The Greatest Show on Earth

Many flowers use a bribe of food, usually nectar. Maybe bribe is too loaded a word. Would you prefer 'payment for services rendered'?

Insects have good colour vision, but their whole spectrum is shifted towards the ultraviolet and away from the red. Like us, they see yellow, green, blue and violet. Unlike us, however, they also see well into the ultraviolet range; and they don't see red, at 'our' end of the spectrum. If you have a red tubular flower in your garden it is a good bet, though not a certain prediction, that in the wild it is pollinated not by insects but by birds, who see well at the red end of the spectrum - perhaps hummingbirds if it is a New World plant, or sunbirds if an Old World plant. (Page 51)

From a moth's point of view, flowers that reliably provide nectar are like docile, productive milch cows. From the flowers' point of view, moths that reliably transport their pollen to other flowers of the same species are like a well-paid Federal Express service, or like welltrained homing pigeons. (Page 52)

is a fortunate coincidence that the fragrances that bees and butterflies prefer happen to appeal to us too. (Page 53)

I have implied that insects breed flowers for high nectar yield, like dairymen breeding massively uddered Friesians. But it is in the flowers interests to ration their nectar. Satiate an insect and it has no incentive to go on and look for a second flower - bad news for the first flower, for which the second visit, the pollinating visit, is the whole point of the exercise. From the flowers' point of view, a delicate balance must be struck between providing too much nectar (no visit to a second flower) and too little (no incentive to visit the first flower). (Page 53)

1 Humans deliberately choose attractive roses, sunflowers etc. for breeding, thereby preserving the genes that produce the attractive features. This is called artificial selection, it's something humans have known about since long before Darwin, and everybody understands that it is powerful enough to turn wolves into chihuahuas and to stretch maize cobs from inches to feet.

it was Darwin who first spotted that you don't have to have a choosing agent. The choice can be made automatically by survival - or failure to survive. Survival counts, Darwin realized, because only survivors reproduce and pass on the genes (Darwin didn't use the word) that helped them to survive. (Page 62)

4 Without any kind of choosing agent, those individuals that are 'chosen' by the fact that they happen to possess superior equipment to survive are the most likely to reproduce, and therefore to pass on the genes for possessing superior equipment. Therefore every gene pool, in every species, tends to become filled with genes for making superior equipment for survival and reproduction. (Page 63)

'church clocks fallacy'. The clocks in the towers of two neighbouring churches chime the hours, but St A's a little before St B's. A Martian visitor, noting this, might infer that St A's chime caused St B's to chime. We, of course, know better, but the only real test of the hypothesis would be experimentally to ring the St A's chime at random times rather than once per hour. The Martian's prediction (which would of course be disproved in this case) is that St B's clock will still chime immediately after St A's. It is only experimental manipulation that can determine whether an observed correlation truly indicates causation. (Page 66)

Perfection in one department must be bought, in the form of a sacrifice in another department. (Page 70)

A body is a patchwork of compromises. (Page 70)

What happens under domestication is that animals are artificially shielded from many of the risks that shorten the lives of wild animals.

Raymond Coppinger. The idea is that the evolution of the dog was not just a matter of artificial selection. It was at least as much a case of wolves adapting to the ways of man by natural selection. Much of the initial domestication of the dog was selfdomestication, mediated by natural, not artificial, selection. Long before we got our hands on the chisels in the artificial selection toolbox, natural selection had already sculpted wolves into self-domesticated 'village dogs' without any human intervention.

Coppinger's view, the first step in the domestication of the dog, and it was achieved by natural selection, not artificial selection.

They recognize a widespread phenomenon called 'pleiotropy', whereby genes have more than one effect, seemingly unconnected.

Insects have compound eyes, which are not so acute as our camera eyes, and the shapes and colours of insect-mimicking orchids, reinforced by seductive scents that mimic those of female insects, are more than capable of tricking males. By the way, it is quite probable that the mimicry is enhanced when seen in the ultraviolet range, from which we are cut off. (Page 77)

The intimate relationship between flowers and their pollinators is a lovely example of what is called co-evolution - evolution together.

The measured age of our planet is about 4.6 billion years, or about 46 million centuries. The time that has elapsed since the common ancestor of all today's mammals walked the Earth is about two million centuries. A century seems a pretty long time to us. Can you imagine two million centuries, laid end to end? The time that has elapsed since our fish ancestors crawled out of the water on to the land is about three and a half million centuries: that is to say, about twenty thousand times as long as it took to make all the different - really very different breeds of dogs from the common ancestor that they all share. (Page 81)

If the history-deniers who doubt the fact of evolution are ignorant of biology, those who think the world began less than ten thousand years ago are worse than ignorant, they are deluded to the point of perversity. They are denying not only the facts of biology but those of physics, geology, cosmology, archaeology, history and chemistry as well. (Page 85)

Man-made clocks work on timescales that are very short by evolutionary standards - hours, minutes, seconds and the timedependent processes they use are fast: the swinging of a pendulum, the swivelling of a hairspring, the oscillation of a crystal, the burning of a candle, the draining of a water vessel or an hourglass, the rotation of the earth (registered by a sundial). All clocks exploit some process that occurs at a steady and known rate. A pendulum swings at a very constant rate, which depends upon its length but not, at least in theory, on the amplitude of the swing or the mass of the bob on the end.

Our evolutionary clock needs to be zeroed at some point, so that we can calculate the elapsed time since a starting point, to give us, for example, the absolute age of some object such as a rock. Radioactive clocks for dating igneous (volcanic) rocks are conveniently zeroed at the moment the rock is formed by the solidification of molten lava. (Page 87)

This fast end of the spectrum of natural clockstree rings and carbon dating - is useful for archaeological purposes, and for dating specimens on the sort of timescale that covers the domestication of the dog or the cabbage. At the other end of the scale, we need natural clocks that can time hundreds of millions, even billions, of years. And, praise be, nature has provided us with just the wide range of clocks that we need. What's more, their ranges of sensitivity overlap with each other, so we can use them as checks on each other. (Page 87)

Dendrochronologists measure rings on recent trees, where the exact date of every ring is known by counting backwards from the year in which the tree is known to have been felled. From these measurements, they construct a reference collection of ring patterns, to which you can compare the ring patterns of an archaeological sample of wood whose date you want to know. So you might get the report: 'This Tudor beam contains a signature sequence of rings that matches a sequence from the reference collection, which is known to have been laid down in the years 1541 to 1547. The house was therefore built after AD 1547'. (Page 89)

