"The Greatest Show on Earth "
by Richard Dawkins
by Richard Dawkins
Dogs , Cows and cabbages
The dead hand of plato
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. Flesh-and-blood rabbits may vary, but their variations are always to be seen as flawed deviations from the ideal essence of rabbit.
How desperately unevolutionary that picture is! The Platonist regards any change in rabbits as a messy departure from the essential rabbit, and there will always be resistance to change – as if all real rabbits were tethered by an invisible elastic cord to the Essential Rabbit in the Sky. The evolutionary view of life is radically opposite. Descendants can depart indefinitely from the ancestral form, and each departure becomes a potential ancestor to future variants. Indeed, Alfred Russel Wallace, independent codiscoverer with Darwin of evolution by natural selection, actually called his paper ‘On the tendency of varieties to depart indefinitely from the original type’.
For any two animals there has to be a hairpin path linking them, for the simple reason that every species shares an ancestor with every other species: all we have to do is walk backwards from one species to the shared ancestor, then turn through a hairpin bend and walk forwards to the other species. We are talking only about locating a chain of animals that links a modern animal to another modern animal. We are most emphatically not evolving a rabbit into a leopard. Modern species don’t evolve into other modern species, they just share ancestors: they are cousins.
However radical and extensive the differences between the ends of the hairpin – rabbit and leopard, say – each step along the chain that links them is very, very small. Every individual along the chain is as similar to its neighbours in the chain as mothers and daughters are expected to be.
The dead hand of plato
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. Flesh-and-blood rabbits may vary, but their variations are always to be seen as flawed deviations from the ideal essence of rabbit.
How desperately unevolutionary that picture is! The Platonist regards any change in rabbits as a messy departure from the essential rabbit, and there will always be resistance to change – as if all real rabbits were tethered by an invisible elastic cord to the Essential Rabbit in the Sky. The evolutionary view of life is radically opposite. Descendants can depart indefinitely from the ancestral form, and each departure becomes a potential ancestor to future variants. Indeed, Alfred Russel Wallace, independent codiscoverer with Darwin of evolution by natural selection, actually called his paper ‘On the tendency of varieties to depart indefinitely from the original type’.
For any two animals there has to be a hairpin path linking them, for the simple reason that every species shares an ancestor with every other species: all we have to do is walk backwards from one species to the shared ancestor, then turn through a hairpin bend and walk forwards to the other species. We are talking only about locating a chain of animals that links a modern animal to another modern animal. We are most emphatically not evolving a rabbit into a leopard. Modern species don’t evolve into other modern species, they just share ancestors: they are cousins.
However radical and extensive the differences between the ends of the hairpin – rabbit and leopard, say – each step along the chain that links them is very, very small. Every individual along the chain is as similar to its neighbours in the chain as mothers and daughters are expected to be.
Sculpting the gene pool
Cabbages are a vegetable affront to essentialism and the immutability of species. The wild cabbage, Brassica oleracea, is an undistinguished plant, vaguely like a weedy version of a domestic cabbage. In just a few centuries, wielding the fine and coarse chisels furnished by the toolbox of selective breeding techniques, horticulturalists have sculpted this rather nondescript plant into vegetables as strikingly different from each other and from the wild ancestor as broccoli, cauliflower, kohlrabi, kale, Brussels sprouts, spring greens, romanescu and, of course, the various kinds of vegetables that are still commonly called cabbage.
The relevance to natural evolution is that, although the selecting agent is man and not nature, the process is otherwise exactly the same. This is why Darwin gave so much prominence to domestication at the beginning of On the Origin of Species. Anybody can understand the principle of evolution by artificial selection. Natural selection is the same, with one minor detail changed.
A Mendelian gene is an all-or-nothing entity. When you were conceived, what you received from your father was not a substance, to be mixed with what you received from your mother as if mixing blue paint and red paint to make purple. If this were really how heredity worked (as people vaguely thought in Darwin’s time) we’d all be a middling average, halfway between our two parents. In that case, all variation would rapidly disappear from the population (no matter how assiduously you mix purple paint with purple paint, you’ll never reconstitute the original red and blue). In fact, of course, anybody can plainly see that there is no such intrinsic tendency for variation to decrease in a population. 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.
