By Jerry Sullivan
Some years ago I interviewed a biologist who had been hired by the Wisconsin Department of Natural Resources to monitor the three packs of timber wolves that then lived in the state. One of his study methods involved trapping wolves and outfitting them with radio collars that enabled him to track their movements.
Unfortunately for his project, the wolves in one pack learned to remove the collars. They had to work together to do this. No wolf could remove the collar from its own neck. But a pack mate could chew through the straps and buckles and release its fellow. Only one pack learned this trick. The wolves in the other two packs stayed trackable.
I was reminded of this story recently while reading Tribe of the Tiger by Elizabeth Marshall Thomas. Thomas’s subject is cats, the whole family from tabbies to the man-eating Bengals of the Ganges Delta. Among her stories is an account of the relationship that once obtained between the Bushmen and the lions of the Kalahari Desert in southwestern Africa. Thomas’s parents were anthropologists who studied the Bushmen, and she spent several years with them in the Kalahari in the 50s.
At the time almost no outsiders came anywhere near the Kalahari, so nobody interfered with the deal the Bushmen and the lions had worked out. The Bushmen had no weapons of much use against a lion. They relied on arrows dipped in a slow-acting poison for hunting, and anybody facing a charging lion needs a poison that acts really fast.
Despite their apparent defenselessness, the Bushmen were never attacked by lions. The two tribes of hunters–feline and primate–lived side by side in an atmosphere of mutual respect and nonaggression. Thomas accounts for this truce partly in ecological terms. Like many potential competitors, the lions and the humans divided their habitat to avoid conflict. The lions hunted at night; the people hunted during the day. The lions visited the water hole late in the day; the humans went there early.
But there was more to it than that. There was also in the cultures of both parties a mutual understanding that they would respectfully avoid one another. What should we do, the Marshalls asked the Bushmen, if we come face-to-face with a lion? The correct technique, according to the Bushmen, was to walk at an oblique angle past the animal. Keep it in view out of the corner of your eye, but don’t stare. Walk at a steady pace, but not too fast.
The first time Elizabeth Marshall Thomas saw this technique applied, it was not by a human. She and her brother came face-to-face with a magnificent male lion. Both people were so thunderstruck by the encounter that they could do nothing but stand and stare. The lion proceeded to walk past them at an oblique angle–keeping them in view out of the corner of his eye. Thomas felt reassured by the lion’s actions. Good manners, she writes, are always reassuring. They put others at ease.
We can only speculate about how this truce developed and stand in awe of the sheer courage of the people who began it. And we can note that it arose in a situation of long-standing stability. People and lions have been living together in the Kalahari for close to 100,000 years.
The stable relationship has ended during the past 40 years. Settlers have moved in with cattle, and lions do eat cattle. Fires have been suppressed, so brush is taking over the grasslands. And the Bushmen have been removed from their ancestral lands.
The removal came about because the land was declared a park. The people who run the park are conscientious representatives of Western culture. It is as obvious to them as it is to us that humans have no place in nature except as occasional visitors–preferably in Land Rovers.
With the people gone, the park managers turned their attention to the lions. There were far too many of them, and they were in all the wrong places. So a massive program of culling and relocation began. The cultures of humans and lions and the mutual culture of humans and lions living together were broken. Now Kalahari lions attack people, and park workers stay close to their Land Rovers.
All of this was on my mind when I began reading The Beak of the Finch by Jonathan Weiner. This remarkable book is mainly about the long-term research project being carried out by Peter and Rosemary Grant and several generations of graduate students on a tiny island in the Galapagos called Daphne Major. The objects of the study are several species of the genus Geospiza, the small birds of the Galapagos that will forever be lumped together as Darwin’s finches.
It’s just legend that these are the birds that inspired the essential insight that led to the writing of On the Origin of Species, but there is no doubt that the whole flora and fauna of the Galapagos played a major role in shaping Darwin’s thinking. And these birds do provide an excellent example of the sort of evolutionary development called adaptive radiation.
We can reconstruct a history that begins with one windblown flock of finches landing on the Galapagos and finding whole islands full of rich opportunities. As time went by, the birds began to specialize. Some became ground feeders; others fed in the cactus branches. Some specialized in small seeds; others went after larger seeds.
