Flowers Again
Let's now, in the third of our warm-up forays into natural selection, move on to flowers and pollinators and see something of the power of natural selection to drive evolution. Pollination biology furnishes us with some pretty amazing facts, and the high point of wondrousness is reached in the orchids. No wonder Darwin was so keen on them no wonder he wrote the book I have already mentioned, The Various Contrivances by which Orchids are Fertilised by Insects. Some orchids, such as the 'magic...
Radioactive Clocks
Let's now turn to radioactive clocks. There are quite a lot of them to choose from, and, as I said, they blessedly cover the gamut from centuries to thousands of millions of years. Each one has its own margin of error, which is usually about 1 per cent. So if you want to date a rock which is billions of years old, you must be satisfied with an error of plus or minus tens of millions of years. If you want to date a rock hundreds of millions of years old, you must be satisfied with an error of...
You Are My Natural Selection
Are there other examples of selective breeding by non-human eyes Oh yes. Think of the dull, camouflaged plumage of a hen pheasant, compared with the splendiferous male of the same species. There seems little doubt that, if his individual survival were the only thing that mattered, the cock golden pheasant would 'prefer' to look like the female, or like a grown-up version of how he was as a chick. The female and the chicks are obviously well camouflaged, and that's the way the male would be too...
Tree Rings
A tree-ring clock can be used to date a piece of wood, say a beam in a Tudor house, with astonishing accuracy, literally to the nearest year. Here's how it works. First, as most people know, you can age a newly felled tree by counting rings in its trunk, assuming that the outermost ring represents the present. Rings represent differential growth in different seasons of the year - winter or summer, dry season or wet season - and they are especially pronounced at high latitudes, where there is a...
How dendrochronology works
Tree rings are not quite the only system that promises total accuracy to the nearest year. Varves are layers of sediment laid down in glacial lakes. Like tree rings, they vary seasonally and from year to year, so theoretically the same principle can be used, with the same degree of accuracy. Coral reefs, too, have annual growth rings, just like trees. Fascinatingly, these have been used to detect the dates of ancient earthquakes. Tree rings too, by the way, tell us the dates of earthquakes....
Insects Were The First Domesticators
Roses tell the same story as dogs, but with one difference, which is relevant to our softening-up strategy. The flower of the rose, even before human eyes and noses embarked on their work of genetic chiselling, owed its very existence to millions of years of very similar sculpting by insect eyes and noses well, antennae, which is what insects smell with . And the same is true of all the flowers that beautify our gardens. The sunflower, Helianthus annuus, is a North American plant whose wild...
Rats Teeth
Why, if it is so easy to improve the teeth of rats by artificial selection, did natural selection apparently make such a poor job of it in the first place Surely there is no benefit in tooth decay. Why, if artificial selection is capable of reducing it, didn't natural selection do the same job long ago I can think of two answers, both instructive. The first answer is that the original population that the human selectors used as their raw material consisted not of wild rats but of domesticated...
Nature As The Selecting Agent
Let me draw this chapter, and the previous one, to a conclusion. Selection - in the form of artificial selection by human breeders - can turn a pye-dog into a Pekinese, or a wild cabbage into a cauliflower, in a few centuries. The difference between any two breeds of dog gives us a rough idea of the quantity of evolutionary change that can be achieved in less than a millennium. The next question we should ask is, how many millennia do we have available to us in accounting for the whole history...
Contents
The primrose path to macro-evolution Missing link What do you mean,'missing' Arms races and 'evolutionary theodicy' There is grandeur in this view of life APPENDIX The history-deniers 427 BIBLIOGRAPHY AND FURTHER READING 447
Contents 1
Chapter 3 The primrose path to macro-evolution Chapter 6 Missing link What do you mean, 'missing' Chapter 7 Missing persons Missing no longer Chapter 8 You did it yourself in nine months Chapter 11 History written all over us Chapter 12 Arms races and 'evolutionary theodicy' Chapter 13 There is grandeur in this view of life BIBLIOGRAPHY AND FURTHER READING PICTURE ACKNOWLEDGEMENTS INDEX
Dogs Again
Having finally reached the topic of natural selection, we can turn back to the example of dogs for some other important lessons. I said that they are domesticated wolves, but I need to qualify this in the light of a fascinating theory of the evolution of the dog, which has again been most clearly articulated by 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...
Domestication
This chapter is mostly about selection by eyes, but other senses can do the same thing. Fanciers have bred canaries for their songs, as well as for their appearance. The wild canary is a yellowish brown finch, not spectacular to look at. Human selective breeders have taken the palette of colours thrown up by random genetic variation and manufactured a colour distinctive enough to be named after the bird canary yellow. By the way, the bird itself is named after the islands, not the other way...
Chapter 2 Dogs Cows And Cabbages
Why did it take so long for a Darwin to arrive on the scene What delayed humanity's tumbling to that luminously simple idea which seems, on the face of it, so much easier to grasp than the mathematical ideas given us by Newton two centuries earlier - or, indeed, by Archimedes two millennia earlier Many answers have been suggested. Perhaps minds were cowed by the sheer time it must take for great change to occur - by the mismatch between what we now call geological deep time and the lifespan and...
Chapter 3 The Primrose Path To Macroevolution
Chapter 2 showed how the human eye, working by selective breeding over many generations, sculpted and kneaded dog flesh to assume a bewildering variety of forms, colours, sizes and behaviour patterns. But we are humans, accustomed to making choices that are deliberate and planned. Are there other animals that do the same thing as human breeders, perhaps without deliberation or intention but with similar results Yes, and they carry this book's softening-up program steadily forward. This chapter...
Conchomorphs computergenerated shells shaped by artificial selection
Darwin had first-hand experience of the power of artificial selection and he gave it pride of place in Chapter 1 of On the Origin of Species. He was softening his readers up to take delivery of his own great insight, the power of natural selection. If human breeders can transform a wolf into a Pekinese, or a wild cabbage into a cauliflower, in just a few centuries or millennia, why shouldn't the non-random survival of wild animals and plants do the same thing over millions of years That will be...
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. Like other classical Greek thinkers, Plato was at heart a geometer. Every triangle drawn in the sand is but an imperfect shadow of the true essence of triangle. The lines of the essential triangle are pure Euclidean lines with length but no breadth, lines defined as infinitely narrow and as never meeting when parallel. The angles of the essential triangle really...
Biomorphs from the Blind Watchmaker program
So much for the genetics. The game starts to get interesting when we consider the 'embryology'. The embryology of a biomorph on the screen is the process by which its 'genes' - those numerical values -influence its shape. Many very different embryologies can be imagined, and I have tried out quite a few of them. My first program, called 'Blind Watchmaker', uses a tree-growing embryology. A main 'trunk' sprouts two 'branches', then each branch sprouts two branches of its own, and so on. The...