Surely, you think, someone or something must have designed them specifically for their job.
No, says the orthodox evolutionary biologist. Genetic variations occur in any species, all the time. The environment simply selects from those variations the ones that best fit current conditions. If the world cools, the animals with thicker fur survive better and their offspring outnumber the offspring of those with thinner fur, so eventually everyone gets thick fur. If the world starts warming again, same thing happens, only in reverse this time.
Sure, you say, but we’re not talking about things like responding to climate change. We’re talking about very task-specific adaptations to very specialized ways of life. Don’t tell me those come from just chance variation.
I don’t, says the evolutionary biologist. It’s not just chance. It’s chance plus necessity! The necessities of the environment, all the things you have to cope with to survive. These are the things that select from the variations, and that’s all we mean when we talk about “natural selection.”
But wouldn’t that take an awful long . . . ?
Time? Of course, says the evolutionary biologist. But that’s no problem. Evolution has oodles of time! All the time in the world! In fact:
Chance + Necessity + Time = Perfect Fitness. QED.
It’s hardly surprising that a lot of people, people who are by no means the knuckle-walking retards of evolutionist fantasies, have felt dissatisfied with this. Many have been driven into creationism or Intelligent Design precisely because they felt there was something missing from the equation—that to accept it at face value meant as big a leap of faith as believing in some all-powerful agency.
THE EVOLUTION OF EVOLUTION
Think back for a moment to Jean-Baptiste Lamarck, the French naturalist who wrote about evolution fifty years ahead of Darwin. So why do we talk about Darwinism and not Lamarckism? Because Lamarck put all his money on a major evolutionary mechanism that seemed to explain why animals so neatly fitted their environments; only problem was, it turned out to be wrong—at least, wrong in the form in which he stated it. Darwin, on the other hand, hedged his bets; it’s hard to think of any evolutionary theory that you couldn’t support from some quote somewhere in his voluminous writings, including even Lamarckism. So Lamarck, though in many ways ahead of his time, finally lost out.
In the nineteenth century, many people suspected that evolution happened, but nobody knew what made it happen. Lamarck claimed that it happened because acquired characteristics could be inherited—the results of things animals did in their lifetimes could be passed on to their descendants. If they used some part of their bodies more than others, that part would grow and become stronger in their offspring. If they adopted and practiced some new behavior, if say an originally short-necked animal started reaching for the leaves on higher branches, then its children and its children’s children would grow longer and longer necks, and sooner or later, lo and behold, you got giraffes.
When the Austrian monk Gregor Mendel grew sweet peas and showed that what caused them to vary in color from generation to generation had to be something inside the seed, rather than what the plant itself did, the scientific silence was deafening, and Lamarck’s theory still had devoted followers. It wasn’t until early last century that researchers put Darwin and Mendel together, the science of genetics emerged from their union, and the rest, as they say, is history.
But poor old Lamarck and his ideas became History with a big H. How could anyone go on believing that what animals did had any effect on their evolution, once we knew that genes did the trick?
Genes aren’t the only thing, of course, though you could be forgiven for thinking so. In the neo-Darwinian consensus that has dominated biology for a century, animals are just vehicles for their genes. They mate, they breed, they fight for survival, but apart from that they don’t do much; they merely exist as a source of genetic variation from which natural selection can select what is most appropriate under current conditions. And those conditions, of course, are almost always changing. Active environment, hyperactive genes, passive animals—that was the picture neo-Darwinism painted.
In all of this, a vital factor was overlooked.
From time to time, new behaviors appear. (If they didn’t, we would all still be swimming around in the primordial soup.) Where do those behaviors come from? Do the genetic changes come first, then the new behaviors? Certainly not all the time. More often than not, behavior changes first, then the genes change to keep pace with it.
Take weaning, for example—the process by which all infant mammals switch from mother’s milk to their regular species diet (whatever that is). Since there’s no animal Doctor Spock to tell other species how to rear their children, nature has to take care of it. Nature does this by making it so that, at some point in their infancy, mammals cease to be able to digest milk. It’s not a case of fight or switch; it’s a case of switch or starve. We can understand how this came about by thinking what would have happened if it hadn’t.
For other mammals, the only source of milk is mother—they have no domesticated animals to serve as an alternative source. Fine so far, because mother’s milk is one of the most nutritious substances known. If children could keep on drinking it, they surely would. But if they didn’t stop, two things would happen. First, mothers would quickly get exhausted. As things are, weaning gives them a break between bouts of nursing, enabling them to recoup both their energy and their milk supply. But a constantly exhausted mother can’t give her children all the attention they need, and the children would suffer.
Second, very soon there would be two infants (or two sets of infants, for species with multiple births) competing for milk, then three. Very soon the mother would find herself physically incapable of providing sufficient milk for all of them, and in consequence all would suffer from an inadequate diet. Therefore, if there were children who were lactose tolerant beyond the normal age for weaning (that is, children who could digest lactose, the sugar that makes milk indigestible to adults), these would grow up undernourished and unhealthy compared to those who quit the breast early. Even if they didn’t starve to death in childhood they’d have shorter lives and leave fewer children of their own. Thus, over time, lactose intolerant animals would win out and eventually become universal. That’s natural selection at work.
