Why You Are Not a Prairie Dog: More Insights from Loren Eiseley

I have recently been reading essays by Loren Eiseley, a paleontologist of the middle twentieth century. His books, such as The Firmament of Time and The Immense Journey, were considered epics of popular science writing at the time they were published. Many of his essays are very well-written, and I recommend him to any of you who like classic nature writing.

One of his essays, The Slit, is about a time in which he went down into a cavern and dug out a mammal skull from shortly after the extinction of the dinosaurs. Primates, the order to which humans and other apes belong, started to diversify right after the dinosaurs became extinct. One of the directions that they diversified was into arboreal forms, living in the trees. And that is where most of them still are, except for baboons and people. Another direction was to live by burrowing in the ground out in the newly-spreading grasslands. These primates eventually became extinct. Why? It was probably because of another order of mammals that was evolving and diversifying at the same time: rodents, which includes prairie dogs and ground squirrels. [Here is a photo I took of a prairie dog in the Badlands of South Dakota in 2000.]

Very early in the Cenozoic Era, it was not clear which direction mammalian evolution might take. Out in open prairies, both primates and rodents diversified. But the rodents were more successful, driving the burrowing primates to extinction. Had things ended up just slightly differently, primates might have been primarily burrowing animals, rather than leaping around in trees. And humans might not have evolved.

Another insight I got from reading Eiseley was a possible contributing factor to human intelligence. Our big brains require a lot of oxygen, therefore a lot of blood vessels. Why did our lineage, starting with the amphibians, have such well-oxygenated brains? The answer might be that amphibians evolved not just in shallow water, not just in shallow fresh water, but in shallow fresh anoxic water, so that extra blood vessels were required to keep even their small brains alive. It was this extra vascularization that made the evolution of intelligent terrestrial vertebrates possible.

To me, this was an excellent example of how the slightest change in the course of events can make a huge difference in the evolutionary outcome.

As the Case May Be: The Subjunctive Mood and Human Evolution

Humans are the only species with true language. Monkeys can respond differently to different calls, and chimps can learn a few symbols. But to have true language, you have to have vivid imagination, which is unique to humans.

Language can communicate situations that do not yet exist—the future tense. In English, we could say if he will go. In French, s’il ira. But even more than this, language can communicate an alternate reality that is different from the one you are experiencing. If he were to go implies that he is not going to go. In French, s’il aille. This is the subjunctive, as it were. You can even have a past subjunctive: if he had gone, s’il soit allé. Language students hate learning subjunctives, but they are a marvel of intellect. That does not mean, of course, that you have to like them.

Organisms have lots of ways of responding to their surroundings. The ancestors of vertebrates specialized on intelligence as their mode of response. As explained in an earlier essay, intelligence is expensive. In humans, natural selection favored larger brains in a runaway spiral of greater and greater intelligence. It is expensive. Along the way in human evolution, a threshold was crossed into the kind of self-awareness that permitted the oft-maligned subjunctive mood.

Darwin Had a Sense of Humour

Anyone who has read the Origin of Species would say that it is clearly and beautifully written, with occasional bursts of beauty, even though it is verbose and formal like all Victorian writing. But funny? I wasn’t expecting Darwin’s writing to be funny. But there is a passage in Descent of Man that is funnier than anything I have read by other Victorian writers.

Darwin begins the Descent of Man by presenting evidence of the close similarity of humans and apes. He mentions several anatomical characteristics in which humans and apes hardly differ at all. In this book and in the Expression of Emotions, Darwin notes many behavioral similarities (gestures, facial expressions, etc.) that humans share with apes. But Darwin had very little to say about physiological similarities, because so little was known about physiology at the time. Enzymes? Genes? How nerves work? None of this was known.

Darwin did the next best thing. He presented evidence that humans and other apes have similar physiological reactions to chemicals. One of the chemicals that he chose was alcohol. Here is a really funny passage, in which Darwin explains not only that monkeys can get drunk, but even have similar responses the next day (Chapter 1):

“Many kinds of monkeys have a strong taste for tea, coffee, and spirituous liquors: they will also, as I have myself seen, smoke tobacco with pleasure. Brehm asserts that the natives of north-eastern Africa catch the wild baboons by exposing vessels with strong beer, by which they are made drunk. He has seen some of these animals, which he kept in confinement, in this state; and he gives a laughable account of their behavior and strange grimaces. On the following morning they were very cross and dismal; they held their aching heads with both hands, and wore a most pitiable expression: when beer or wine was offered them, they turned away with disgust, but relished the juice of lemons. An American monkey…after getting drunk on brandy, would never touch it again, and thus was wiser than many men. These trifling facts prove how similar the nerves of taste must be in monkeys and man, and how similarly the whole nervous system is affected.”

A passage that is both funny and scientifically significant. Way to go, Charley!