To understand how radioactive clocks work, we first need to understand what is meant by a radioactive isotope. All matter is made up of elements, which are usually chemically combined with other elements. There are about 100 elements, slightly more if you count elements that are only ever detected in laboratories, slightly fewer if you count only those elements that are found in nature. Examples of elements are carbon, iron, nitrogen, aluminium, magnesium, fluorine, argon, chlorine, sodium, uranium, lead, oxygen, potassium and tin. The atomic theory, which I think everybody accepts, even creationists, tells us that each element has its own characteristic atom, which is the smallest particle into which you can divide an element without it ceasing to be that element. What does an atom look like, say an atom of lead, or copper, or carbon? Well, it certainly looks nothing like lead or copper or carbon. It doesn't look like anything, because it is too small to form any kind of image on your retina, even with an ultra-powerful microscope. We can use analogies or models to help us visualize an atom. The most famous model was proposed by the great Danish physicist Niels Bohr. The Bohr model, which is now rather out of date, is a miniature solar system. The role of the sun is played by the nucleus, and around it orbit the electrons, which play the role of planets. As with the solar system, almost all the mass of the atom is contained in the nucleus (sun'), and almost all the volume is contained in the empty space that separates the electrons ('planets)

Chemistry is a dance of electrons. It is all about the interactions of atoms via their electrons. Chemical bonds are easily broken and remade, because only electrons are detached or exchanged in chemical reactions. The forces of attraction within atomic nuclei are much harder to break. That's why 'splitting the atom' has such a menacing ring to it but it can happen, in 'nuclear'

The predictability of the rate of decay is the key to all radiometric clocks. Another word for unstable' is 'radioactive. (Page 94)

Every unstable or radioactive isotope decays at its own characteristic rate which is precisely known. (Page 95)

The favoured measure of decay rate is the halflife. The half-life of a radioactive isotope is the time taken for half of its atoms to decay. The half-life is the same, no matter how many atoms have already decayed - that is what exponential decay means. (Page 95)

isotope much used on the evolutionary timescale is potassium-40, with its half-life of 1.26 billion years, and I'm going to use it as my example, to explain the whole idea of a radioactive clock. It is often called the potassium argon clock, because argon-40 (one lower in the periodic table) is one of the elements to which potassium40 decays (the other, resulting from a different kind of radioactive decay, is calcium-40, one higher in the periodic table). (Page 96)

Like all the radioactive clocks used by geologists, potassium/ argon timing works only with so-called igneous rocks. Named after the Latin for fire, igneous rocks are solidified from molten rock - underground magma in the case of granite, lava from volcanoes in the case of basalt. When molten rock solidifies to form granite or basalt, it does so in the form of crystals. These are normally not big, transparent crystals like those of quartz, but crystals that are too small to look like crystals to the naked eye. The crystals are of various types, and several of these, such as some micas, contain potassium atoms. Among these are atoms of the radioactive isotope potassium40. When a crystal is newly formed, at the moment when molten rock solidifies, there is potassium-40 but no argon. The clock is 'zeroed' in the sense that there are no argon atoms in the crystal. (Page 96)

Only igneous rocks provide radioactive clocks, but fossils are almost never found in igneous rock. Fossils are formed in sedimentary rocks like limestone and sandstone, which are not solidified lava. They are layers of mud or silt or sand, gradually laid down on the floor of a sea or lake or estuary. The sand or mud becomes compacted over the ages and hardens as rock. Corpses that are trapped in the mud have a chance of fossilizing. Even though only a small proportion of corpses actually do fossilize, sedimentary rocks are the only rocks that contain any fossils worth speaking of. (Page 97)

Sedimentary rocks unfortunately cannot be dated by radioactivity (Page 97)

Of all the elements, carbon is the one that seems most indispensable to life-the one without which life on any planet is hardest to envisage.

All living creatures, whether plants or animals, have approximately the same ratio of carbon-12 to carbon14, which is the same ratio as you'll find in the atmosphere. (Page 104)

So, when is the clock zeroed? At the moment when a living creature, whether animal or plant, dies. At that moment, it is severed from the food chain, and detached from the inflow of fresh carbon-14, via plants, from the atmosphere. As the centuries go by, the carbon14 in the corpse, or lump of wood, or piece of cloth, or whatever it is, steadily decays to nitrogen-14. The ratio of carbon-14 to carbon-12 in the specimen therefore gradually drops further and further below the standard ratio that living creatures share with the atmosphere.

Carbon dating is a comparatively recent invention, going back only to the 1940s. In its early years, substantial quantities of organic material were needed for the dating procedure. Then, in the 1970s, a technique called mass spectrometry was adapted to carbon dating, with the result that only a tiny quantity of organic material is now needed. This has revolutionized archaeological dating. The most celebrated example is the Shroud of Turin. (Page 105)

I have repeatedly emphasized that there are lots of different clocks that the modern evolutionary detective can use, and also that ther work best on different, but overlapping timescales. Radioactive clock can be used to give independent estimates of the age of one piece of rock, bearing in mind that all the clocks were zeroed simultaneously when this very same piece of rock solidified. When such comparisons have been made, the different clocks agree with each other - within the expected margins of error. This gives great confidence in the correctness of the clocks. Thus mutually calibrated and verified on known rocks, these clocks can be carried with confidence to interesting dating problems, such as the age of the Earth itself. The currently agreed age of 4.6 billion years is the estimate upon which several different clocks converge. Such agreement is not surprising, but unfortunately we need to emphasize it because, astonishingly, as I pointed out in the Introduction (and have documented in the Appendix), some 40 per cent of the American population, and a somewhat smaller percentage of the British population, claim to believe that the age of the Earth, far from being measured in billions of years, is less than 10,000 years. Lamentably, especially in America and over much of the Islamic world, some of these history-deniers wield power over schools and their syllabuses. (Page 106)

Because plant, but not animal, cell walls are stiffened by cellulose. Herbivorous mammals like horses, cattle and elephants have great millstonelike teeth for grinding cellulose, quite different from the shearing teeth of carnivores and the needly teeth of insectivores. (Page 115)

