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Nature

The Greatest Show on Earth by Richard Dawkins

Full title: The Greatest Show on Earth: The Evidence for Evolution. I don’t need any persuading about the fact of evolution, but Dawkins is always worth reading on the subject. And Amazon had it at 50% off, so as much as I dislike hardbacks I thought I’d give it a go.

Since I’ve read so many books on evolution, not least the half dozen by Dawkins, what I’m really looking for in a book like this is interesting new examples I haven’t encountered before, and there are certainly some of those, like the wingless fly that lives in termite mounds; generally, though, a lot of it is fairly familiar: Tiktaalik, the evolution of the whale, the guppy experiment, Lenski’s E. coli, eyeless cave-dwelling animals and so on. There are good reasons why these examples are popular, of course, and if you don’t read as much about evolution as I do, they may well be unfamiliar to you. It’s certainly a different repertoire than it would have been ten or fifteen years ago. And Dawkins writes engagingly and clearly, even in the chapter about embryology, a subject I usually find a complete head-fuck. So I certainly enjoyed reading it.

The review in New Scientist complains about his occasional side-swipes at religion. The book doesn’t actually talk about religion as often as that review might suggest, but when it does touch on it, it’s about as unflattering as you would expect. It’s easy to understand why creationism is such a red rag to a biologist: his analogy is of a teacher of Latin and Roman history who is constantly confronted by people who insist that the Roman Empire never happened and that the myth of ‘Rome’ is a conspiracy. His abrasive manner when he talks about religion doesn’t bother me, although I can see there’s an argument that it is bad tactics in the battle for hearts and minds.

At least in this book he confines his comments to creationism rather than religion more generally; and I for one am not going to tell him he should be respectful towards young Earth creationism. Because 40% of the US population (and 22% of the UK) believe the world is less than 10,000 years old, when you are rude about creationists, you are being rude about an awful lot of people, and I’m sure they are largely nice, well-meaning and valuable members of society; but come on! Believing that the world is less than 10,000 years old is like believing that the Earth is flat, or that leprechauns bury pots of gold at the ends of rainbows. Or indeed that if you dilute poison over and over again until it is just water, it magically gains healing powers. These ideas are worthy of mockery.

So, I enjoyed it; I’d rather read Dawkins on evolution than Dawkins on religion any day of the week, mainly because evolution is a much more interesting subject. I’m not sure it’s an instant classic, but it’s well worth reading.

» The photo is © Troy Li and used under a CC by-nc-nd licence.

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Nature

Your Inner Fish by Neil Shubin

Your Inner Fish is a book which uses comparisons between human anatomy and the anatomy of other animals, living or extinct, to show how evolution helps explain the way we are and the way our bodies develop. Shubin is the palaeontologist who discovered Tiktaalik, one of the key fossils in understanding the fish/tetrapod transition, so that features somewhat, but he also draws on a wide range of examples from other species. tiktaalik

So for example, he traces the evolution of fin into hand over evolutionary history, but also examines how the growing embryo creates a hand (or a fin) from a blob of undifferentiated cells. He uses the evolutionary relationship between the structure of the human head and the gill arches of a shark to explain why the nerves of the head have such a peculiar relationship, how hiccuping is related to our amphibian ancestry, and so on.

Most of this material is rather technical and many of the examples were somewhat familiar to me, so the book could easily have been either impenetrable or just dull. In fact I found it worked very well; even when I had encountered some of the examples before, having them all put together into one book was very helpful. I really did feel after reading it that I was more in touch with my inner fish (and inner wormy thing, for that matter).

And it’s well written, as well. There was a rather clumsy bit in one the first chapter where he attempts to explain cladistics via a visit to the zoo, which had me worried that the book was going to be aimed at eleven-year-olds, but fortunately it turned out to be a blip. Generally the book seems well-pitched for intelligent adults who are curious about biology.

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Nature

Darwin’s other finches

The Galapagos finches are an icon of evolution. But you don’t have to go all the way to the Galapagos to see finches which have evolved different beaks and different body shapes in order to specialise for different kinds of food and different lifestyles.

These are all species of finch that Darwin might conceivably have seen in his garden in Kent, or perhaps when he dropped off his family at the church on Sunday and went for a country walk while they were in the service. Some would have been common; others are long shots. I’ve arranged them in approximate order of beak size in the classic Galapagos fashion.

The reason the Galapagos finches make such a good teaching example is that even to a casual observer they look closely related. Indeed, from personal experience I can say that they offer a tricky identification problem: when you have several species which are only distinguished by size and shape of beak, and those features are highly variable within the species anyway… it can be frustrating.

It’s very easy to use them to tell a straightforward story of a few original finches — maybe just a single pair — being blown across to the islands from South America, and then, as the population grew and split between different islands, diverging to fit into slightly different lifestyles. It is the evolutionary process reduced to the simplest possible case.