Any one of your eggs (or sperms if you are male) contains either your father’s version of a particular gene or your mother’s version, not a blend of the two. And that particular gene came from one and only one of your four grandparents; and from one and only one of your eight great-grandparents.
A sexually reproducing population, such as, say, all the rats on Ascension Island, remotely isolated in the South Atlantic, is continually shuffling all the genes on the island. There is no intrinsic tendency for each generation to become less variable than the previous generation, no tendency towards ever more boringly grey, middling intermediates. The genes remain intact, shuffled about from individual body to individual body as the generations go by, but not blending with one another, never contaminating each other.
There is no intrinsic tendency in gene pools for particular genes to increase or decrease in frequency. But when there is a systematic increase or decrease in the frequency with which we see a particular gene in a gene pool, that is precisely and exactly what is meant by evolution.
Mutations are the random changes in genes that constitute the raw material for evolution by non-random selection.
Without any understanding at all, just by choosing who mates with whom, you can breed for all kinds of desired characteristics. This is what dog breeders, and animal and plant breeders generally, achieved for centuries before anybody understood anything about genetics. And there’s a lesson in that about natural selection, for nature, of course, has no understanding or awareness of anything at all.
First, the great variety among breeds of dogs, from Great Danes to Yorkies, from Scotties to Airedales, from ridgebacks to dachshunds, from whippets to St Bernards, demonstrates how easy it is for the non-random selection of genes – the ‘carving and whittling’ of gene pools – to produce truly dramatic changes in anatomy and behaviour, and so fast.
Cabbages are a vegetable affront to essentialism and the immutability of species. The wild cabbage, Brassica oleracea, is an undistinguished plant, vaguely like a weedy version of a domestic cabbage. In just a few centuries, wielding the fine and coarse chisels furnished by the toolbox of selective breeding techniques, horticulturalists have sculpted this rather nondescript plant into vegetables as strikingly different from each other and from the wild ancestor as broccoli, cauliflower, kohlrabi, kale, Brussels sprouts, spring greens, romanescu and, of course, the various kinds of vegetables that are still commonly called cabbage.
The relevance to natural evolution is that, although the selecting agent is man and not nature, the process is otherwise exactly the same. This is why Darwin gave so much prominence to domestication at the beginning of On the Origin of Species. Anybody can understand the principle of evolution by artificial selection. Natural selection is the same, with one minor detail changed.
A Mendelian gene is an all-or-nothing entity. When you were conceived, what you received from your father was not a substance, to be mixed with what you received from your mother as if mixing blue paint and red paint to make purple. If this were really how heredity worked (as people vaguely thought in Darwin’s time) we’d all be a middling average, halfway between our two parents. In that case, all variation would rapidly disappear from the population (no matter how assiduously you mix purple paint with purple paint, you’ll never reconstitute the original red and blue). In fact, of course, anybody can plainly see that there is no such intrinsic tendency for variation to decrease in a population. 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.
Any one of your eggs (or sperms if you are male) contains either your father’s version of a particular gene or your mother’s version, not a blend of the two. And that particular gene came from one and only one of your four grandparents; and from one and only one of your eight great-grandparents.
A sexually reproducing population, such as, say, all the rats on Ascension Island, remotely isolated in the South Atlantic, is continually shuffling all the genes on the island. There is no intrinsic tendency for each generation to become less variable than the previous generation, no tendency towards ever more boringly grey, middling intermediates. The genes remain intact, shuffled about from individual body to individual body as the generations go by, but not blending with one another, never contaminating each other.
There is no intrinsic tendency in gene pools for particular genes to increase or decrease in frequency. But when there is a systematic increase or decrease in the frequency with which we see a particular gene in a gene pool, that is precisely and exactly what is meant by evolution.
Mutations are the random changes in genes that constitute the raw material for evolution by non-random selection.
Without any understanding at all, just by choosing who mates with whom, you can breed for all kinds of desired characteristics. This is what dog breeders, and animal and plant breeders generally, achieved for centuries before anybody understood anything about genetics. And there’s a lesson in that about natural selection, for nature, of course, has no understanding or awareness of anything at all.
First, the great variety among breeds of dogs, from Great Danes to Yorkies, from Scotties to Airedales, from ridgebacks to dachshunds, from whippets to St Bernards, demonstrates how easy it is for the non-random selection of genes – the ‘carving and whittling’ of gene pools – to produce truly dramatic changes in anatomy and behaviour, and so fast.