Vegetarians also have characteristic peculiarities of the gut. Animals generally can't digest cellulose without the aid of bacteria or other micro-organisms, and many vertebrates set aside a blind alley in the gut called the caecum, which houses such bacteria and acts as a fermentation chamber (our appendix is a vestige of the larger caecum in our more vegetarian ancestors). (Page 115)

with the bacterium Escherichia coli, in a spectacular long-term experiment by the bacteriologist Richard Lenski and his colleagues at Michigan State University. (Page 117)

E. coli is a common bacterium. Very common. There are about a hundred billion billion of them around the world at any one time, of which about a billion, by Lenski's calculation, are in your large intestine at this very moment. (Page 117)

These bacteria reproduce asexually-by simple cell division-so it is easy to clone up a huge population of genetically identical individuals in a short time. In 1988, Lenski took one such population and infected twelve identical flasks, all of which contained the same nutrient broth, including glucose as the vital food source. The twelve flasks, each with its founding population of bacteria, were then placed in a 'shaking incubator' where they were kept nice and warm, and shaken to keep the bacteria well distributed throughout the liquid. These twelve flasks founded twelve lines of evolution that were destined to be kept separate from one another for two decades and counting: sort of like the twelve tribes of Israel, except that in the case of the tribes of Israel there was no law against their mixing.

Lenski's research shows, in microcosm and in the lab, massively speeded up so that it happened before our very eyes, many of the essential components of evolution by natural selection: random mutation followed by non-random natural selection; adaptation to the same environment by separate routes independently, the way successive mutations build on their predecessors to produce evolutionary change; the way some genes rely, for their effects, on the presence of other genes. Yet it all happened in a tiny fraction of the time evolution normally takes. (Page 130)

The guppies matured at a later age than in predator-infested streams, they were larger, and they produced fewer and larger offspring. The balance had shifted towards the norm for predator-free pools, where sexual attractiveness takes priority. (Page 139)

Dawkins opinion on religion is absurd since Evolution is nothing more than a religion itself you have to believe we all came from a single cell... and that a snail can become a monkey etc. Ha Ha - that's the most laughable religion yet!!

DNA as 'the Genetic Book of the Dead' (Page 179)

the way natural selection works, there is a sense in which the DNA of an animal is a textual description of the worlds in which its ancestors were naturally selected. For a fish, the genetic book of the dead describes ancestral seas. For us and most mammals, the early chapters of the book are all set in the sea and the later ones all out on land. For whales, dugongs, marine iguanas, penguins, seals, sea lions and turtles, there is a third section of the book which recounts their epic return to the proving grounds of their remote past, the sea. But for the land tortoises, perhaps twice independently on two widely separated occasions, there is yet a fourth section of the book devoted to a final or is it? - re-emergence, yet again to the land. (Page 180)

every animal of every species changes, during its own embryological development, far more dramatically than the typical adult form changes from generation to generation as the geological ages go by. (Page 207)

THAT irascible genius J. B. S. Haldane, who did so much else besides being one of the three leading architects of neoDarwinism, was once challenged by a lady after a public lecture. It's a word-of-mouth anecdote, and John Maynard Smith is sadly not available to confirm the exact words, but this is approximately how the exchange went:

We may be wonderfully developed' but we are not 'wonderfully made. When children sing 'He made their glowing colours / He made their tiny wings, they are uttering a childishly obvious falsehood. Whatever else God does, he certainly doesn't make glowing colours and tiny wings. If he did anything at all, it would be to supervise the embryonic development of things, for example by splicing together sequences of genes that direct a process of automated development. Wings are not made, they grow - progressively - from limb buds inside an egg. (Page 212)

The early history of embryology was riven between two opposing doctrines called preformationism and epigenesis. The distinction between them is not always clearly understood, so I shall spend a little time explaining these two terms. The preformationists believed that the egg (or sperm, for the preformationists were subdivided into ovists' versus 'spermists') contained a tiny miniature baby or 'homunculus. All the parts of the baby were intricately in place, correctly disposed to each other, waiting only to be inflated like a compartmentalized balloon. (Page 213)

Textbooks of biology repeat time and again that DNA is a 'blueprint' for building a body. It isn't. (Page 214)

DNA, then, is emphatically not a blueprint. Unlike Adam, who was fashioned directly into his adult form, all real bodies develop and grow from a single cell through the intermediate stages of embryo, foetus, baby, child and adolescent. (Page 215)

Principles of Development, by Lewis Wolpert and colleagues, describes epigenesis as the idea that new structures arise progressively. (Page 216)

happens in the building of a termite mound or an ant's nest - and in the development of an embryo. It is what makes embryology so remarkably different from anything we humans are familiar with, in the way of construction or manufacture. (Page 218)

The key point is that there is no choreographer and no leader.

The beautifully designed' body emerges as a consequence of rules being locally obeyed by individual cells, with no reference to anything that could be called an overall global plan. The cells of a developing embryo wheel and dance around each other like starlings in gigantic flocks. There are differences, and they are important. Unlike starlings, cells are physically attached to each other in sheets and blocks: their 'flocks' are called tissues. When they wheel and dance like miniature starlings, the consequence is that three-dimensional shapes are formed, as tissues invaginate in response to the movements of cells; or swell or shrink due to local patterns of growth and cell death. (Page 220)

Apoptosis is programmed cell death, and it is involved, for example, in the development of fingers and toes. In the human embryo, the fingers and toes are all joined. In the womb, you and I had webbed feet and hands. The webbing disappeared (in most people, there are occasional exceptions) through programmed cell death. (Page 221)

The viral DNA then hijacks the protein-making machinery of the bacterium, which is subverted into making new viruses. (Page 223)

In all cases their genetic material hijacks the protein-making apparatus of the host cell and diverts its molecular production line to churning out viruses instead of its normal products. (Page 223)

Let's call it 'auto-origami'. How does auto-origami work in practice, in embryology? It works because what happens in the real embryo, when a sheet of tissue grows, is that cells divide. And differential growth of the different parts of the sheet of tissue is achieved by the cells, in each part of the sheet, dividing at a rate determined by local rules. (Page 226)

The single fertilized egg cell divides to make two cells.

