a survival advantage by brightening the critical light that tricks their enemies. Another similar gradient factor is the viewing angle.A camouflaged insect, whether it looks like it or not, will at some point be caught out of the corner of a predator's eye.At other times, it will be found under direct inspection.There must be a perspective in the periphery from which even the worst simulants can go undetected.There must also be a central perspective, at which even the best imitators are at risk.In between, there is a steady and continuous change in perspective.For any given level of analog accuracy, there is a critical angle at which a slight increase or decrease in similarity can make a big difference.In the process of evolution, the qualities that tend to be similar are steadily improved, because the critical angle of deceiving the enemy will become more and more positive. Enemy eyesight and intelligence can be considered another gradient factor.I mentioned this earlier in this chapter.For any given degree of resemblance between the simulated and the prototype, there may be one eye which is deceived by the simulated and another which is not.Still, evolution favors a steady increase in resemblance, as this tricks predators with more refined eyes.By saying this, I don't mean that predator eyes evolved in parallel with prey resemblance, although that could have happened.I mean, somewhere, there are predators with good eyesight and there are predators with poor eyesight, and all of those predators pose a threat.Low-level imitation can only fool predators with poor eyesight; high-level imitation can fool almost all predators.In between, too, there is a smooth and continuous transition. Speaking of bad eyesight versus good eyesight reminds me of a favorite mystery of the creationists.What's the use of half vision?How could natural selection favor imperfect eyes?I have dealt with this matter before, and enumerated a series of intermediate eyes, which actually exist in various