The evolutionary history of the species pictured here is no doubt rather more complicated; rather than being isolated on an oceanic archipelago, they are part of a family that ranges around the whole northern hemisphere and into Africa. And they look rather more distinct than the Galapagos species.

Even so, apart from a general similarity of body shape and behaviour, there are some suggestions in the plumage that these birds are related. The fact that so many species of finch have one or two pale wingbars is probably not a coincidence. And, after all, that’s what we mean when we say that species are part of the same family: they are all descended from some single ancestral species of finch. Perhaps that original finch had wingbars. Notice as well that they nearly all have slightly forked tails.

And although the story of these finches is so much more complicated and wide-ranging than the Galapagos species, it is essentially the same thing. Those first few finches may not have been isolated on an oceanic island, but it is still a story of a few ancestral birds, somewhere, who bred and spread into different areas, formed different populations, and adapted to subtly different ecological niches. There are still plenty of similarities; they are basically seed eaters, they tend to have complex songs, they are largely arboreal. But they vary from goldfinches who eat thistle seeds to hawfinches with a beak strong enough to crack open a cherry stone.

Darwin actually mentions finches in The Origin of Species. Since 1859, we have become more used to the idea that taxonomical groups (like ‘finches’) equate to shared bloodlines. But the things we know intellectually may still be hard to internalise. So it’s not surprising that, before he had told the world his idea, Darwin found people were uncomfortable with it:

when I first kept pigeons and watched the several kinds, knowing well how true they bred, I felt fully as much difficulty in believing that they could have descended from a common parent, as any naturalist could in coming to a similar conclusion in regard to the many species of finches, or other large groups of birds, in nature. One circumstance has struck me much; namely, that all the breeders of the various domestic animals and the cultivators of plants, with whom I have ever conversed, or whose treatises I have read, are firmly convinced that the several breeds to which each has attended, are descended from so many aboriginally distinct species. Ask, as I have asked, a celebrated raiser of Hereford cattle, whether his cattle might not have descended from long-horns, and he will laugh you to scorn. I have never met a pigeon, or poultry, or duck, or rabbit fancier, who was not fully convinced that each main breed was descended from a distinct species. Van Mons, in his treatise on pears and apples, shows how utterly he disbelieves that the several sorts, for instance a Ribston-pippin or Codlin-apple, could ever have proceeded from the seeds of the same tree. Innumerable other examples could be given. The explanation, I think, is simple: from long-continued study they are strongly impressed with the differences between the several races; and though they well know that each race varies slightly, for they win their prizes by selecting such slight differences, yet they ignore all general arguments, and refuse to sum up in their minds slight differences accumulated during many successive generations. May not those naturalists who, knowing far less of the laws of inheritance than does the breeder, and knowing no more than he does of the intermediate links in the long lines of descent, yet admit that many of our domestic races have descended from the same parents—may they not learn a lesson of caution, when they deride the idea of species in a state of nature being lineal descendants of other species?

The Galapagos finches, incidentally, are not actually ‘true’ finches. That is, they are not members of the Fringillidae, the family that includes all the species pictured here. They were previously thought to be in the Emberizidae, another large family of seed-eating birds including the buntings, American sparrows, juncos and towhees. But apparently (and I’m only getting my information here from Wikipedia) the latest thinking is that they are tanagers.

Meanwhile, DNA testing has shown another notable island family, the Hawaiian honeycreepers, are in fact finches that have evolved to become nectar eating, with long, narrow curved beaks like sunbirds. And the euphonias, a group of blue and yellow birds that were previously thought to be tanagers, have been moved into the finches as well.

These changes are part of a revolution in taxonomy that has been enabled by DNA testing technology. How Darwin would have loved it.

» The finches pictured are, from top to bottom: siskin, redpoll, goldfinch, chaffinch, brambling, linnet, greenfinch, bullfinch, crossbill and hawfinch.

All the pictures except the goldfinch and the linnet are © Sergey Yeliseev and used under a Creative Commons by-nc-nd licence. The goldfinch is © Isidro Vila Verde and used under a by-nc licence. The linnet is © Ian-S and used under a by-nc-nd licence.

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Culture Nature

The Origin of Species by Charles Darwin

The final chapter of The Origin of Species — Darwin’s ‘Recapitulation and Conclusion’ — states the case for evolution as well as any short account I have ever read. It’s tightly written, it argues a case, it summarises all the different kinds of evidence and shows clearly why they are important. It’s pithy, confident: great stuff. 

Which left me feeling look, Darwin, if you can write like that, why have the previous 400 pages been such hard work? Because he did produce some turgid paragraphs. He’s better when he’s talking about specifics — particular animals and experiments — but when he gets into generalities and abstract ideas, his prose often turns to mush. Here’s a sample sentence: 

The forms which possess in some considerable degree the character of species, but which are so closely similar to other forms, or are so closely linked to them by intermediate gradations, that naturalists do not like to rank them as distinct species, are in several respects the most important for us.

OK, that’s not particularly difficult to understand, but it doesn’t have a lot of oomph, either. Not much forward momentum to keep the reader going.