Gastrulation is a kind of microcosmic earthquake which sweeps over the blastula's surface and revolutionizes its entire form. (Page 226)

Gastrulation typically involves a denting of the hollow ball that is the blastula, so that it becomes two-layered with an opening to the outside world (see the computer simulation on p. 231). The outer layer of this gastrula is called the ectoderm, the inner layer is the endoderm, and there are also some cells thrown into the space between the ectoderm and endoderm, which are called mesoderm. (Page 227)

the outer skin and nervous system come from the ectoderm; the guts and other internal organs come from the endoderm; and the mesoderm furnishes muscle and bone. (Page 227)

In neurulation, as in gastrulation, invagination is much in evidence. (Page 227)

A section of ectoderm invaginates (progressively backwards along the body like a zip fastener), rolls itself up into a tube, and is pinched off where the sides of the tube zip up' so that it ends up running the length of the body between the outer layer and the notochord. That tube is destined to become the spinal cord, the main nerve trunk of the body. The front end of it swells up and becomes the brain. And all the rest of the nerves are derived, by subsequent cell divisions, from this primordial tube.* (Page 227)

Gastrulation and neurulation are accomplished early in development and they affect the whole shape of the embryo.

Cells multiply all through a sheet of tissue. Its area therefore increases and, having nowhere else to go, it has little choice but to buckle or invaginate. But the process is more controlled than that, and it has been deciphered by a group of scientists associated with the brilliant mathematical biologist George Oster, of the University of California at Berkeley. (Page 229)

An early classic experiment by the Nobel Prize-winning embryologist Roger Sperry illustrates the principle perfectly. Sperry and a colleague took a tadpole and removed a tiny square of skin from the back. They removed another square, the same size, from the belly. They then regrafted the two squares, but each in the other's place: the belly skin was grafted on the back, and the back skin on the belly. When the tadpole grew up into a frog, the result was rather pretty, as experiments in embryology often are: there was a neat postage stamp of white belly skin in the middle of the dark, mottled back, and another neat postage stamp of dark mottled skin in the middle of the white belly. And now for the point of the story.

People who believe in some sort of tabula rasa theory - whereby we are all born with a blank sheet for a mind, and fill it in by experience - must be surprised at Sperry's result. (Page 233)

What happens in normal embryonic development, according to Sperry's interpretation, is that axons (long 'wires, each one a narrow, tubular extension of a single nerve cell) grow questingly out from the spinal cord, sniffing like a dog for belly skin. Other axons grow out from the spinal cord, sniffing out back skin. And normally this gives the right result: tickles on the back feel as though they are on the back, while tickles on the belly feel as though they are on the belly.

Experiments like this led Sperry to formulate his 'chemo affinity hypothesis, according to which the nervous system wires itself up not by following an overall blueprint but by each individual axon seeking out end organs with which it has a particular chemical affinity. (Page 234)

Cell adhesion molecules are much more ingenious than that.

Protein molecules are virtuosos of the auto-origamic arts, on a scale much smaller than that of the sheets of cells we have so far dealt with. (Page 235)

Proteins are chains of smaller molecules called amino acids, and these chains, like the sheets of cells we have been considering, also fold themselves, in highly determined ways but on a much smaller scale. (Page 235)

Protein molecules, simply following the laws of chemistry and thermodynamics, spontaneously and automatically twist themselves into precisely shaped three-dimensional configurations (Page 236)

The auto-origami by which protein chains fold and coil themselves is ruled by the laws of chemical attraction, and the laws determining the angles at which atoms bind to one another. (Page 237)

The details of how the laws of chemistry determine the tertiary structure of a protein are not yet fully understood: chemists can't yet deduce. (Page 237)

Natural selection doesn't need to understand why a genetic change has a certain consequence.

The living cell, too, is a great chemistry lab, and it has a similarly large store of chemicals. But they aren't kept in separate bottles and jars on shelves. They are all mixed up together. It is as though a vandal, a chemical lord of misrule, entered the lab, seized all the bottles on all the shelves, and tipped them with anarchistic abandon into one great cauldron. Terrible thing to do? Well, it would be if they all reacted together, in all possible combinations. But they don't. Or if they do, the rate at which they react together is so slow that they might as well not be reacting at all. Except - and this is the whole point - if an enzyme is present. There is no need for glass bottles and jars to keep the substances apart because, to all intents and purposes, they are not going to react together anyway - unless the right enzyme is present. The equivalent of keeping the chemicals in stoppered bottles until you want to mix a particular pair, say A and B, is to mix all the hundreds of substances up in a great witch's brew, but supply only the right enzyme to catalyse the reaction between A and B and no other combination. Actually, the metaphor of the anarchically inclined bottle-tipper goes too far. Cells do contain an infrastructure of membranes between which, and within which, chemical reactions go on. To some extent, these membranes play the role of glass partitions between test tubes and flasks. (Page 239)

The point of this section of the chapter is that 'the right enzyme'

A cell is a versatile chemical factory, capable of spewing out massive quantities of a wide variety of different substances, the choice being made by which enzyme is present. And how is that choice made? By which gene is turned on. (Page 241)

Just as the cell is a vat filled with lots of chemicals, only a minority of which react with each other, so every cell nucleus contains the entire genome, but with only a minority of genes turned on. When a gene is turned on in, say, a cell of the pancreas, its sequence of code letters directly determines the sequence of amino acids in a protein; and the sequence of amino acids determines (remember the image of the magnetic necklace?) the shape into which the protein folds itself; and the shape into which the protein folds itself determines the precisely shaped sockets that marry up substances drifting around in the cell. (Page 242)

the whole course of embryonic development is controlled, via an intricate sequence of events, by genes. (Page 242)

Caenorhabditis elegans was chosen in the 1960s as an ideal experimental animal by the formidably brilliant South African biologist Sydney Brenner. He had recently completed his work, with Francis Crick and others at Cambridge, on cracking the genetic code (Page 244)

There is no overall plan of development, no blueprint, no architect's plan, no architect.

the gene knows nothing of this. All it is doing, within different bodies and in successive generations, is rejigging a carefully sculpted dent in a protein molecule. The rest of the story follows automatically, in branching cascades of local consequences, from which, eventually, a whole body emerges. (Page 249)