phyla of animals.Here I'm going to combine the eyes with the protocol of the Gradient Doctrine that I've established.For tasks involving the eye, there is a continuous gradient.Right now, I'm using my eyes to identify characters displayed on a computer screen.To do this kind of thing, you need a pair of good vision and highly acuity eyes.I'm getting to the age where I can't read without reading glasses, but right now I'm still under-prescribed.As I get older, the prescription of the glasses I use will gradually deepen. I will find that without glasses, it will gradually become more and more difficult for me to see small objects that are close up.Here we have another kind of continuity, that is, the continuity of age. Any normal human being, no matter how old he is, has better eyesight than an insect.Some jobs can be performed by people with poor vision or even nearly blind.Your vision is blurry, but you can play a tennis ball, because the tennis ball is relatively large, and even if it is out of focus, you can see its position and movement clearly.Although jingflies have poor eyesight by our standards, dragonflies have good eyesight by insect standards; dragonflies can hunt insects in flight as easily as we hit a tennis ball.The eyes with poor vision can still take on the task of avoiding walking into a wall, slipping off a cliff, or unfortunately falling into the water.Even worse eyesight can detect a shadow passing overhead, which may be a cloud passing by, or a predator flying by.The extremely poor eyes can also tell day from night, which is also useful, among other things, to coordinate the breeding season and know when it's time to sleep.There is a chain of tasks that use the eye.For each eye, whether keen or poor, there is some sort of corresponding task, and a slight improvement in vision can make all the difference.It is not difficult to understand, therefore, that the eye develops gradually from a primitive, low early stage, through smooth and continuous