The primrose path to macro-evolution
Insects were the first domesticators
‘Mammoth’ sunflowers, originally bred in Russia, are 12 to 17 feet high, the head diameter is close to one foot, which is more than ten times the size of a wild sunflower’s disc, and there is normally only one head per plant, instead of the many, much smaller, flowers of the wild plant. The Russians started breeding this American flower, by the way, for religious reasons. During Lent and Advent, the use of oil in cooking was banned by the Orthodox Church. Conveniently, and for a reason that I – untutored in the profundities of theology – shall not presume to fathom, sunflower seed oil was deemed to be exempt from this prohibition. This provided one of the economic pressures that drove the recent selective breeding of the sunflower. Long before the modern era, however, native Americans had been cultivating these nutritious and spectacular flowers for food, for dyes and for decoration, and they achieved results intermediate between the wild sunflower and the extravagant extremes of modern cultivars. But before that again, sunflowers, like all brightly coloured flowers, owed their very existence to selective breeding by insects.
Generations of ancestral flowers were chosen by generations of ancestral insects or hummingbirds or other natural pollinators. It is a perfectly good example of selective breeding, with the minor difference that the breeders were insects and hummingbirds, not humans.
It is of the essence of sexual reproduction that you shouldn’t fertilize yourself. Pollen must somehow be transported from one plant to another. Hermaphroditic plants that have male and female parts within one flower often go to elaborate lengths to stop the male half from fertilizing the female half.
Pollen is a fine, light powder. If you release enough of it on a breezy day, one or two grains may have the luck to land on the right spot in a flower of the right species. But wind pollination is wasteful. The vast majority of pollen grains land somewhere other than where they should, and all that energy and costly matériel is wasted. There is a more directed way for pollen to be targeted. Nectar is sugary syrup, and it is manufactured by plants specifically and only for paying, and fuelling, bees, butterflies, hummingbirds, bats and other hired transport.
Both Darwin and his co-discoverer of natural selection, Wallace, called attention to an amazing orchid from Madagascar, Angraecum sesquipedale and both men made the same remarkable prediction, which was later triumphantly vindicated. This orchid has tubular nectaries that reach down more than 11 inches by Darwin’s own ruler. That’s nearly 30 centimetres. A related species, Angraecum longicalcar, has nectar-bearing spurs that are even longer, up to 40 centimetres (more than 15 inches). Darwin, purely on the strength of A. sesquipedale’s existence in Madagascar, predicted in his orchid book of 1862 that there must be ‘moths capable of extension to a length of between ten and eleven inches’. Wallace, five years later (it isn’t clear whether he had read Darwin’s book) mentioned several moths whose probosces were nearly long enough to meet the case.
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. Flowers that look plain to us may actually be lavishly decorated with spots or stripes for the benefit of insects, ornamentation that we can’t see because we are blind to ultraviolet.
This floral extravaganza, splashed across the green canvas of a meadow, has been shaped and coloured, magnified and titivated by the past choices made by animal eyes: bee eyes, butterfly eyes, hoverfly eyes. In New World forests we’d have to add hummingbird or in African forests sunbird eyes to the list. Hummingbird eyes, hawk-moth eyes, butterfly eyes, hoverfly eyes, bee eyes are critically cast over wild flowers, generation after generation, shaping them, colouring them, swelling them, patterning and stippling them, in almost exactly the same way as human eyes later did with our garden varieties; and with dogs, cows, cabbages and corn.
For the flower, insect pollination represents a huge advance in economy over the wasteful scattergun of wind pollination. Even if a bee visits flowers indiscriminately, lurching promiscuously from buttercup to cornflower, from poppy to celandine, a pollen grain clinging to its hairy abdomen has a much greater chance of hitting the right target – a second flower of the same species – than it would have if scattered on the wind. Slightly better would be a bee with a preference for a particular colour, say blue. Or a bee that, while not having any long-term colour preference, tends to form colour habits, so that it chooses colours in runs. Better still would be an insect that visits flowers of only one species. And there are flowers, like the Madagascar orchid that inspired the Darwin/Wallace prediction, whose nectar is available only to certain insects that specialize in that kind of flower and benefit from their monopoly over it. Those Madagascar moths are the ultimate magic bullets.