When you have a sufficient number of small entities cells, protein molecules, membranes - each at its own level obeying local rules and influencing others - then the eventual consequence is dramatic If genes survive or fail to survive as a consequence of their influence on such local entities and their behaviour, natural selection of successful genes - and the emergence of their successful products will inevitably follow, (Page 250)

of the millions of evolutionary divergences that have populated the Earth with such luxuriant diversity began with the chance separation of two subpopulations of a species, often, though not always, on either side of a geographical barrier such as a sea, a river, a mountain range or a desert valley (Page 256)

Before 4 October 1995 there were no members of the species Iguana iguana on the Caribbean island of Anguilla. On that date, a population of these large lizards suddenly appeared on the eastern side of the island. Fortuitously, they were actually seen arriving. They were clinging to a mat of driftwood and uprooted trees, some more than 30 feet long, that had drifted from a neighbouring island, probably Guadeloupe 160 miles away. (Page 257)

Seeing this gradation and diversity of structure in one small, intimately related group of birds, one might really fancy that from an original paucity of birds in this archipelago, one species had been taken and modified for different ends. In a like manner it might be fancied that a bird, originally a buzzard, had been induced here to undertake the office of the carrion-feeding Polybori of the American continent. (Page 260)

The theory of 'continental drift', as it used to be called, was first championed by the German climatologist Alfred Wegener (1880-1930). Wegener was not the first to look at a map of the world and notice that the shape of a continent or island often matches the coastline opposite as if the two land masses were pieces of a jigsaw puzzle, even when the opposite coastline is far away. (Page 273)

It is inspiring to think of the huge rift valley that must once have snaked its way down the continent of Gondwana between the future Africa and future South America. No doubt it was at first dotted with lakes like the present rift valley of East Africa. Later, it filled with sea water as South America sheared away with rending tectonic agony.

Madagascar and Africa were once part of the great southern continent of Gondwana, together with South America, Antarctica, India and Australia. (Page 281)

I have implied that the tree of resemblances is really a family tree, but are we forced to this conclusion? Are there any alternative interpretations? Well, just barely! The hierarchical pattern of resemblances was spotted by creationists in pre-Darwinian times, and they did have a non-evolutionary explanation - an embarrassingly far-fetched one. Patterns of resemblance, in their view, reflected themes in the mind of the designer. He had various ideas for how to make animals. His thoughts ran along a mammal theme, and, independently, they ran along an insect theme. Within the mammal theme, the designer's ideas were neatly and hierarchically bisected into sub-themes (say, the cloven-hoofed theme) and sub-sub-themes (say, the pig theme). There is a strong element of special pleading and wishful thinking about this, and nowadays creationists seldom resort to it. Indeed, as with the evidence from geographical distribution, which we discussed in the last chapter, they rarely discuss comparative evidence at all, preferring to stick to fossils, where they have been taught (wrongly) to think they are on promising ground. (Page 296)

feathers from their shared ancestor, which had feathers. No mammal is descended from that ancestor. It's as simple as that.* The tree of resemblances is a family tree. It is the same kind of story for every branch and every sub-branch and every sub-sub-branch of the tree of life. (Page 297)

Jonathan Hodgkin, Oxford's Professor of Genetics, knows of only three tentative exceptions to the rule that gene transfer is confined within species: in nematode worms, in fruit flies, and (in a bigger way) in bdelloid rotifers. (Page 303)

This last group is especially interesting because, uniquely among major groupings of eucaryotes, they have no sex. Could it be that they have been able to dispense with sex because they have reverted to the ancient bacterial way of exchanging genes? (Page 303)

It is a little-known fact that some dinosaurs had a ganglion in the pelvis, which was so large (at least relative to the brain in the head) as almost to deserve the title of second brain. This prompted the following delightfully witty verse by the American comic writer Bert Leston Taylor (1866-1921):

Evolution never happened by taking one adult form and coaxing it into the shape of another. Remember that every adult grows as an embryo. The mutations selected would have worked in the developing embryo by changing the rate of growth of parts of the body relative to other parts. (Page 310)

Evolution is not a genetically controlled distortion of one adult form into another; it is a genetically controlled alteration in a developmental program. (Page 314)

If you gradually heat DNA, there comes a point - somewhere around 85°C when the bonding between the two strands of the double helix breaks, and the two helices separate. You can think of 85°C, or whatever the temperature turns out to be, as a melting point. (Page 318)

The earliest large-scale study along these lines was done by a group of geneticists in New Zealand led by Professor David Penny.

Just as each radioactive isotope has its characteristic half-life, so each gene has a characteristic turnover rate - the rate at which new mutations typically go to fixation by random chance. Histone genes characteristically turn over at a rate of one mutation per billion years. Fibrinopeptide genes are a thousand times faster, with a turnover of one new mutation fixed per million years. Cytochrome-C and the suite of haemoglobin genes have intermediate turnovers, with times to fixation measured in millions to tens of millions of years. (Page 336)

The Expression of the Emotions, as Darwin was one of the first to appreciate in his book of that name. I can't resist sharing with you some lines - vintage Darwin - from that book:

Francis Sibson Esq. wrote: The muscles that open and close the blowhole, and that act upon the various sacs, form one of the most complicated yet most exquisitely adjusted pieces of machinery that either nature or art presents. The dolphin's blowhole goes to great lengths to correct a problem that would never have arisen at all if only it breathed with gills, like a fish. And many of the details of the blowhole can be seen as corrections to secondary problems that arose when the air intake migrated from the nostrils to the top of the head. A real designer would have planned it in the top of the head in the first place that's if he hadn't decided to abolish lungs and go for gills anyway. (Page 341)

dolphin's mammalian history is deeply etched into the wrinkled surface of its brain. It's a part of its mammalness, along with the placenta, milk, a four-chambered heart, a lower jaw having only a single bone, warm-bloodedness, and many other specifically mammalian features. (Page 343)

New Zealand's flightless parrots, whose flying ancestors apparently lived so recently that kakapos still try to fly although they lack the equipment to succeed. In the words of the immortal Douglas Adams, in Last Chance to See, It is an extremely fat bird. A good-sized adult will weigh about six or seven pounds, and its wings are just about good for wiggling about a bit if it thinks it's about to trip over something - but flying is completely out of the question. Sadly, however, it seems that not only has the kakapo forgotten how to fly, but it has also forgotten that it has forgotten how to fly. Apparently a seriously worried kakapo will sometimes run up a tree and jump out of it, whereupon it flies like a brick and lands in a graceless heap on the ground. (Page 345)

Worker ants have lost their wings, but not the capacity to grow wings. Their winged history still lurks within them. We know this because queen ants (and males) have wings, and workers are females who could have been queens but who, for environmental, not genetic, reasons failed to become queens.* Presumably worker ants lost their wings in evolution because they are a nuisance and get in the way underground. Poignant testimony to this is provided by queen ants, who use their wings once only, to fly out of the natal nest, find a mate, and then settle down to dig a hole for a new nest. As they begin their new life underground the first thing they do is lose their wings, in some cases by literally biting them off: painful (perhaps; who knows?)