intermediate transitions, to a degree of perfection, as we see the eye of the eagle or the eye of the youth. So what's the use of half-sightedness in a creationist's question?It's a light question, and a very easy one to answer.Half eyesight is exactly 1% better than forty-nine percent eyesight, which is already better than forty-eight percent eyesight, so the difference makes sense.Another problem that seems to weigh heavily is implicit in the statement that, as a physicist*, I simply cannot believe that there has been enough time for an organ as complex as the eye to evolve from nothing to where it is today.Do you really think you've had enough time?Both questions come from the argument of personal skepticism.The audience will naturally want an answer, but I still have to go back to the absolute value of geological time.If one step represents a century, then the entire epoch is shortened to a cricket throw.At this scale, if you want to go back to the origin of multicellular animals, you have to walk from New York to San Francisco. It can now be seen that trying to refute the claim that the geological age is not old enough is like smashing peanuts with a steam hammer.Trekking from coast to coast vividly expresses the time available for the evolution of the eye.However, by a pair of Swedish scientists Dan.Nielsen (Dan Nilsson) and Suzanne.New research by Susan ne Pelger suggests that just an absurdly small amount of that time is enough.By the way, when one speaks of eyes, one often means the eyes of vertebrates.然而在許多無脊椎動物中，適用的、能夠形成圖像的眼睛，已經各自獨立地、從頭開始進化了四十至六十次。在這四十次以上的獨立進化中，至少發現了九種有明顯區別的機理，包括針孔式眼睛，兩種照相機鏡頭式的眼睛、反射曲面（碟形衛星天線）式眼睛，以及好幾種複合眼。 尼爾森和皮爾格集中精力研究了照相機鏡頭式的眼睛，例如已經很發達的脊椎動物和章魚的眼睛。 你怎樣著手估計一定數量的進化變異所需要的時間呢？我們必須找到用於度量每一步進化規模的單位。用百分比變化來表示已到達的進化水準，是合情合理的。尼爾森和皮爾格採用一％作為單位來計量解剖學上量的變化。這只是一個方便的單位而已，就像焦被規定為完成一定數量的工作所需要的能量。當所有的變化都是發生在一維的時候，使用一％作為單位是最簡單的。以下面這種不大可能發生的情況為例：如果自然選擇傾向於極樂鳥的尾巴不斷變長，那麼這種鳥的尾巴從一米長進化成一千米長需要經過多少步呢？尾巴長度增加一％，不會引起粗心的觀察者的注意。然而，只需經過少得令人吃驚的步數就可以使尾巴進化到一千米長不到七百步。 