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 well-trained homing pigeons. Each side could be said to have domesticated the other, selectively breeding them to do a better job than they previously did. Human breeders of prize roses have had almost exactly the same kinds of effects on flowers as insects have – just exaggerated them a bit. Insects bred flowers to be bright and showy. Gardeners made them brighter and showier still. Insects made roses pleasantly fragrant. We came along and made them even more so. Incidentally, it is a fortunate coincidence that the fragrances that bees and butterflies prefer happen to appeal to us too.
The insects, by choosing the most attractive flowers to visit, inadvertently ‘breed for’ floral beauty. At the same time, the flowers are breeding the insects for pollination ability. Then again, 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).
You are my natural selection
Bright colours may indeed attract predators, but they attract female pheasants too. Generations of hens chose to mate with bright, glowing males, rather than the dull brown creatures that the males would surely have remained but for selective breeding by females. The same thing happened with peahens selectively breeding peacocks, female birds of paradise breeding males, and numerous other examples of birds, mammals, fish, amphibians, reptiles and insects where females (it’s usually females rather than males) choose from among competing males.
Deep-sea angler fish sit on the bottom of the sea, waiting patiently for prey. Like many deep-sea fish, anglers are spectacularly ugly by our standards. May be by fish standards too, although it probably doesn’t matter because, down where they live, it is too dark to see much anyway. Like other denizens of the deep sea, female angler fish often make their own light – or rather, they have special receptacles in which they house bacteria which make light for them. Such ‘bioluminescence’ isn’t bright enough to reflect any detail, but it is bright enough to attract other fish. A spine becomes elongated and stiffened to make a fishing rod. On the end of the fishing rod is a bait, or lure. The baits vary from species to species, but they always resemble small food items: perhaps a worm, or a small fish, or just a nondescript but temptingly jiggling morsel. Often the bait is actually luminous: another natural neon sign, and in this case the message being flashed is ‘come and eat me’. Small fish are indeed tempted. They approach close to the bait. And it is the last thing they do for, at that moment, the angler opens her huge maw and the prey is engulfed with the inrush of water. The prey fish are indeed choosing the most ‘attractive’ angler fish for breeding, via the indirect route of choosing them for survival by feeding them! Anglers with unattractive lures are more likely to starve to death and therefore less likely to breed. And the small prey fish are indeed doing the ‘choosing’. But they are choosing with their lives!
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. 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. The general case is the non-random survival of randomly varying hereditary equipment.
It may be said that natural selection is daily and hourly scrutinising, throughout the world, every variation, even the slightest; rejecting that which is bad, preserving and adding up all that is good; silently and insensibly working, whenever and wherever opportunity offers, at the improvement of each organic being in relation to its organic and inorganic conditions of life. We see nothing of these slow changes in progress, until the hand of time has marked the long lapse of ages, and then so imperfect is our view into long past geological ages, that we see only that the forms of life are now different from what they formerly were.
Wallace went on to quote a French author called Janet, who was evidently, unlike Wallace and Darwin, a deeply muddled individual:
I see that he considers your weak point to be that you do not see that ‘thought and direction are essential to the action of Natural Selection.’ The same objection has been made a score of times by your chief opponents, and I have heard it as often stated myself in conversation. Now, I think this arises almost entirely from your choice of the term Natural Selection, and so constantly comparing it in its effects to man’s selection, and also to your so frequently personifying nature as ‘selecting’, as ‘preferring’ . . . etc., etc. To the few this is as clear as daylight, and beautifully suggestive, but to many it is evidently a stumbling-block. I wish, therefore, to suggest to you the possibility of entirely avoiding this source of misconception in your great work, and also in future editions of the ‘Origin,’ and I think it may be done without difficulty and very effectually by adopting Spencer’s term . . . ‘Survival of the Fittest.’ This term is the plain expression of the fact; ‘Natural Selection’ is a metaphorical expression of it . . .
Experimental interference is of enormous importance, because without it you can never be sure that a correlation you observe has any causal significance. This can be illustrated by the so-called ‘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. It is only experimental manipulation that can determine whether an observed correlation truly indicates causation.
Artificial selection is not just an analogy for natural selection. Artificial selection constitutes a true experimental – as opposed to observational – test of the hypothesis that selection causes evolutionary change.