Through the generations their ways of life changed them. Natural selection favored, for example, heavier beaks for seedeaters and longer beaks for those birds that probed inside cactus flowers for nectar. Birds that bred with others like themselves produced young that carried these trends further. Beaks got bigger or longer because the birds that carried these adaptations the furthest were the most successful and the most likely to pass along their genes.
Darwin thought this process, the process of natural selection, took a very long time. No human could observe it, because a human life span is just too short to see significant change. One of the consistent themes of creationists is that Darwin’s ideas are just as much a matter of faith as the Book of Genesis. We didn’t witness creation, and we can’t witness natural selection.
But Peter and Rosemary Grant have witnessed natural selection, and their data allow the rest of us to see it too. Islands as isolated as the Galapagos are ideal laboratories for ecologists. Only a few species are present, and they are mostly isolated. The Grants have been able to band almost every finch on Daphne Major for the past 20-some generations. They know the size of everyone’s beak and the span of everyone’s wings. And they have witnessed two intense selection events that produced a measurable change in the finches of Daphne Major in just one generation.
The first of these was an intense drought. Between March 1976 and December 1977 the finch population on the island dropped from 1,400 birds to 300. The carnage was not random. Among the seed-eating finches, it was the birds with the biggest beaks, the birds capable of handling hard seeds that smaller birds couldn’t eat, that survived. The new, reduced breeding population of Geospiza fortis, for example, was an average of 5 to 6 percent larger than the predrought population. Their beaks were a half a millimeter longer and deeper than the predrought average. Small differences, but enough to separate those that can crack the big seeds from those that cannot.
A second selection event, a season of abnormally heavy rainfall, pushed the population in the opposite direction, favoring small birds accustomed to eating small seeds. We can imagine the status quo on the Galapagos being maintained by such alterations. A long stretch of drought or an extended period of heavy rainfall could send the whole process into a permanent change.
The sight of natural selection in action is beautiful, and Weiner tells the story very well. But the most fascinating story in The Beak of the Finch is about the finches of the tiny island of Cocos. Cocos lies north of the Galapagos, right on the equator. It rains all the time there, and the entire island is covered with dense rain forest.
Rain forests are filled with niches for a great variety of birds, but Cocos is so small that the kind of isolation that might carry a selection episode through to the creation of a new species hasn’t happened. Instead the birds, all of the same species, have learned to exploit their varied environment through culture. Individuals may glean insects from living leaves or from branches. They may sip nectar from flowers. They may specialize in dead leaves. Whatever their chosen method of getting food, they stay with it, just as a human farmer sticks to farming and a programmer sticks to computers. Young birds are regularly observed following their elders around, watching and clumsily imitating them.
It is a short jump from generalized birds that pass along vital skills through culture to the well-known featherless biped that does the same thing. Culture, it seems, is not the uniquely human thing they told me about in Anthropology 101. It is something we share with many other animals. The difference between our culture and theirs is that ours is so dense, so multilayered, that we can live completely inside it. The selection pressures we face as individuals are almost entirely social, not natural. To deny this is to make the same mistake the social Darwinists made and declare differences in wealth or power to be products of nature and nature’s laws–as if culture were a transparent medium that let natural forces through without hindrance.
You can make a case for the idea that natural selection does operate at the level of culture, that civilizations from Mesopotamia to Mesa Verde have declined when the methods they used to make a living conflicted with natural forces. The final section of The Beak of the Finch is about antibiotics and pesticides and the endlessly inventive ways that insects, bacteria, protozoans, and viruses have evolved to protect themselves against these poisons.
No crop is more dependent on pesticides than cotton, and Weiner points out the choice irony that most cotton produced in the United States is grown in states where hostility to the ideas of Darwin is widespread and powerful. While the legislatures look for ways to keep evolution out of the schools, the cotton farmers spray more and more poisons and are constantly surprised to find that the chemists can’t come up with anything more than a series of stopgaps. And even the chemists, supposedly trained scientists, imagine that someday they will find a poison that natural selection can’t defeat. We declare nature to be a servant or an enemy, insist that we properly have dominion over it. And then wonder if it is safe to leave the Land Rover.