尾巴從一米長進化到一千米長，這很好說（但是，卻非常荒謬），但是怎樣在相同的座標上為眼睛的進化定位呢？問題在於，對於眼睛來說，在許多不同的部位有許多不同的事情並行發生。尼爾森和皮爾格的任務，就是設計出眼睛進化的計算機模型來回答以下兩個問題。第一個問題我們在前幾頁中一次又一次地提出過，而他們利用電腦提出就更為系統化：從平整的表皮到完全的照相機式眼睛，是否存在平穩的漸進變化，即每一個中間類型都是一種改進？（自然選擇不能下山，即使在山谷那邊有一座誘人的更高的山峰，也不能走下坡路，這與人類設計者不同。）第二個問題，也就是我們在本節開始時提出的問題，完成這些必要的進化演變量需要多長的時間？尼爾森和皮爾格沒有試圖在電腦模型中類比細胞的內部工作情況。他們的工作是在創建了一個單個光敏細胞（把它稱為光電池也無妨）之後開始的。將來最好是再做一個電腦模型，從細胞內部的層次上展示第一個活的光電池是怎樣從一個最初期的、最普通的細胞一步步改進而來。然而，必須有個起點，而尼爾森和皮爾格的起點是在發明了光電池之後。他們是在組織水準上開始工作的：即，他們是在由細胞組成的組織這一水準，而不是在單個細胞水準進行工作。皮膚是一種組織，腸壁是組織，肌肉和肝臟也是組織。各種組織在隨機突變的影響下發生各種變化。一片片的組織可以變大，也可以變小，它們可能變厚或變薄。像晶體組織這樣的透明組織，它們能夠改變局部的折射率（即使光線彎折的能力）。 模擬眼睛比之模擬諸如獵豹飛奔的腿，其妙處就在於，利用基本的光學定律很容易測定其功效。眼睛用一個二維截面圖表示，電腦很容易以單個的實數算出它的視覺敏銳度或空間分辨能力。 用相應的數位形式表示獵豹的腿（或脊柱）的功效要難得多。尼爾森和皮爾格從一塊平展的視網膜開始，視網膜位於平展的色素層之上，在視網膜上又有一層起保護作用的透明層。透明層的折射率能夠產生局部隨機突變。然後，它們讓這個模型本身以隨機的方式變形，前題是任何變化必須是小變化，而且必須對前一個變化有改進。 結果很快就出來了，而且很明確。隨著視力敏銳程度的穩定提高，直接導致了以下的變化：開始時是平面結構，隨後變成淺淺的凹面，一直到不斷加深的杯狀體，眼睛模型本身的變形情況都在電腦螢幕上顯示出來。然後，人們又看到，透明層變厚，充滿了整個杯狀體，它的外表面均勻地膨凸，變成曲面。在這以後，幾乎像變魔術一樣，這透明填充物的一部分又濃縮成一個具有更高折射率的局部球形社區。該區的更高折射率並不是均勻的，而是呈梯度變化的，因此這個球形區是個卓越的分級折射率透鏡。對於製造透鏡的人來說，分級折射率透鏡是陌生的，但在生物的眼睛中卻很常見的。人類通過把玻璃磨成一定的形狀來製造透鏡。我們還製造複合透鏡，比如昂貴的照相機鏡頭。這種鏡頭包括若干個透鏡，但是每一個透鏡都是由均勻一致的玻璃製成的。與此相反，分級折射率透鏡卻具有連續變化的折射率。典型的情況下，越接近透鏡中心處，折射率越高。魚眼就是分級折射率透鏡。人們很早就知道，當焦距與半徑之比達到特定的理論最適值時，分級折射率透鏡就得到了畸變最小的效果。這個比值叫做馬希森比例（Mattiessen's ratio）。尼爾森和皮爾格的電腦模型與馬希森比例準確相符。 現在，讓我們看一看整個這一進化過程需要多長時間。為了回答這個問題，尼爾森和皮爾格必須對自然種群做一些遺傳上的假設。他們需要給模型提供一些合理的量值，如遺傳率。遺傳率用來表示變種受遺傳控制的程度。常用的測定遺傳率的方法，是將單卵孿生子（他們的遺傳物質完全相同）的相像程度與普通孿生子作比較。一項研究發現，在男人中，腿長的遺傳率為七十七％。遺傳率為一百％意味著什麼呢？你測量一位單卵孿生子的腿長，就可完全知道另一位單卵孿生子的腿長，即使他們是被分開來撫養也是一樣。 遺傳率為零％意味著，兩位單卵孿生子的腿長之間，與一定環境下特定人群中任何一個人相比，並無更大的相似程度。人類其他方面的遺傳率的測試結果為：頭寬九十五％；坐高八十五％；臂長八十％，身高七十九％。 遺傳率往往高於五十％。因此，尼爾森和皮爾格感到，給他們的眼睛模型設定遺傳率為五十％是穩妥的。這是一個保守的，或者說是一個悲觀的假設。與一個更接近實際的假設（比如七十％）相比，悲觀的假設會使估算出的眼睛進化所需時間更長些。他們情願自己的估計失之過長，因為像眼睛這樣的複雜器官，進化時間如果估計得過短，人們會從直覺上懷疑它的準確性。 出於同樣的原因，對於變異係數（即典型情況下，在群體中發生變異的機率）和選擇強度（即由於視力改進所造成的生存優勢的量值），他們都選取了保守的數值。他們甚至走得更遠，假設每個新一代每一次只在眼睛的一個部分發生改變；眼睛不同部分同時發生變化的情況也被排除，因為這會大大加速進化。然而，儘管採取了這些保守的假設，從平展表皮進化到魚眼所用的時間也很短：不到四十萬代。