The word 'troglobite' has been coined for an animal that lives only in the darkest part of caves and is so specialized that it can live nowhere else. Troglobites include salamanders, fish, shrimps, crayfish, millipedes, spiders, crickets and many other animals. They are very often white, having lost all pigment, and blind. They usually, however, retain vestiges of eyes. (Page 351)

Hermann von Helmholtz, the great nineteenth-century German scientist (you could call him a physicist, but his contributions to biology and psychology were greater), said, of the eye: 'If an optician wanted to sell me an instrument which had all these defects, I should think myself quite justified in blaming his carelessness in the strongest terms, and giving him back his instrument.' One reason why the eye seems better than Helmholtz, the physicist, judged it to be is that the brain does an amazing job of cleaning the images up afterwards, like a sort of ultra-sophisticated, automatic Photoshop. As far as optics are concerned, the human eye achieves its Zeiss/Nikon quality only in the fovea, the central part of the retina that we use for reading. When we scan a scene, we move the fovea over different parts, seeing each one in the utmost detail and precision, and the brain's Photoshop'

So, what the eye lacks in optics the brain makes up for with its sophisticated image-simulating software. (Page 353)

A favourite example, ever since it was pointed out to me by Professor J. D. Currey when he tutored me as an undergraduate, is the recurrent laryngeal nerve. It is a branch of one of the cranial nerves, those nerves that lead directly from the brain rather than from the spinal cord. One of the cranial nerves, the vagus (the name means 'wandering' and it is apt), has various branches, two of which go to the heart, and two on each side to the larynx (voice box in mammals). On each side of the neck, one of the branches of the laryngeal nerve goes straight to the larynx, following a direct route such as a designer might have chosen. The other one goes to the larynx via an astonishing detour. It dives right down into the chest, loops around one of the main arteries leaving the heart (a different artery on the left and right sides, but the principle is the same), and then heads back up the neck to its destination.

If you were to look at a human embryo about twenty-six days after conception you would see that the blood supply to the gills' strongly resembles the segmental blood supply to the gills of a fish. Over the following weeks of gestation the pattern of blood vessels becomes simplified by stages and loses its original symmetry, and by the time the infant is born its circulatory system has become strongly left-biased - quite unlike the neat symmetry of the fish-like early embryo. (Page 359)

Williams next mentions the pouch of that iconic Australian animal the koala, which not a great idea in an animal that spends its time clinging to tree trunks - opens downwards, instead of upwards as in a kangaroo. Once again, the reason is a legacy of history. Koalas are descended from a wombat-like ancestor.

To quote the American biologist Colin Pittendrigh, the whole thing is nothing but a 'patchwork of makeshifts pieced together, as it were, from what was available when opportunity knocked, and accepted in the hindsight, not the foresight, of natural selection (Page 371)

The natural economy is solar-powered. Photons from the sun rain down upon the entire daytime surface of the planet. Many photons do nothing more useful than heat up a rock or a sandy beach. A few find their way into an eye-yours, or mine, or the compound eye of a shrimp or the parabolic reflector eye of a scallop. Some may happen to fall on a solar panel - either a man-made one like those that, in a fit of green zeal, I have just installed on my roof to heat the bathwater, or a green leaf, which is nature's solar panel. (Page 375)

It appears that originally free living green bacteria were hijacked into plant cells, where they eventually evolved into what we now call chloroplasts. (Page 376)

And it is a neatly symmetrical fact that, just as the uphill chemistry of life is mostly taken care of by green bacteria thriving inside plant cells, so too the downhill chemistry of metabolism the slow burning of sugars and other fuels to release energy in cells of both animals and plants - is the special expertise of another class of bacteria, once freeliving but now reproducing themselves in larger cells, where they are known as mitochondria. Mitochondria and chloroplasts, descended from different kinds of bacteria, each built up their complementary chemical wizardries billions of years before the existence of any living organism visible to the naked eye. (Page 377)

all the energy that drives life comes ultimately from sunlight, trapped by plants. (Page 377)

Natural selection drives predator species to become ever better at catching prey, and it simultaneously drives prey species to become ever better at escaping them. (Page 381)

Before asserting that the deceptive appearance of a grasshopper or butterfly is unnecessarily detailed, we must first ascertain what are the powers of perception and discrimination of the insects' natural enemies. Not to do so is like asserting that the armour of a battle-cruiser is too heavy, or the range of her guns too great, without inquiring into the nature and effectiveness of the enemy's armament. The fact is that in the primeval struggle of the jungle, as in the refinements of civilized warfare,' we see in progress a great evolutionary armament race - whose results, for defence, are manifested in such devices as speed, alertness, armour, spinescence, burrowing habits, nocturnal habits, poisonous secretions, nauseous taste, and procryptic, aposematic, and mimetic coloration; and for offence, in such counter-attributes as speed, surprise, ambush, allurement, visual acuity, claws, teeth, stings, poison fangs, and anticryptic and alluring coloration. Just as greater speed in the pursued has developed in relation to increased speed in the pursuer; or defensive armour in relation to aggressive weapons; so the perfection of concealing devices has evolved in response to increased powers of perception. (Page 382)

And what that actually means is that genes for making the equipment to outsmart or outrun the other side build up in the gene pools on the two sides.

Nature gets the balance right. The world is full of genes for getting the balance right. (Page 385)

It is, of course, not the individual animals and plants that do the juggling and balancing. It is the relative numbers of alternative genes in gene pools that are juggled and balanced, by natural selection. (Page 386)

And just the same kinds of implicit calculation will balance up the optimum compromises in the predators. A cheetah who breaks her leg will undoubtedly die of starvation, and so will her cubs. But, depending on how difficult it is to find a meal, the risk of failing to catch enough food if she runs too slowly may outweigh the risk of breaking a leg through being equipped with the wherewithal to run too fast. (Page 386)

On the other hand, it is easy to see how a central planner, with the welfare of the whole community at heart, might umpire an agreement in the following terms, along the lines of the Forest of Friendship. Let both sides ‘agree' to scale down their armoury: both sides shift resources to other departments of life, and all will do better as a result. Just the same, of course, can happen in a human arms race. We wouldn't need our fighters if you didn't have your bombers.