Insects were the first domesticators
‘Mammoth’ sunflowers, originally bred in Russia, are 12 to 17 feet high, the head diameter is close to one foot, which is more than ten times the size of a wild sunflower’s disc, and there is normally only one head per plant, instead of the many, much smaller, flowers of the wild plant. The Russians started breeding this American flower, by the way, for religious reasons. During Lent and Advent, the use of oil in cooking was banned by the Orthodox Church. Conveniently, and for a reason that I – untutored in the profundities of theology – shall not presume to fathom, sunflower seed oil was deemed to be exempt from this prohibition. This provided one of the economic pressures that drove the recent selective breeding of the sunflower. Long before the modern era, however, native Americans had been cultivating these nutritious and spectacular flowers for food, for dyes and for decoration, and they achieved results intermediate between the wild sunflower and the extravagant extremes of modern cultivars. But before that again, sunflowers, like all brightly coloured flowers, owed their very existence to selective breeding by insects.
Generations of ancestral flowers were chosen by generations of ancestral insects or hummingbirds or other natural pollinators. It is a perfectly good example of selective breeding, with the minor difference that the breeders were insects and hummingbirds, not humans.
It is of the essence of sexual reproduction that you shouldn’t fertilize yourself. Pollen must somehow be transported from one plant to another. Hermaphroditic plants that have male and female parts within one flower often go to elaborate lengths to stop the male half from fertilizing the female half.
Pollen is a fine, light powder. If you release enough of it on a breezy day, one or two grains may have the luck to land on the right spot in a flower of the right species. But wind pollination is wasteful. The vast majority of pollen grains land somewhere other than where they should, and all that energy and costly matériel is wasted. There is a more directed way for pollen to be targeted. Nectar is sugary syrup, and it is manufactured by plants specifically and only for paying, and fuelling, bees, butterflies, hummingbirds, bats and other hired transport.
Both Darwin and his co-discoverer of natural selection, Wallace, called attention to an amazing orchid from Madagascar, Angraecum sesquipedale and both men made the same remarkable prediction, which was later triumphantly vindicated. This orchid has tubular nectaries that reach down more than 11 inches by Darwin’s own ruler. That’s nearly 30 centimetres. A related species, Angraecum longicalcar, has nectar-bearing spurs that are even longer, up to 40 centimetres (more than 15 inches). Darwin, purely on the strength of A. sesquipedale’s existence in Madagascar, predicted in his orchid book of 1862 that there must be ‘moths capable of extension to a length of between ten and eleven inches’. Wallace, five years later (it isn’t clear whether he had read Darwin’s book) mentioned several moths whose probosces were nearly long enough to meet the case.
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. Flowers that look plain to us may actually be lavishly decorated with spots or stripes for the benefit of insects, ornamentation that we can’t see because we are blind to ultraviolet.
This floral extravaganza, splashed across the green canvas of a meadow, has been shaped and coloured, magnified and titivated by the past choices made by animal eyes: bee eyes, butterfly eyes, hoverfly eyes. In New World forests we’d have to add hummingbird or in African forests sunbird eyes to the list. Hummingbird eyes, hawk-moth eyes, butterfly eyes, hoverfly eyes, bee eyes are critically cast over wild flowers, generation after generation, shaping them, colouring them, swelling them, patterning and stippling them, in almost exactly the same way as human eyes later did with our garden varieties; and with dogs, cows, cabbages and corn.
For the flower, insect pollination represents a huge advance in economy over the wasteful scattergun of wind pollination. Even if a bee visits flowers indiscriminately, lurching promiscuously from buttercup to cornflower, from poppy to celandine, a pollen grain clinging to its hairy abdomen has a much greater chance of hitting the right target – a second flower of the same species – than it would have if scattered on the wind. Slightly better would be a bee with a preference for a particular colour, say blue. Or a bee that, while not having any long-term colour preference, tends to form colour habits, so that it chooses colours in runs. Better still would be an insect that visits flowers of only one species. And there are flowers, like the Madagascar orchid that inspired the Darwin/Wallace prediction, whose nectar is available only to certain insects that specialize in that kind of flower and benefit from their monopoly over it. Those Madagascar moths are the ultimate magic bullets.