對於我們正在討論的小動物，可以假設每年一代，因此，進化到優良的照相機式眼睛所需時間不足五十萬年。 有了尼爾森和皮爾格的研究結果，在動物界中，眼睛已經有過不下四十次各自獨立的進化，也就不足為奇了。有足夠的時間供它在任一譜系之內從零開始連續進化一千五百次。給小動物設定了每一代的長度之後，眼睛進化所需時間，遠沒有人們輕易相信的那麼久，對於地質學家來說，它短得無法計量！在地質年代上，這只不過是個瞬間而已。 暗中為善。進化的一個主要特徵是它的漸進性。這是一個原則而非現實。進化過程的某些片斷可能發生，也可能不發生突然轉向。快速的進化可能會有間斷，甚至突然發生大突變，比如使孩子與其父母都不相像的重大變化。肯定還存在突然的物種滅絕這可能是由大的自然災害引起，比如彗星撞擊地球。發生這樣的事件之後，就會留下真空，有待快速發展的替補隊員來填補，就像哺乳動物取代了恐龍一樣。實際上，進化很可能並非總是漸進的。但是，在使用進化來解釋像眼睛這樣複雜的、顯然設定好的物體是怎樣成為現實時，它必須是漸進的。因為如果在這些情況下進化不是漸進的，它就完全失去了任何解釋力。在這些情況下，沒有了漸進性，我們就回到了魔法，而魔法與全無解釋是同義語。 眼睛，以及黃蜂授粉的蘭花給我們留下的印象是它們不可能發生。由於偶然的運氣它們自發組合的可能性，在現實世界中是很小的。一小步、一小步地逐漸進化，每一步都是幸運的，但又不是太幸運，這就是謎底。但是，如果它不是漸進的，它就不是謎底了，只是重述了一遍謎語而已。 有時人們會苦苦思索，這漸進的中間產物可能是什麼樣的？這些又將是對我們智慧的挑戰，但是，如果我們想像不出，那純粹是我們智力上的問題。這並不能證明沒有過漸進的中間產物。在思考漸進的中間產物方面，對我們智慧最大的挑戰之一，是蜜蜂那備受稱頌的舞蹈語言。這舞蹈語言是由著名的卡爾．Feng.弗里希的經典實驗工作發現的。在這裡進化的最終產物看起來是太複雜、太精巧了，它與我們平常料想得到的一隻昆蟲所能做的事相去太遠了，以致我們很難想像中間產物會是什麼樣子。 蜜蜂以一種仔細編碼的舞蹈為手段互相轉告哪裡有鮮花。如果它們所需要的食物距蜂巢很近，它們就跳圓形舞。這只是使其他蜜蜂興奮起來，爭先恐後地在蜂巢附近搜索。這不特別奇怪。非常奇特的事情發生在食物離蜂巢很遠的情況下。發現了食物的蜜蜂表演的舞蹈，我們稱為搖擺舞，用姿勢和時間長短告訴其他蜜蜂食物的方位和距離。搖擺舞是在蜂巢裡面，在蜂房的垂直面上表演的。由於蜂巢裡面很黑，其他蜜蜂看不見它跳舞。它們是感覺到、聽到的，因為跳舞的蜜蜂在表演時發出微弱的、有節奏的嗡嗡聲。 舞蹈路線呈8字形，中間有一段直行。直行線的指向蘊含一種巧妙的密碼，告訴其他蜜蜂食物的方向。 直行線並不直接指向食物的方向。它不可能這樣做，因為舞蹈是在蜂房的垂直面上表演，不管食物可能在什麼地方，蜂房本身的朝向是固定的。食物必須指出它的平面地理方位。垂直的蜂房更像釘在牆上的一幅地圖。畫在地圖上的直線，不直接指向一個特定的目的地，但是你可以依據約定的意思讀出它所指的方向。 為了弄清蜜蜂所遵循的約定，你必須首先知道蜜蜂像許多其他昆蟲一樣，飛行時將太陽作為指南針來導航。我們在航行時也採用類似的方法。這種方法有兩個缺點。第一，太陽常常躲在雲層裡。 蜜蜂是靠一種感官來解決這個問題的，而我們沒有這種感官。此外，馮．弗里希發現蜜蜂能看見光的偏振方向，因此即使看不見太陽，它們也知道太陽的位置。把太陽當做指南針存在的第二個問題是，隨著時間的推移，太陽在天空中移動。蜜蜂靠它的生物鐘解決這個問題。Feng.弗里希發現，幾乎令人難以置信的是，跳舞的那只蜜蜂在尋找食品遠征歸來之後，在蜂巢中被關了數小時後，它們會慢慢改變其直行線的方向，就好像這條線是二十四小時制時鐘的時針一樣。它們在蜂巢內看不見太陽，卻慢慢地轉動著跳舞的方向以跟上太陽的運動，這是生物鐘告訴它們外面正在進行著的事情。 令人驚奇的是，從南半球來的各種蜜蜂也會做同樣的事，不過方向相反，正如它們在南半球應做的那樣。 現在讓我們來看看舞蹈密碼本身。舞蹈的直行線垂直向上，表示食物在朝著太陽的方向。垂直向下，表示食物在背著太陽的方向。介於兩者之間的角度都代表相應的方向。向上偏左五十度，表示在水平面上從太陽方向左偏五十度。但是在實際舞蹈中並沒有如此精確的角度。why is that?因為把羅盤分成三百六十度是人為的規定，而蜜蜂則將羅盤大約分成八個蜜蜂度。實際上，除了職業航海家外，我們的做法也差不多。我們把非正式的羅盤分成八個區：北、東北、東、東南、南、西南、西、西北。 在蜜蜂的舞蹈裡也含有食物距離的密碼。或者說，舞蹈的各方面情況旋轉速率、搖擺速率、嗡嗡叫的速率都與食物的距離有關，任何一個方面，或者幾個方面相組合，都能被其他蜜蜂用來讀出食物的距離。離食物越近，舞就跳得越快。