First off, the other day I mentioned that I would say something about my honour’s work sooner or later. I will, and, considering how excited I am about the upcoming Paul Nelson day, I’ll post something about it tomorrow*.
This is also a pretty significant chapter: there is a tremendous discussion of the biogeography of both extant and extinct species, and several instances of what are probably sexual selection, though the utility is in neither case apparent to Darwin.
Darwin first discusses bizcacha a rodent similar to an agouti. Bizcachas have never been seen east of the Uruguay River, even though the vegetation there would be well suited to their tastes. They have a habit of gathering hard objects and placing them near their burrows, but not in a way that might be employed for self-defense. He compares this to an Australian bowerbird, Chlamydera maculata. The purpose of even the bowerbird’s collections have not yet been identified: “…the Calodera maculata, which makes an elegant vaulted passage of twigs for playing in, and which collects near the spot, land and sea shells, bones and the feathers of birds, especially brightly coloured ones.” Darwin does not attempt to speculate as to the bizcacha’s purpose in accumulating these objects. The locals in both locations will, when they lose some item, will begin their searches near the nests of these creatures – often quite successfully.
Darwin is bedridden for a few days with a headache, and describes some of the local “healing” modalities. “One of the least nasty ways is to kill and cut open two puppies and bind them on each side of a broken limb.” Many others, are, apparently, too gruesome to describe – a point I’d rather not think about too long. Funny thing, ancient wisdom, isn’t it?
He spends a few days fossil hunting around the Parana River, where he finds shark’s teeth, shells, as well as the teeth of Toxodon and Mastodons, the armour of an armidillo-like creature, and a horse’s tooth. With this last one, he takes great care to note the geological layer in which the tooth was found. Unlike most horses, this species had curved teeth. Professor Owen classifies it, along with another fossil discovered by Charles Lyell in North America, as Equus curvidens.
Certainly it is a marvellous fact in the history of the Mammalia, that in South America a native horse should have lived and disappeared, to be succeeded in after-ages by the countless herds descended from the few introduced with the Spanish colonists!
Comparing and contrasting the mammal fauna of North and South America, Darwin divides them (following the work of Lichtenstein, Swainson, Erichson and Richardson, according to a footnote) at a line of 20°N latitude through Mexico. A few species have passed through this barrier, but generally there are distinct species on each side.
|North America||South America|
However, even in recent (geologically) times, in North America there lived a mastodon, horse, and three genera of Edentata – the Megatherium, Megalonyx, and Mylodon, all of which Darwin has already discovered fossils of in South America. South America had also previously been inhabited by a hollow-horned ruminant, apparently, but no further details are forthcoming.
Hence it is evident that North and South America, in having within a late geological period these several genera in common, were much more closely related in the character of their terrestrial inhabitants than they now are. The more I reflect on this case, the more interesting it appears: I know of no other instance where we can almost mark the period and splitting up of one great region into two well-characterized geological provinces. The geologist, who is fully impressed with the vast oscillations of level which have affected the earth’s crust within late eriods will not fear to speculate on the recent elevation of the Mexican platform, or, more probably, on the recent submergence of land in the West Indian Archipelago, as the cause of the present zoological separation of North and South America. The South American character of West Indian mammals seems to indicate that this archipelago was formerly united to the southern continent, and that it has subsequently been an area of subsidence.
When America, and especially North America, possessed its elephants, mastodons, horse,and hollow-horned ruminants, it was much more closely related in its zoological characters to the temperate parts of Europe and Asia than it now is. As the remains of these genera are found on both sides of Behring’s Straits and on the plains of Siberia, we are led to look to the north-western side of North America as the former point of communication between the Old and so-called New World. And as so many species, both living and extinct, of these same genera inhabit and have inhabited the Old World, it seems most probable that the North American elephants, mastodons, horse, and hollow-horned ruminants migrated, on land since submerged near Behring’s Straits, from Siberia into North America, and thence, on land since submerged in the West Indies, into South America, where for a time they mingled with the forms characteristic of that southern continent, and have since become extinct.
This seems to me a passage of no small importance. Some of these ideas have not stood the test of time, but it is nonetheless a useful guide to Darwin’s thinking. One thing I’ve been trying to figure out for some time is how far along his evolutionary thinking was at the time he was writing this, and I’ve been thinking it would be useful to read a biography of Darwin (or perhaps his autobiography). This passage leads me to think that the concepts were not well-developed (or perhaps he’s just being chronological about his thinking – certainly he did not have any conception of evolution at this stage in the voyage). Nonetheless, we can see, perhaps to a limited extent, that species are, at least, not fixed – they can… “mingle”… and produce something distinct. I’m even tempted to perhaps look into Lyell’s Principles of Geology, for some context on the then-radical concepts in natural history.
There are many islands in the Parana River, inhabited by capybaras and jaguars. These are dangerous man-eaters: they mostly eat the capybara, but sometimes attack loggers, and, if their islands are flooded, will board ships or enter towns in search of food.
The scissor-beak has a flat beak, with the lower bill 1.5″ longer than the upper, and skims the surface for prey. Darwin also discusses a catfish, and the large population of mosquitoes that they encounter.
He meets a friendly old Spaniard who figures that the battle of Trafalgar has only won by England because all the Spanish captains had been bribed. “It struck me as rather characteristic that this man should prefer his countrymen be thought the worst of traitors, rather than unskillful or cowardly.”
The country is, by Darwin’s reckoning, somewhat under-utilised, a very fertile country with a river perfect for cargo and communication. “How different would have been the aspect of this river if English colonists had by good fortune first sailed up the Plata! What noble towns would now have occupied its shores!”
Darwin is hurrying to reach the Beagle before it sails again, but is delayed for nearly a fortnight in Las Conchas due to a rebellion attempting to give General Rosas the power he wants. Rosas had been elected governor a year earlier, but had wanted extra powers. He was refused these, and so was leading rebellions and demonstrating that no other government other than one headed by him could maintain such powers: and, indeed, there had been fifteen regime changes in the past nine months. His current opinion on General Rosas seem very different than those of a few chapters ago, so perhaps this is a chronological description of his thinking (as wouldn’t be entirely unexpected for a journal).
Next time: Banda Oriental and Patagonia. Or maybe something on my honour’s research. But I wouldn’t count on it.