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 well-trained homing pigeons. Each side could be said to have domesticated the other, selectively breeding them to do a better job than they previously did. Human breeders of prize roses have had almost exactly the same kinds of effects on flowers as insects have – just exaggerated them a bit. Insects bred flowers to be bright and showy. Gardeners made them brighter and showier still. Insects made roses pleasantly fragrant. We came along and made them even more so. Incidentally, it is a fortunate coincidence that the fragrances that bees and butterflies prefer happen to appeal to us too.
The insects, by choosing the most attractive flowers to visit, inadvertently ‘breed for’ floral beauty. At the same time, the flowers are breeding the insects for pollination ability. Then again, 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).
You are my natural selection
Bright colours may indeed attract predators, but they attract female pheasants too. Generations of hens chose to mate with bright, glowing males, rather than the dull brown creatures that the males would surely have remained but for selective breeding by females. The same thing happened with peahens selectively breeding peacocks, female birds of paradise breeding males, and numerous other examples of birds, mammals, fish, amphibians, reptiles and insects where females (it’s usually females rather than males) choose from among competing males.
Deep-sea angler fish sit on the bottom of the sea, waiting patiently for prey. Like many deep-sea fish, anglers are spectacularly ugly by our standards. May be by fish standards too, although it probably doesn’t matter because, down where they live, it is too dark to see much anyway. Like other denizens of the deep sea, female angler fish often make their own light – or rather, they have special receptacles in which they house bacteria which make light for them. Such ‘bioluminescence’ isn’t bright enough to reflect any detail, but it is bright enough to attract other fish. A spine becomes elongated and stiffened to make a fishing rod. On the end of the fishing rod is a bait, or lure. The baits vary from species to species, but they always resemble small food items: perhaps a worm, or a small fish, or just a nondescript but temptingly jiggling morsel. Often the bait is actually luminous: another natural neon sign, and in this case the message being flashed is ‘come and eat me’. Small fish are indeed tempted. They approach close to the bait. And it is the last thing they do for, at that moment, the angler opens her huge maw and the prey is engulfed with the inrush of water. The prey fish are indeed choosing the most ‘attractive’ angler fish for breeding, via the indirect route of choosing them for survival by feeding them! Anglers with unattractive lures are more likely to starve to death and therefore less likely to breed. And the small prey fish are indeed doing the ‘choosing’. But they are choosing with their lives!
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. 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. The general case is the non-random survival of randomly varying hereditary equipment.
It may be said that natural selection is daily and hourly scrutinising, throughout the world, every variation, even the slightest; rejecting that which is bad, preserving and adding up all that is good; silently and insensibly working, whenever and wherever opportunity offers, at the improvement of each organic being in relation to its organic and inorganic conditions of life. We see nothing of these slow changes in progress, until the hand of time has marked the long lapse of ages, and then so imperfect is our view into long past geological ages, that we see only that the forms of life are now different from what they formerly were.
Wallace went on to quote a French author called Janet, who was evidently, unlike Wallace and Darwin, a deeply muddled individual:
I see that he considers your weak point to be that you do not see that ‘thought and direction are essential to the action of Natural Selection.’ The same objection has been made a score of times by your chief opponents, and I have heard it as often stated myself in conversation. Now, I think this arises almost entirely from your choice of the term Natural Selection, and so constantly comparing it in its effects to man’s selection, and also to your so frequently personifying nature as ‘selecting’, as ‘preferring’ . . . etc., etc. To the few this is as clear as daylight, and beautifully suggestive, but to many it is evidently a stumbling-block. I wish, therefore, to suggest to you the possibility of entirely avoiding this source of misconception in your great work, and also in future editions of the ‘Origin,’ and I think it may be done without difficulty and very effectually by adopting Spencer’s term . . . ‘Survival of the Fittest.’ This term is the plain expression of the fact; ‘Natural Selection’ is a metaphorical expression of it . . .
Experimental interference is of enormous importance, because without it you can never be sure that a correlation you observe has any causal significance. This can be illustrated by the so-called ‘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. It is only experimental manipulation that can determine whether an observed correlation truly indicates causation.
Artificial selection is not just an analogy for natural selection. Artificial selection constitutes a true experimental – as opposed to observational – test of the hypothesis that selection causes evolutionary change.