通過聯想，你就能記住這一點：與一隻在遠處找到食物的蜜蜂相比，一隻蜜蜂發現了離蜂巢很近的食物會更興奮，體力消耗也少。我們將會看到，這還暗示了舞蹈是怎樣進化的。 總而言之，一隻尋食的蜜蜂發現了一處很好的食源。它滿載著花蜜和花粉飛回蜂巢，把花蜜和花粉交給迎接它的工蜂，然後就開始跳舞。在蜂房的垂直面的某一點（隨便哪一點）上，它開始快速地繞8字形跳舞。其他工蜂聚集在它周圍，感覺著、傾聽著。它們數著嗡嗡聲的速率，或許還數著旋轉的速率。當舞蹈者搖擺它的腹部的時候，其他蜜蜂度量著它的直行線與垂線之間的夾角。然後它們來到蜂巢門口，從黑暗中來到陽光下。它們觀察太陽的位置不是觀察太陽的高度角，而是觀察太陽在水平面上的方位角。然後，它們沿著一條直線飛去，直線與太陽的夾角，等於找到食物的蜜蜂跳舞時的方向與垂線的夾角。它們沿著這個方向一直飛，飛的距離與跳舞時發出的嗡嗡聲的速率的對數成反比。有趣的是，如果原來那只蜜蜂為了尋找食物而飛了彎路的話，它向同伴們指引的方向，不是它所飛過的彎路，而是調整過的直接飛向食物的方向。 蜜蜂跳舞的故事令人難以置信，也確有人不相信。我將在下一章回到懷疑者，回到最近的一些實驗上來，這些實驗結果終於印證了這事。在這一章，我想討論一下蜜蜂的舞蹈是如何逐漸進化來的。在進化過程的中間階段這些舞蹈看起來是什麼樣的？當這種舞蹈尚不完善時它們又是如何起作用的？順便說一句，敘述這些問題的詞語並不十分準確。沒有什麼生物能在不完善的中間階段生存。古代的、已經死去很久的蜜蜂，從事後認識，它們的舞蹈可以被看作是走向現代蜜蜂舞蹈的中間階段。而那些蜜蜂也曾經生活得很好。它們走完了蜜蜂的全部生命歷程，從未想到它們正在走向某種更好的生活。再者，現代的蜜蜂舞蹈也許並不是最後的產物，而且可能在我們和我們的蜜蜂都死後，進化成更令人驚奇的東西。不管怎麼說，現代的蜜蜂舞蹈是怎樣逐步進化來的，對我們來說確實是個謎。這些逐漸發展的中間類型看起來是什麼樣，又是怎麼起作用的呢？Feng.弗里希自己也注意到了這個問題。他是通過考察家族樹、研究蜜蜂的現代遠親來處理這個問題的。這些現代遠親並不是蜜蜂的祖先，因為它們與現在的蜜蜂生活在同一時代。但是它們也許保留著蜜蜂祖先的特徵。蜜蜂是溫帶昆蟲，它們在中空的樹幹裡或洞穴裡築巢。它們最近的親戚是熱帶蜂。熱帶蜂能在露天裡做巢，即把巢做在樹枝上或裸露的岩石上。因此，它們在跳舞時能看到太陽，而不必求助於用垂線代表太陽方向這種規定。太陽能代表它自己。 蜜蜂的一種熱帶親戚小蜜蜂（apis florea）在蜂巢頂端的水平面上跳舞。在舞蹈中，它們的直行線直接指向食物。這裡不需要地圖上的那種規定，直接指出方向就行了。當然，這似乎是蜜蜂進化道路上的一個可能的過渡階段，但是我們還是想瞭解在它之前、之後的一些中間階段。矮蜂舞的先驅會是什麼呢？為什麼剛找到食物的蜜蜂必須一圈又一圈地繞8字形飛舞，而其直線的方向直接指向食物呢？有人認為，這是起飛時一種儀式化了的形式。Feng.弗里希認為，在舞蹈進化之前，找到食物的蜜蜂飛回蜂房，卸掉負載之後，會直接向著原來的方向起飛，再次飛回那食源地。 為了準備起飛，它將頭朝向正確的方向，還會向前走上幾步。如果故意誇大或延長起飛時的助跑動作能發動其他蜜蜂跟隨其後，那麼，自然選擇就會促使這種趨勢進一步發展。也許這種舞蹈就是一種儀式化的反反覆覆的起飛助跑動作。這似乎是可能的，因為不管它們是不是利用舞蹈，蜜蜂時常採用一隻跟著一隻地飛向食物源的這種直接策略。另外一個事實也使這種想法具有可能性，即：跳舞的蜜蜂微微張開翅膀，好像是準備起飛，然後它們振動翅膀肌肉，這種振動雖不足以使蜜蜂起飛，卻可以發出聲音，這聲音也就成了舞蹈信號的一個重要的組成部分。 一種顯而易見的延長和誇大助跑動作的方式，就是重複這些動作。重複，就意味著回到起點，然後再朝食物的方向走幾步。回到起點有兩種方式，即：可以在跑道的盡頭向右轉或者向左轉。如果你總是向左轉或總是向右轉，那麼，哪個方向是真正的起飛方向，而哪個方向是重新回到跑道起點的方向就不明確了。消除這種糊塗的最佳辦法，就是左轉右轉交替使用。這就是自然選擇的8字形。 但是，食物距離與舞蹈速率之間的關係是怎樣演化的呢？如果舞蹈速率與食物距離成正比關係，這種關係就很難解釋。但是，你會記得，實際上這種關係正相反：食物越近，舞得越快。這直接暗示著逐步進化的一條可能途徑。在舞蹈本身開始進化之前，尋找食物的蜜蜂也許只是儀式化地反覆表演起飛助跑動作，也沒有特定的速率。至於跳舞的速率，也許是它們偶然覺得喜歡那麼跳。試想，如果你剛從幾英裡以外飛回家，滿載著花蜜和花粉，難道你還願意飛速地繞著蜂房衝來衝去麼？不能，你一定已經感到精疲力竭了。 如果你剛剛在離蜂巢很近的地方發現了一處豐饒的食物源，經過很短的歸途你仍然會精神飽滿、體力充沛。於是，人們就不難理解，食物的距離和舞蹈的速率之間，怎樣從最初的偶然聯繫發展成儀式化的、正式而可靠的密碼。 