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.

Darwin and wildlife photography at the NHM

I went along to the Natural History Museum to visit a couple of exhibitions: Wildlife Photographer of the Year and Darwin.

The WPotY exhibition is an annual treat; some years are  better than others, but it’s never less than enjoyable. My long-term gripe is that the overall winner is almost always a portrait of a large charismatic mammal (usually one of the African big games species) rather than ever being a picture of a shrimp or a toadstool or something. This year I’m willing to give them a partial credit on that front; they’ve picked a picture of a big cat, but it’s the fabulous, rare and extremely elusive snow leopard, and the picture, a night-time shot with falling snow, is pretty great.

You can see all the pictures online, but they also put the show on in other venues around the UK and around the world, so if South Kensington isn’t convenient you still might be able to see it somewhere near you. The shot above is of a polar bear at sunrise. Cool, innit. And how about this one, of leafcutter ants carrying petals:

The Darwin exhibition, part of the build-up to his 200th birthday next year, takes us through his life and work, and is full of artefacts (notebooks, letters) and specimens he collected. It does a good job of telling us about his life, I think, although as I’ve read two biographies of Darwin, and the Voyage of the Beagle, and The Origin of Species, and a biography of his grandfather, and one of Huxley, most of the material was familiar to me. I did enjoy it — it’s good to see all his scribbly handwriting and there are some great items on show — but none of it was really news to me, so I may not be the key audience.

btw, if you’re going to the museums at South Ken, you could do worse than have lunch at Casa Brindisa. Brindisa are a Spanish food importer with a shop in Borough Market who now have three tapas bars, and the lunch I had in there was just excellent. The website has the menu on it, so I can tell you exactly what I had: the pan fried sea bream with morcilla de Burgos and Bierzo peppers, a herb salad with moscatel vinaigrette and a serving of patatas bravas. It was all really delicious; the fish was crisp and perfectly cooked and went beautifully with earthiness of the morcilla and the slightly spicy peppers; the salad was fresh and herby with just enough slightly sweet dressing, and the potatoes were golden and crunchy without being oily and not drowned in the sauce. They even make an excellent cup of coffee, which is almost harder to find than a good plate of food.

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.

Links

  • 'The Orwell Prize, Britain’s pre-eminent prize for political writing, is publishing George Orwell’s diaries as a blog. From 9th August 2008, Orwell’s domestic and political diaries (from 9th August 1938 until October 1942) will be posted in real-time, exactly 70 years after the entries were written.'
    (del.icio.us tags: GeorgeOrwell diaries 1930s )
  • Good stuff from Darwin's Beagle diary today: 'Shortly after passing the first spring we came in sight of the famous tree, which the Indians reverence as a God itself, or as the altar of Walleechu… Being winter the tree had no leaves, but in their place were countless threads by which various offerings had been suspended.'
    (del.icio.us tags: CharlesDarwin C19th Argentina )

Darwin waxing lyrical

Charles Darwin was in an unusually poetical mood 175 years ago today:

The night was pitch dark, with a fresh breeze. — The sea from its extreme luminousness presented a wonderful & most beautiful appearance; every part of the water, which by day is seen as foam, glowed with a pale light. The vessel drove before her bows two billows of liquid phosphorus, & in her wake was a milky train. — As far as the eye reached, the crest of every wave was bright; & from the reflected light, the sky just above the horizon was not so utterly dark as the rest of the Heavens. — It was impossible to behold this plain of matter, as it were melted & consuming by heat, without being reminded of Milton’s description of the regions of Chaos & Anarchy.

More Darwiniana later today, possibly.

‘amongst other things’

Today’s entry from Darwin’s Beagle diary:

29th May 1832
Rio de Janeiro
Cloudy greyish day, something like an Autumnal one in England; without however its soothing quietness. I wanted to send a note this morning into the city & had the greatest difficulty in procuring anybody to take it. All white men are above it, & every black about here is a slave. This, amongst other things, is one great inconvenience of a slave country.

Darwin was in fact strongly anti-slavery. As a grandson of Josiah Wedgwood he was probably brought up that way, but his experiences visiting Brazil reinforced it and stayed with him for the rest of his life. Still, it’s not the most felicitous bit of phrasing.

Darwin’s prose

I recently found Charles Darwin’s Beagle Diary, being posted ‘live’ on the internet with a mere 175 year time-lag (see also Pepys, Thoreau).

He’s only just reached Brazil, so there’s plenty of time to join the fun. This is from today’s entry:

The houses are white and lofty and from the windows being narrow and long have a very light and elegant appearance. Convents, Porticos and public buildings vary the uniformity of the houses: the bay is scattered over with large ships; in short the view is one of the finest in the Brazils. But their beauties are as nothing compared to the Vegetation; I believe from what I have seen Humboldts glorious descriptions are and will for ever be unparalleled: but even he with his dark blue skies and the rare union of poetry with science which he so strongly displays when writing on tropical scenery, with all this falls far short of the truth. The delight one experiences in such times bewilders the mind, if the eye attempts to follow the flight of a gaudy butter-fly, it is arrested by some strange tree or fruit; if watching an insect one forgets it in the stranger flower it is crawling over, if turning to admire the splendour of the scenery, the individual character of the foreground fixes the attention. The mind is a chaos of delight, out of which a world of future and more quiet pleasure will arise. I am at present fit only to read Humboldt; he like another Sun illumines everything I behold.

A little on the flowery Victorian side, but still a fine bit of prose. What’s interesting is that you’d never know he could do it on the basis of The Origin of Species, a book which is well written but rarely sparkling. But in the diaries, notebooks and letters he can be a lively, engaging writer. One of my favourite quotes from the notebooks: ‘He who understands baboon would do more towards metaphysics than Locke’.

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