But now for some unnatural selection. If you can drink milk without getting stomach problems, and there are still many in our species who can’t, then you have herdsmen (and herdswomen) somewhere in your family tree. Several thousand years ago some of our ancestors started domesticating animals. In many places they did this where there was little to eat apart from what those animals produced. Their milk, for example; it formed too rich a food source to neglect, and one that, however much you used it, would put no strain at all on your mother.
So people tried drinking it, and it turned out there was a rare mutation on chromosome 2 that in a tiny handful of adults prevented lactose intolerance from developing. (Note that before domestication, this mutation, like most mutations, would have been actively dysfunctional.) These adults drank milk and it made them healthier, just like the milk advertisements say. It gave them a fractional advantage in spreading their genes at the expense of their lactose-intolerant cousins. And, given a few thousand years, a fractional advantage is all it takes for your genes to spread and prosper. Today, 98 percent of Swedes and 88 percent of white Americans are lactose tolerant, while Chinese and Native Americans are respectively 7 and 0 percent tolerant. (Few Chinese and no Native Americans have herding ancestors.)
Now if none of our ancestors had gone for the herding lifestyle, few if any of today’s adults would be able to drink milk. In other words, here’s a genetic change resulting directly from a new thing that people themselves chose to do. Of course what they chose to do didn’t cause the mutation, the evolutionary biologist will remind you—that was pure genetic accident. Perhaps, but the fact remains that, if we hadn’t domesticated animals,
that mutation would have been actively deleterious and would probably have been bred out of the species. Here and in this way, at the very least, humans have taken a hand in their own evolution.
Lamarck had been wrong in his choice of mechanism; genes, not lifetime achievements, are the motor that drives evolution. But his intuition that animals themselves guided their own evolution was dead on target. Because it’s the interaction of genes and behavior that starts the evolutionary motor, and the feedback between genes and behavior that keeps it going. That’s the insight that gave birth to niche construction theory.
HOW NICHE CONSTRUCTION THEORY CHANGED MY LIFE
Barcelona, summer of 2004. I was there for two consecutive gigs: first a weeklong symposium on the evolution of cognition, and then to participate in Barcelona Forum 2004, a mammoth cultural funfair intended to establish the city as the new Paris, the intellectual capital of Western Europe.
One of the other speakers in the symposium was the philosopher Daniel Dennett, probably best known to you from his book Darwin’s Dangerous Idea; we’d last met in Budapest two years before, where we fought for a month over memes (he for them, me against). Another speaker I didn’t know: Marcus Feldman, an Australian working out of Stanford, who was talking on niche construction. I’d never heard of it.
“Do you know this stuff?” I asked Dennett.
“Sure,” he replied. Dan is one of those infuriating people who always hear about everything before you do. “It’s important, too,” he added.
“Come on,” I said. “Everyone knows about beavers.”
“No,” Dennett said, “there’s a lot more to it than that. You should listen up and listen up good.”
I stayed skeptical. Nine new things out of ten in science turn out to be passing fancies, so “skeptical” should be one’s default setting. But apart from his inexplicable infatuation with memes, I have the highest respect for Dan; out of all philosophers, he keeps most on top of every new development in computer science and evolutionary studies.
Came the forum. I was on a panel debating what science could do for world peace. Nothing, I said, except to point out that humans, far from being the gentrified primates that evolutionary psychologists say we are, have chosen a lifestyle much closer to that of ants, and the tensions between our ape nature and our ant circumstances create problems that are probably insoluble. It was actually a niche construction talk, or rather one that badly needed niche construction theory to give it validity and coherence. Of course I didn’t realize that at the time.
On the last day of the panel John Odling-Smee spoke. John, who’s at Oxford University, is, like Feldman, one of the three cofounders of niche construction theory. (The third is Kevin Laland of the University of St. Andrews.) I felt my resistance crumbling. When John finished I asked him a very loaded question, which he answered with grace and skill. We got to talking afterward, and went to lunch together in the hotel we were both staying at, a neo-Japanese monstrosity where the black-robed waiters looked like Buddhist monks. I was starting to get really excited, because I could now see that with this theory a lot of vague ideas that had been floating around my head for a long time might come together and make sense.
Over the next few weeks, John very kindly e-mailed me a slew of articles on niche construction, some for it, some against, and I eagerly read the first and so far the only book on it, Niche Construction: The Neglected Process in Evolution, by Odling-Smee, Laland, and Feldman, which had come out the previous year. And I became hooked. This was one of those ideas that are so beautiful, so stunningly simple, you wonder why nobody ever thought of it before.