現在讓我們看一看最有爭議的中間階段。直行路線直接指向食物的原始舞蹈怎樣轉變為另一種舞蹈，用與垂線之間的夾角來表示食物與太陽之間的夾角？這個轉變勢在必行，部分是因為蜂巢裡面很暗，從那裡看不見太陽；部分則因為在蜂房的垂直面上跳舞時不可能直接指向食物，除非垂直面本身碰巧朝向食物。但是這還不足以說明這種轉變必定會發生。我們還必須解釋清楚，這個困難的轉變是怎樣經過一系列可能的步驟，一步一步實現的。 這看上去很難解釋，但是關於昆蟲神經系統的一個奇特事實可以幫我們的忙。下面是一個曾經對各種昆蟲從甲蟲到螞蟻都做過的一個非同尋常的實驗。實驗開始時，讓一隻甲蟲在水準放置的木板上行走，有一隻電燈照著它。第一件要證明的事是，這只甲蟲在利用光羅盤來導向。將燈泡的位置改變一下，甲蟲便相應地改變它行進的方向。如果它行進的方向與光源成三十度角，改變燈泡位置後，它會改變自己的走向，使之仍與移動了的光源成三十度角。實際上，你可以把光束當做舵柄，來引導甲蟲到你想讓它去的任何地方。關於昆蟲的這個事實很早就為人所知了：它們以太陽（或者月亮，或者星星）作為指南針。你用一個燈泡就很容易使它們上當受騙。談到這裡，一切都順當。現在讓我們看一個有趣的實驗。將燈熄滅，同時把木板豎起來。這甲蟲繼續無所畏懼地行進，並且，說也奇怪，它改變了行進方向，使行進方向與垂線之間的夾角跟原先與光線之間的夾角相同在我們的例子裡是三十度。 沒有人知道為什麼會發生這樣的事情，但它確實發生了。這好似洩漏了昆蟲神經系統一個偶發的現象種感覺上的混亂，重力感覺與視覺感覺線路的交錯，有點像我們被當頭打了一棒時，眼前看見金星閃爍。不論怎樣，這大概為解釋蜜蜂舞的垂線代表太陽密碼的演化，提供了必要的橋樑。 發人深省的是，如果你在蜂巢裡點上一盞電燈，蜜蜂就會拋開它們的重力感，用燈光的方向直接代替它們密碼中的太陽。這一早就知曉的事實被用於一個聰明巧妙的實驗中，最終證明了蜜蜂的舞蹈確實起作用。在下一章中我還將討論這個問題。同時，我們已經發現了一系列可能的逐漸發展的中間類型，現代的蜜蜂舞蹈就是經過這些中間類型從簡單的初始階段進化來的。上面講的，如我所述，是以馮．弗里希的想法為基礎的。這想法實際上可能不一定正確。然而，與之多少有些相似的事情確曾發生過。我講這個故事是為了回答自然懷疑論，即來自個人懷疑論的質難。當人們面對精妙的或複雜的自然現象時，就會萌生這種論調。懷疑論者說：我不能想像有一系列可能的中間類型，因此，沒有這樣的中間階段。這種現象是一種自發產生的奇蹟。Feng.弗里希已經提供了一個可能的中間類型系列，即便它不是一個完全正確的系列，但它是可能的這一事實本身就足以挫敗個人懷疑論的質難。我們迄今討論過的其他例子（從模擬黃蜂的蘭花到照相機式眼睛）也是這樣。 自然界中一切難以理解和令人困惑的現象都會被懷疑達爾文漸進的進化論的人搜集起來。比如，有人曾要求我解釋，在太平洋海溝中既無光線、水壓又可能超過一千個大氣壓的環境裡，生物是怎樣逐漸進化的。在太平洋海溝深處沸熱的火山口周圍，生長著一個完整的動物群落。細菌的生化過程全然不同，它們利用火山口的熱進行硫的代謝而不是氧的代謝。較大動物群落的生存最終都依賴於這些硫細菌，正如普通生命依賴於從太陽獲取能量的綠色植物。 硫群落中的動物全都是在其他地方發現的普通動物的親戚。 它們是怎樣進化的？通過了什麼樣的中間階段？爭論的形式完全一樣。為了進行解釋，我們需要的只是至少一個自然梯度，而當我們潛入海中時，梯度是十分豐富的。一千個大氣壓是一個可怕的壓力，但它在數量上僅僅比九百九十九個大氣壓多了一個大氣壓而已，而九百九十九個大氣壓也僅比九百九十八個大氣壓多了一個大氣壓而已，等等，等等。海底提供了從零經過所有中間深度，一直到一萬米的深度梯度；壓力則從一個大氣壓平緩地增加到一千個大氣壓；亮度也從水面處明亮的白晝緩緩地變為深海的完全黑暗，只有魚類的發光器官裡的少量發光菌能提供一點光亮。沒有明顯的突然中斷現象。 對於業已適應的每一壓力與黑暗程度，都會存在一種特定的動物，它與那些生存在更深一噚、更暗一流明的地方的動物略有不同。對於每一但是這一章已經太長了。你知道我的方法，華生。應用它們吧。 原注：我希望這不至於失禮。為了支持我的觀點，我從《科學與基督教信仰》一書中摘錄了一段話。作者，傑出的物理學家約翰。波爾金霍恩（John Polkinghorne）牧師稱：有的人，像理查．道金斯（Richard Dawkins），可以向人們展示具有說服力的生動描述，說明一些很小的差異如何經過篩選和積累而發展形成大的差別。但是，出於本能，一個物理學家卻願看到這樣的估計，不管它多麼粗略，即：從一個對光略有敏感的細胞，進化成一個完全成形的昆蟲眼睛需要經過多少步驟，以及發生這些必要的突變大約需要經過多少代。