The problem is that natural selection doesn't 'step in', natural selection doesn't look into the future, and natural selection doesn't choose between rival groups. (Page 390)

[N]ature is neither kind nor unkind. She is neither against suffering, nor for it. Nature is not interested in suffering one way or the other unless it affects the survival of DNA. It is easy to imagine a gene that, say, tranquillises gazelles when they are about to suffer a killing bite. Would such a gene be favoured by natural selection? Not unless the act of tranquillising a gazelle improved that gene's chances of being propagated into future generations. It is hard to see why this should be so and we may therefore guess that gazelles suffer horrible pain and fear when they are pursued to the death - as most of them eventually are. The total amount of suffering per year in the natural world is beyond all decent contemplation. During the minute that it takes me to compose this sentence, thousands of animals are being eaten alive, others are running for their lives, whimpering with fear, others are being slowly devoured from within by rasping parasites, thousands of all kinds are dying of starvation, thirst and disease. It must be so. If there is ever a time of plenty, this very fact will automatically lead to an increase in population until the natural state of starvation and misery is restored.

A virus exists for the sole purpose of making more viruses. Well, the same is ultimately true of tigers and snakes, but there it doesn't seem so futile. (Page 391)

Viruses and tigers are both built by coded instructions whose ultimate message is, like a computer virus, 'Duplicate me.' (Page 392)

In so far as natural selection can be said to 'want' anything, natural selection doesn't want individuals to sacrifice themselves for the love of a country, or for the sake of an ideology or a party or a group or a species. Natural selection is against' individuals over-ruling the warning sensations of pain. Natural selection wants' us to survive, or more specifically, to reproduce, and be blowed to country, ideology or their non-human equivalents. As far as natural selection is concerned, little red flags will be favoured only if they are never over-ruled. (Page 394)

As a matter of interest, there are aberrant individuals who cannot feel pain, and they usually come to a bad end. Congenital insensitivity to pain with anhidrosis' (CIPA) is a rare genetic abnormality in which the patient lacks pain receptor cells in the skin (and also - that's the 'anhidrosis' doesn't sweat). Admittedly, CIPA patients don't have a built-in 'red flag' system to compensate for the breakdown of the pain system, but you'd think they could be taught to be cognitively aware of the need to avoid bodily damage - a learned red flag system.

natural selection is indifferent to the intensity of suffering - except in so far as it affects survival and reproduction. (Page 395)

Ichneumon wasps, with their habit of paralysing but not killing their victim, before laying an egg in it with the promise of a larva gnawing it hollow from within, and the cruelty of nature generally, were major preoccupations of Victorian theodicy. It's easy to see why.

The appointment of death by the agency of carnivora, as the ordinary termination of animal existence, appears therefore in its main results to be a dispensation of benevolence; it deducts much from the aggregate amount of the pain of universal death; it abridges, and almost annihilates, throughout the brute creation, the misery of disease, and accidental injuries, and lingering decay; and imposes such salutary restraint upon excessive increase of numbers, that the supply of food maintains perpetually a due ratio to the demand. The result is, that the surface of the land and depths of the waters are ever crowded with myriads of animated beings, the pleasures of whose life are coextensive with its duration; and which throughout the little day of existence that is allotted to them, fulfill with joy the functions for which they were created. (Page 396)

it may not be a logical deduction, but to my imagination it is far more satisfactory to look at such instincts as the young cuckoo ejecting its fosterbrothers, -ants making slaves, - the larvae of ichneumonidae feeding within the live bodies of caterpillars, - not as specially endowed or created instincts, but as small consequences of one general law, leading to the advancement of all organic beings, namely, multiply, vary, let the strongest live and the weakest die. (Page 400)

Natural selection cares naught for any comfort. Why should it? For something to happen in nature, the only requirement is that the same happening in ancestral times assisted the survival of the genes promoting it. Gene survival is a sufficient explanation for the cruelty of wasps and the callous indifference of all nature: sufficient - and satisfying to the intellect if not to human compassion. (Page 400)

If animals aren't suffering, somebody isn't working hard enough at the business of gene survival. (Page 401)

You have to remember that, for all his personal modesty, Darwin nursed high ambitions. On his world-view, everything about the human mind, all our emotions and spiritual pretensions, all arts and mathematics, philosophy and music, all feats of intellect and of spirit, are themselves productions of the same process that delivered the higher animals. It is not just that without evolved brains spirituality and music would be impossible. More pointedly, brains were naturally selected to increase in capacity and power for utilitarian reasons, until those higher faculties of intellect and spirit emerged as a by-product, and blossomed in the cultural environment provided by group living and language. The Darwinian world-view does not denigrate the higher human faculties, does not 'reduce' them to a plane of indignity. It doesn't even claim to explain them at the sort of level that will seem particularly satisfying, in the way that, say, Darwinian explanation of a snake-mimicking caterpillar is satisfying.

The genetic database will become a storehouse of information about the environments of the past, environments in which ancestors survived and passed on the genes that helped them to do so. To the extent that present and future environments resemble those of the past (and mostly they do), this 'genetic book of the dead' will turn out to be a useful manual for survival in the present and future.