WHAT THE THEORY SAYS
Well, that’s not quite fair. Richard Lewontin, Conrad Waddington, and other biologists had emphasized the importance of behavior in evolution. Richard Dawkins, who became one of niche construction’s sharpest critics, wrote a book called The Extended Phenotype that anticipated certain aspects of the theory. Dawkins wanted to modify the concept of phenotype—formerly just the expression of an animal’s genes in terms of its own body shape and skills—to include the artifacts, if any, that the animal constructed. In other words, a beaver’s dam was just as much an expression of beaver genes as a beaver’s tail. But Dawkins’s approach still focused exclusively on genes and what genes did; in his own words, “an animal’s behaviour tends to maximize the survival of the genes ‘for’ that behaviour.” According to the niche constructionists, this was only the beginning of the story.
The basic idea to hold in mind is that animals themselves modify the environments they live in, and that these modified environments, in turn, select for further genetic variations in the animal. So a feedback process begins, a two-way street in which the animal is developing the niche and the niche is developing the animal, until you get the lock-and-key fit between animal and niche that makes people say, “But there must be a designer!” Animals aren’t just passive vehicles for their genes; they play an active role in designing their own destiny.
So what exactly is a niche, anyway?
According to Eugene Odum, author of Fundamentals of Ecology, “the ecological niche of an organism depends not only on where it lives but also on what it does. By analogy, it may be said that the habitat is the organism’s ‘address,’ and the niche is its ‘profession,’ biologically speaking.” In fact we can distinguish not just two but three essential components of a niche:
• Habitat: a particular type of environment that can be macro (savanna, rain forest, marsh, mountain, tundra . . . ) and/or micro (topsoil, tree bark, pond scum, nest, burrow, mound . . . ).
• Nourishment: a particular type of food (grass, meat, insects, honey, microorganisms, fruit, blood . . . or some combination of these and/or other things).
• Means: a particular way of obtaining that food (foraging, scavenging, stalking, pack hunting, ambushing, sieving, digging . . . ).
Thus the hyena niche consists in living on open savannas, eating meat, and scavenging or hunting in packs. The niche for baleen whales consists in living in the open ocean and eating marine microorganisms obtained by sieving seawater. The frog niche consists in living in ponds or swamps and eating insects for which the frog lies in wait.
People haven’t often thought of niches as being actively constructed. They’ve tended to think of them as ready-made, just waiting for some animal to step into them, and have regarded beavers, for example, as quaint exceptions to this rule. Not so; the authors of Niche Construction list hundreds of species that, to some degree or other, engineer their own niches. Beavers, ant species like leaf-cutters that build underground fungus farms, and earthworms are just some of the more dramatic cases.
Take earthworms, for instance.
Darwin loved earthworms. He studied them perhaps more than any other organism. His last published book was about worms. If worms had given him the same depth of insight that Galapagos finches did, evolutionary biology might have developed very differently. But they couldn’t have. To understand what makes earthworms special, you have to already know something about modern, gene-centered versions of evolutionary theory.
They’re called earthworms, but they weren’t always. They began life as waterworms. But just as ancestors of whales and dolphins went from land to water, so these worms made the reverse journey. Only they didn’t do what whales and dolphins did, what evolutionary science says they should have done—simply and straightforwardly adapt themselves to the new environment. Instead, at least in part, they adapted the new environment to themselves.
Makes sense when you think about it. There’s not much you can do with water. But earth is malleable; you can mine it, shape it, even eat it if you have the right kind of stomach. So earthworms-to-be set about changing the land.
They didn’t change their kidneys. They didn’t change their production of urine. (Water-dwelling organisms put out more urine than land dwellers, mostly to get rid of excess salt.) They didn’t change any of their other bodily forms or functions in ways that so drasti
c a transition might lead you to expect. Instead, they transformed the ground itself. They started by exuding quantities of mucus that softened the ground and made it slippery so they could dig and navigate a system of tunnels. Then they dragged bits of decaying vegetation into these tunnels and mixed it with inorganic material and ate the mix. What they then excreted—known as “worm casts”—is so rich in minerals and fine in texture that avid gardeners, my wife included, keep round metal drums full of worms, feed them the household scraps, and reap the richest compost known. (What’s more, the brown liquid that collects in the bottom of the drum, in which, Yvonne says, “they love to take a swim,” makes a fantastic organic fertilizer.)
But wait, those are domesticated worms. Wild worms have a harder row to hoe, but they’re not all that different. Stick a spade into hard compacted earth that hasn’t ever grown much in the way of plants and you probably won’t see any worms. Put the same spade into loose crumbly loam and you’ll turn up a worm or two almost every time. You might think, oh well, that’s just because I’ve dug and fertilized that part of the garden. Maybe, but there was rich loamy soil long before there were human gardeners, because generations of worms had worked on it, breaking it up, enriching it with their casts. It was a mutual process, niche and organism changing together—worms putting out more mucus, getting to digest more varied substances, while the earth around them grew ever richer in nutrients and easier for them to tunnel. These mutually reinforcing processes have gone on for countless worm generations, fitting worms to earth, earth to worms, and incidentally making the world a happier place for insects, plants, gardeners, and other organisms that benefit from enriched soils.
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