Large-flowered Bee Ophrys

That sentence is taken from the chapter ‘Variation under nature’, and part of the problem in that chapter and elsewhere is that Darwin is struggling against the limitations of his knowledge. Variation and heredity are absolutely central to the idea of natural selection, so of course he has to talk about them a lot; but without knowing about genetics, let alone DNA. And at times he seems to be floundering a bit. I’m very aware, reading it, of how much he doesn’t know; I’m curious how much he felt that lack of knowledge himself. He certainly had enough evidence of other kinds to argue convincingly that all living things evolved from a common ancestor, and that natural selection was a plausible explanation for how it happened; but without genetics there is certainly a jigsaw piece missing.

That’s not the only gap which is obvious with hindsight: for example, he talks about the distribution of species as evidence for common descent, but without continental drift, there are certain details he can’t quite explain. So if someone wanted to understand evolution, they should start with a more modern text. I suppose the question is: why read The Origin at all? Well, the immediate reason I re-read it is that we’re currently building up to Darwin Year. 2008 is the 150th anniversary of the first publication of the Darwin/Wallace theory of natural selection at a meeting of the Linnean Society, and 2009 is both 150 years since the publication of The Origin of Species and also Darwin’s 200th birthday.

earthworm

Also, it may be hard going by the standards of modern popular science writers, but for one of the key documents in the history of science, it’s incredibly (perhaps uniquely) accessible. I haven’t actually tried reading James Clerk Maxwell’s original papers on electromagnetism, or Einstein’s on relativity, but I don’t think it’s defeatist to say I wouldn’t understand them. Darwin is entirely manageable for a non-technical reader. He uses some technical terminology without defining it, so you might be checking the glossary a bit if you don’t know, for example, that ‘cirripedes’ are barnacles; but the book is mostly dealing with familiar concepts and entities: species and varieties, pigeons, bees, flowers. The only comparison that springs to mind is another book written at the early stages of a science, when scientists were still grappling with everyday concepts and the visible world: Galileo’s Dialogue Relating to Two New Sciences (which, by the way, is well worth reading).

And when Darwin hits his stride, when he gets stuck into the details, the book is still full of interesting material. For example, discussing the means by which plants are distributed between places:

I do not believe that botanists are aware how charged the mud of ponds is with seeds. I have tried several little experiments, but will here give only the most striking case. I took, in February, three table-spoonfuls of mud from three different points, beneath water, on the edge of a little pond. This mud, when dry, weighed only 6¾ ounces. I kept it covered up in my study for six months, pulling up and counting each plant as it grew. The plants were of many kinds, and were altogether 537 in number; and yet the viscid mud was all contained in a breakfast cup! Considering these facts, I think it would be an inexplicable circumstance if water-birds did not transport the seeds of fresh-water plants to vast distances, and if consequently the range of these plants was not very great. The same agency may have come into play with the eggs of some of the smaller fresh-water animals.

That passage is a great demonstration of Darwin’s practical turn of mind. For someone who is known for having produced a famous theory, he was a great experimentalist. Faced with the argument that, for example, seeds couldn’t be distributed on ocean currents because salt water would kill them, he tried the experiment, leaving seeds in salt water for different periods of time to see if they would still germinate. He wanted to know more about the process of selective breeding in domestic animals, so he started breeding fancy pigeons. He wanted to know how inherited instinct could enable bees to make such elaborate and perfect honeycombs, so he provided a hive of bees with specially prepared blocks of wax to see what they would do with them.

goose barnacles

If anything the book is more convincing as an argument for the historical fact of evolution — common descent with gradual changes over time — than the theory of natural selection. He does make a good case for natural selection, mainly by analogy with selective breeding in domestic animals, but because he didn’t know about genetics or DNA, there’s an inherent fuzziness about the details right at the centre.

But his argument for evolution is I think particularly strong because he was consciously writing for an audience of educated people who believed in the immutability of species. So he points out that varieties (what we now usually call subspecies) blur indistinguishably into species, so that experts frequently disagree whether to classify them as full species or not. That different continents have basically different flora and fauna; so the animals in the Amazon are related to those of the Andes rather than those of the Congo, even though the Congo is a much more similar habitat. And oceanic islands normally have very limited fauna; that what they do have tends to be those animals that can fly (insects, birds and bats, but not other mammals) or can survive salt water (reptiles but not amphibians). And again, that the inhabitants of those islands are related to the inhabitants of the nearest continent, even when the island habitat is quite different. All these facts are easily explained by evolution; there is no reason why any of them would need to be true if species were created in place.

» To illustrate this post I thought I’d break away from the most obvious stuff (Galapagos finches etc) to pick some of the other things Darwin studied: orchids, earthworms and barnacles. The orchid photo is one I took in Crete; the earthworm is by Jonathan Spangler and is used under a CC by-sa licence; the goose barnacles are by pshab and used under a by-nc licence.

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