…They are as black as the porous rocks over which they crawl & seek their prey as from the Sea. — Somebody calls them “imps of darkness”. — They assuredly well become the land they inhabit. — When on shore I proceeded to botanize & obtained 10 different flowers; but such insignificant, ugly little flowers, as would better become an Arctic, than a Tropical country. — The birds are Strangers to Man & think us him as innocent as their countrymen the huge Tortoises. Little birds within 3 & four feet, quietly hopped about the Bushes & were not frightened by stones being thrown at them.” [Darwin’s Beagle Diary (1831-1836)].

And thus we get a hint of Darwin’s impressions of the Galapagos, and in particular, that Island’s marine iguanas.

The Iguana family is Iguanidae, but most Iguana’s you’ve cuddled in the pet store are members of the genus Iguana (and most likely species Iguana iguana.) The Galapagos Islands have two or three species of iguana: The Land Iguana is Conolophus subcristatus and Conolophus pallidus, or perhaps is actually the subspecies Conolophus subcristatus pallidus. The marine iguana is Amblyrhynchus cristatus.

The two genera of iguana on the Galapagos seem able to interbreed, though they otherwise also seem to make good, distinctive species. (No, it is not really true that inability to inbreed is “THE biological definition of species….” it is more complex than that. A topic for another time, perhaps.) The phylogenetic relationship among the Galapagos iguanas and continental iguanas is similar to that among the finches and other Galapagos animals… complex and more complex because of the apparent fact that while the oldest of the Galapagos islands is about four million years old, earlier islands, perhaps going back twice that age, formerly existed but are now eroded down below sea level. One wonders what will happen next ice age (or what happened last ice age) when a 120 -150 meter drop in sea level exposes some of these islands! The point is that these volcanic islands have a complex history, and it is likely that the islands themselves have a complex relationship to the distant continent. Again, the topic of another post perhaps.

The following passages from Darwin (1839) Continue reading Charles Darwin Bicentennial – Iguanas, a “most disgusting, clumsy lizard… →

Last Darwin Post I gave you the famous “Tangled Bank” quote, in which Darwin links the concept of selection to the concept of ecology and thus derives “grandeur in this view of life.”

This is a theme of much of Darwin’s writing in The Origin, and in fact, the Phrase “Tangled Bank” shows up much earlier in the volume.

In the case of every species, many different checks, acting at different periods of life, and during different seasons or years, probably come into play; some one check or some few being generally the most potent, but all concur in determining the average number or even the existence of the species. In some cases it can be shown that widely-different checks act on the same species in different districts. When we look at the plants and bushes clothing an entangled bank, we are tempted to attribute their proportional numbers and kinds to what we call chance. But how false a view is this! Every one has heard that when an American forest is cut down, a very different vegetation springs up; but it has been observed that ancient Indian ruins in the Southern United States, which must formerly have been cleared of trees, now display the same beautiful diversity and proportion of kinds as in the surrounding virgin forest. What a struggle must have gone on during long centuries between the several kinds of trees, each annually scattering its seeds by the thousand; what war between insect and insect—between insects, snails, and other animals with birds and beasts of prey—all striving to increase, all feeding on each other, or on the trees, their seeds and seedlings, or on the other plants which first clothed the ground and thus checked the growth of the trees! Throw up a handful of feathers, and all must fall to the ground according to definite laws; but how simple is the problem where each shall fall compared to that of the action and reaction of the innumerable plants and animals which have determined, in the course of centuries, the proportional numbers and kinds of trees now growing on the old Indian ruins!

(Darwin, C. R. 1869. On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. London: John Murray. 5th edition. Pages 86-87)

This is a fantastic example of Darwin’s breadth of interest and integrated mind. He makes explicit reference to the fact that selection is context dependant (“widely-different checks act on the same species in different districts”). He is explicit about the fact that chance is NOT the operative force in organizing nature (a fact that creationists seem to ignore when they speak of the unlikelihood of a tornado passing through a junkyard creating a Boeing 747 and http://gregladen.com/wordpress/?p=264such hogwash). Continue reading Charles Darwin Bicentennial – A Tangled Bank →