15 September 2008

On this day in 1835

...the HMS Beagle arrived at the Galapagos Islands. In addition to being a particularly auspicious moment in history and therefore worthy of mention, it gives me another welcome excuse to post this picture.

Beagle off the Galapagos by John Chancellor.
© Dr Gordon Chancellor and reproduced with his kind permission.

The Galapagos Archipelago is covered in Chapter XVII of The Voyage of the Beagle by Charles Darwin; the chapter contains this wonderful table indicating how many plant species are endemic to the Galapagos Archipelago, and, of those, how many are endemic to a single island.

Plants of the Galapagos Archipelago as published in The Voyage of the Beagle.

Island endemism (as evidenced in Darwin's own experience initially by tortoise shell shape and mockingbird distribution) was a (if not the) key clue that got Darwin's mind set on a path towards natural selection. In Darwin's words,
"The distribution of the tenants of this archipelago would not be nearly so wonderful, if, for instance, one island had a mocking-thrush, and a second island some other quite distinct genus;—if one island had its genus of lizard, and a second island another distinct genus, or none whatever;—or if the different islands were inhabited, not by representative species of the same genera of plants, but by totally different genera, as does to a certain extent hold good; for, to give one instance, a large berry-bearing tree at James Island has no representative species in Charles Island. But it is the circumstance, that several of the islands possess their own species of the tortoise, mocking-thrush, finches, and numerous plants, these species having the same general habits, occupying analogous situations, and obviously filling the same place in the natural economy of this archipelago, that strikes me with wonder. It may be suspected that some of these representative species, at least in the case of the tortoise and of some of the birds, may hereafter prove to be only well-marked races; but this would be of equally great interest to the philosophical naturalist."
Read the rest of Chapter XVII, "The Galapagos Archipelago", of Voyage of the Beagle here.

4 comments:

George Beccaloni (aka Wallace's Rottweiler) said...

Sorry to nitpick, but the quote you cited makes it seem that Darwin began pondering evolution whilst on the Beagle voyage after he had made observations on Galapagos tortoise shell shape, mockingbird distribution etc. However, this is a popular myth which came about because Darwin inserted passages into the second (1845) edition of his account of the Beagle voyage, which were written AFTER he had become an evolutionist and after he had discovered natural selection [the first edition of his account of the voyage was published in 1839]. On the voyage he was not an evolutionist and he didn't make much of the Galapagos tortoises or the mockingbirds he observed. It was only in 1837 a year after he returned from the voyage that he became convinced of the reality of evolution, largely thanks to the findings of specialists who had been studying his Galapagos specimens. He went on to discover natural selection in 1838 and had a pretty well worked out theory by the time he came to produce the second (1845) edition of his "Journal of researches into the natural history and geology of the countries visited during the voyage of H.M.S. Beagle round the world, under the Command of Capt. Fitz Roy, R.N.".

Karen James said...

Hi George, I don't disagree with anything you've said here, in fact I have gone to some pains in other posts here and in comments elsewhere to dispel this very same 'Galapagos epiphany' myth that you say I've fanned up by citing this particular quote. That was not my intention, which was why I called island endemism a 'clue' that got Darwin's mind 'set on a path' towards natural selection. I thought that pretty well conveyed that he didn't give birth to the idea right then and there, but perhaps I wasn't forceful enough. I think anyone who reads the Voyage of the Beagle will realise that it is not a diary but rather a retrospective, and I didn't mean to imply otherwise. Anyways, thanks for weighing in and keepin' me honest!

Karen James said...

p.s. my understanding is that an argument can be made that the fact that the different kinds of mockingbirds were exclusive to the different islands was immediately significant to Darwin, right then and there on the Galapagos. This is not to say that they triggered some eureka about natural selection, but that, for the first time, he observed the phenomenon that we now call island endemism. After this, he started piecing together similar anecdotes such that by the time the Beagle sailed around the Cape of Good Hope, he was already actively looking for more examples of the same. What I was trying to get across in my post is that the mockingbirds and tortoise shells (not the falsely fabled finches) were a seed that got him thinking - while still on the voyage - about the potential 'instability' of species. He hatched this somewhere between Cocos (Keeling) Islands and the Cape of Good Hope, as documented in his Ornithological notes and annotations by scholars thereon (see Nora Barlow's footnote on pp 262-3 Barlow, Nora ed. 1963. Darwin's ornithological notes. Bulletin of the British Museum (Natural History). Historical Series Vol. 2, No. 7. With introduction, notes and appendix by the editor.)

George Beccaloni (aka Wallace's Rottweiler) said...

Interesting what you said about Darwin noticing differences in the mockingbirds whilst still on the voyage. An important point in my initial post is that the second (and subsequent editions) of Darwin's account of the Beagle voyage is not a strictly contemporary account of the trip, since it contains Darwin's later thoughts. Many people (including some historians!) have not realised this, and this has led to error and confusion. I am not sure whether the first edition is free of later interpretation, so I guess it would be safest to consult Darwin's original Beagle Diary (http://darwin-online.org.uk/content/frameset?itemID=EHBeagleDiary&viewtype=text&pageseq=1) if one wants to learn what he thought about things such as evolution, whilst on the voyage.