Friday, November 18, 2011

The Garden of Eden in Ancient Oceans

There never was a Garden of Eden, but there was, perhaps, a Garden of Ediacara. (See the book by Mark McMenamin by this title.) Ediacaran organisms (named after the place in Australia where their fossils were first recognized) were blob-like creatures that lived in the sea about 600 million years ago. In this innocent garden, there were no predators. As soon as the predators evolved, it seems that the Ediacarans all got eaten.

It is easy to see what an attraction it is to an animal to eat other animals instead of eating plants. Animal flesh is much more nutritious than leaf tissues. Leaf tissues have a lot of water and fiber, while animal flesh is a highly concentrated source of protein and fat—even more so than seeds, which are rare compared to leaves. One might even say that many herbivores would be carnivores if they could. Live squirrels sometimes nibble on roadkill squirrels, and deer sometimes eat captive chicks. Natural selection has favored squirrels that are really good at finding and eating nuts and deer that are good at browsing. They are not very good predators. But if a nice dinner of meat is presented to them, who are they to turn it down? Nonhuman vegetarians, like most human vegetarians, are tempted by meat.

Predators are usually swift, intelligent, and have good eyesight. Each of these adaptations allows them to find and catch prey more effectively. It is true that prey would benefit from having these adaptations as well. Swiftness, intelligence, and sharp eyesight would allow prey animals to escape predators. But in most cases, predators are superior in these respects, and natural selection has favored prey that can see only well enough, and are only smart and fast enough, to hide. By spending less of their time and energy on defense against predators, the prey animals that survive animals can produce more offspring and find more food. Predators generally produce fewer offspring than prey animals do. Sometimes, prey animals are poisonous, and predators evolve the ability to tolerate the poisons.

Prey defenses do not have to be perfect. Some defenses appear to be almost perfect: some mantises look just like sticks or leaves, enough to fool even naturalists walking through the woods. But even a little bit of camouflage is better than none at all. I saw a cartoon once in which a lion told a zebra, “You call that camouflage?” Black stripes on white (or white on black, I forget which) honestly do not look like the grasses of the African savanna. Except, that is, at nightfall, which is when the lions are most active. Zebras are blatantly obvious in the middle of the day, but that is when the lions are dozing. Predator adaptations need not be perfect either. As I write, our cat seems unable to tell the difference between my computer mouse and a real one. Natural selection has not favored the evolution of sufficient intelligence in cats to allow them to distinguish an actual mouse from other objects. Even though computer mice have not been part of the evolutionary experience of cats, an extremely intelligent cat should be able to tell that a bright green object without legs is not a mouse. But cats, such as the hundred million feral cats in the United States, are intelligent enough for their own purposes. To have greater intelligence, a bigger brain, would be a waste of resources for them.

Some prey animals have social defenses. They form large herds in which each animal looks out for the safety of the others, to a certain extent. Lions can subdue an individual zebra or wildebeest, but when confronted by a flood of hooves and confusing black and white stripes, where to begin?

The Garden of Eden was, by tradition, filled with vegetarian animals. Vegetarian tigers and lions. As you can see, such a Garden could not have persisted for very long; inevitably, some of the animals would have evolved into predators. There will never be a world in which, as in the vision of the prophet Isaiah, the lion lies down with the lamb. The natural world is not like the Bambi movie, with Friend Owl imparting wisdom to little Thumper. In the real world, Friend Owl would be eating Thumper.

This is coevolution: natural selection favors prey that can escape or hide from predators, or even fight them off, but not so much that they cannot grow, and predators that can catch the prey, but not so much that they divert too much energy away from their own metabolism, movement, and growth.

This entry is adapted from my book Life of Earth: Portrait of a Beautiful, Middle-Aged, Stressed-Out World, published earlier this year by Prometheus Books.

Thursday, November 10, 2011

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!

Friday, November 4, 2011

Darwin Celebrates Halloween

Last Monday was Halloween (or, in the traditional spelling, Hallowe’en, or Hallowed Evening). I taught my evolution class that morning. I wore a T-shirt with a skull on it, with the word “Evolution” over it. Evolution is the name of a little store in the Soho section of New York City which sells items that are vaguely connected with evolution (e.g., tarantulas in plastic).

I then put on a zombie mask and screamed out to the class, “Brains! Brains! BRAINS! BRAINS! I’m Charles Darwin and I’m going to eat your brains and your children’s brains and turn you all into atheists!”

I then removed the mask and explained that Darwin was not a zombie, and that I had no intention of turning anybody into an atheist. I said something like this. “Now, if your religion requires you to believe things that are scientifically disprovable, then I will have to tell you that you are mistaken. But science cannot tell you whether or not there is a purpose behind the universe, or even if there are other universes, or whether this purpose is a personal God. Many scientists believe in God, without any contradiction with their roles as scientists.”

Then I told them about Darwin’s American friend, the Harvard botanist Asa Gray, who was the chief defender of Darwinian evolution in America, but who was as traditional and orthodox a Christian as you could hope to find. A Sunday school teacher, no less. Darwin explained in a letter to Gray how much he regretted that he could not agree with Gray on a religious view. Darwin wrote to Gray, “With respect to the theological view of the question. This is always painful to me. I am bewildered. I had no intention to write atheistically. But I own that I cannot see as plainly as others do, and as I should wish to do, evidence of design and beneficence on all sides of us.”

I then told them about the correspondence I have been maintaining with a prisoner in California. He first wrote to me a couple of years ago when he read my review of an evolution book. He must already have been pursuing an understanding of evolution, because he got my name from a book review I wrote for the National Center for Science Education Reports. He has written to me with many questions, and I have sent answers back to him. I have also sent him paper printouts of things I have written (hardcover books are not allowed in prison mail delivery).

At one point, the prisoner wrote to me about becoming an atheist and the freedom of thought that this allowed him to have. I wrote back to him recently, explaining that atheism was not necessary in order to accept science in general or evolution in particular, and that many scientists are religious. I do not want to lead anyone to atheism. In this way, I am doing exactly what Darwin did. I have not yet received a reply from the prisoner.

I used Halloween as a humorous opportunity to bring up a discussion of this important topic.

Don't miss the YouTube video that I have posted about Darwin and zombies!