Each individual's genome, in any one generation, will be a sample from the species database. Different species will have different databases because of their different ancestral worlds. The database in the gene pool of camels will encode information about deserts and how to survive in them. The DNA in mole gene pools will contain instructions and hints for survival in dark, moist soil. The DNA in predator gene pools will increasingly contain information about prey animals, their evasive tricks and how to outsmart them. The DNA in prey gene pools will come to contain information about predators and how to dodge and outrun them. The DNA in all pools contains information about parasites and how to resist their pernicious invasions. (Page 406)

Information on how to handle the present so as to survive into the future is necessarily gleaned from the past. Non-random survival of DNA in ancestral bodies is the obvious way in which information from the past is recorded for future use, and this is the route by which the primary database of DNA is built up. But there are three further ways in which information about the past is archived in such a way that it can be used to improve future chances of survival. These are the immune system, the nervous system, and culture. Along with wings, lungs and all the other apparatus for survival, each of the three secondary information-gathering systems was ultimately prefigured by the primary one: natural selection of DNA. We could together call them the four 'memories. (Page 406)

The first memory is the DNA repository of ancestral survival techniques, written on the moving scroll that is the gene pool of the species. Just as the inherited database of DNA records the recurrent details of ancestral environments and how to survive them, the immune system, the 'second memory, does the same thing for diseases and other insults to the body during the individual's own lifetime. This database of past diseases and how to survive them is unique to each individual and is written in the repertoire of proteins that we call antibodies - one population of antibodies for each pathogen (disease-causing organism), precisely tailored by past experience' with the proteins that characterize the pathogen (Page 406)

I have fortunately never had polio, but medical science has cleverly devised the technique of vaccination for planting false memories of diseases never suffered. I shall never contract polio, because my body 'thinks' it has done so in the past, and my immune system database is equipped with the appropriate antibodies, 'fooled' into making them by the injection of a harmless version of the virus (Page 407)

The nervous system has a rule that says, 'Any trial action that is followed by reward should be repeated.

the third memory, the one in the brain, has spawned a fourth. The database in my brain contains more than just a record of the happenings and sensations of my personal life - although that was the limit when brains originally evolved. Your brain includes collective memories inherited non-genetically from past generations, handed down by word of mouth, or in books or, nowadays, on the internet.

his edition of his father's letters, Francis Darwin inserted a footnote telling us, On the same subject my father wrote in 1871: 'It is often said that all the conditions for the first production of a living organism are now present, which could ever have been present.

Oxygen flooded into the atmosphere as a pollutant, even a poison, until natural selection shaped living things to thrive on the stuff and indeed, suffocate without it. The reducing atmosphere inspired the most famous experimental attack on the problem of the origin of life, Stanley Miller's flask full of simple ingredients, which bubbled and sparked for only a week before yielding amino acids and other harbingers of life. (Page 418)

Self-replication spawns a population of entities, which compete with each other to be replicated. Since no copying process is perfect, the population will inevitably come to contain variety, and if variants exist in a population of replicators those that have what it takes to succeed will come to predominate. This is natural selection, and it could not start until the first self-replicating entity came into existence (Page 419)

proteins are outstandingly bad at, and this Darwin overlooked. They are completely hopeless at replication. They can't make copies of themselves. This means that the key step in the origin of life cannot have been the spontaneous arising of a protein. (Page 420)

RNA belongs to the same family of chain molecules as DNA, the polynucleotides. It is capable of carrying what amount to the same four code 'letters' as DNA, and it indeed does so in living cells, carrying genetic information from DNA to where it can be used. DNA acts as the template for RNA code sequences to build up. And then protein sequences build up using RNA, not DNA, as their template.

I find the RNA World theory plausible, and I think it quite likely that chemists will, within the next few decades, simulate in the laboratory a full reconstruction of the events that launched natural selection on its momentous way four billion years ago. Fascinating steps in the right direction have already been taken. (Page 421)

I shall be using the name history-deniers' for those people who deny evolution: who believe the world's age is measured in thousands of years rather than thousands of millions of years, and who believe humans walked with dinosaurs.

Ernst Mayr, grand old man of the neo-Darwinian synthesis, who died in 2005 at the age of 100, repeatedly voiced a different suspicion. For Mayr, the culprit was the ancient philosophical doctrine of -to give it its modern name - essentialism. The discovery of evolution was held back by the dead hand of Plato.*

For Plato, the reality that we think we see is just shadows cast on the wall of our cave by the flickering light of the camp fire.

Biology, according to Mayr, is plagued by its own version of essentialism. Biological essentialism treats tapirs and rabbits, pangolins and dromedaries, as though they were triangles, rhombuses, parabolas or dodecahedrons. The rabbits that we see are wan shadows of the perfect idea of rabbit, the ideal, essential, Platonic rabbit, hanging somewhere out in conceptual space along with all the perfect forms of geometry. Fleshand-blood rabbits vary, but their variations are always to be seen as flawed deviations may from the ideal essence of rabbit.

Alfred Russel Wallace, independent co-discoverer with Darwin of evolution by natural selection, actually called his paper 'On the tendency of varieties to depart indefinitely from the original type.

All is fluid, as another Greek philosopher, Heraclitus, said; nothing fixed. After a hundred million years it may be hard to believe that the descendant animals ever had rabbits for ancestors. Yet in no generation during the evolutionary process was the predominant type in the population far from the modal type in the previous generation or the following generation. This way of thinking is what Mayr called population thinking. Population thinking, for him, was the antithesis of essentialism. According to Mayr, the reason Darwin was such an unconscionable time arriving on the scene was that we all - whether because of Greek influence or for some other reason - have essentialism burned into our mental DNA.

Indeed, psychologists studying the development of language tell us that children are natural essentialists. Maybe they have to be if they are to remain sane while their developing minds divide things into discrete categories each entitled to a unique noun.

The word 'essentialism' itself wasn't invented till 1945 and so was not available to Darwin. But he was only too familiar with the biological version of it in the form of the 'immutability of species, and much of his effort was directed towards combating it under that name. Indeed, in several of Darwin's books - more so in others than On the Origin of Species itself - you'll understand fully what he's on about only if you shed modern presuppositions about evolution, and remember that a large part of his audience would have been essentialists who never doubted the immutability of species.

The idea of a gene pool is central to the body of knowledge and theory that goes under the name of the 'Neo-Darwinian Synthesis'.

The concept of a gene pool has meaning only in the light of Mendel's law of the independent assortment of hereditary particles. Darwin never knew Mendel's laws, for although Gregor Mendel, the Austrian monk who was the father of genetics, was Darwin's contemporary, he published his findings in a German journal which Darwin never saw.

Mendel showed that this is because when paternal genes and maternal genes are combined in a child (he didn't use the word 'gene, which wasn't coined until 1909), it is not like blending paints, it is more like shuffling and reshuffling cards in a pack. Nowadays, we know that genes are lengths of DNA code, not physically separate like cards, but the principle remains valid. Genes don't blend; they shuffle.

Spencer's term... 'Survival of the Fittest'.