Intelligence in Nature Part 2

One day, the sun came out and the snow began to thaw. I went for a run and soaked up the rays and warmth with gusto. As I made my way along the trail up in the pastures next to the woods, my eyes caught a strange sight. A large pink earthworm was crawling very slowly across the snow, coming from an earth bank exposed to the sun. I stopped to observe it for a while. Like me, it had made its way out into the first warmth of the year and appeared to be going somewhere.

Chapter 5.

INSECT MINDS.

It was mid-May, and spring was turning to summer. I made a beeline for the South of France. Coming from the Swiss hills, I felt hot for the first time that year. I had an appointment at the University of Toulouse with Martin Giurfa, a scientist who had recently demonstrated that bees can handle abstract concepts.

The work by Giurfa and his colleagues had caught my attention in a scientific journal. They reported on an experiment in which they exposed honeybees to a simple Y-shaped maze. The entrance to the maze was marked with a particular symbol, such as the color blue. A bee flying through the entrance encountered a branching pathway, or "decision chamber," where it could choose between paths. One path was marked with the color blue, the other with the color yellow. Bees that followed the blue-marked path discovered at its end a vial filled with sugared solution. Bees that took the yellow path received no reward. The bees soon learned that sugar lay at the end of the route marked with the same symbol as the one marking the outside entrance. "Same" equals "sugar," in other words. In a subsequent experiment, the opening to the maze was marked by a different symbol, such as horizontal dark lines. In that case, on entering the decision chamber, the bees reencountered the two pathways, which were marked this time not with colors but with lines"vertical lines on one path, horizontal lines on the other. The bees pa.s.sed with flying colors, heading straight for the pattern that matched what they saw at the entrance. Other experiments revealed that the bees could also transfer their knowledge across the senses: Bees that learned about sameness by matching odors were able to apply the concept to visual signs. Though bees have brains the size of pinheads, they can master abstract rules.

This research falsified the notion that "brutes abstract not." It also showed that small brains do not hinder thought. I felt moved to meet the person behind this research and hear his point of view.

The University of Toulouse has a sprawling campus. Despite the signs and pathways, it took me half an hour to find the Laboratoire d"Ethologie et de Cognition Animale. It was located in a four-story building that was being renovated. As I walked in, drills resonated from the floors above.

Martin Giurfa had recently been chosen by France"s National Center for Scientific Research (CNRS) to head their new center for the study of animal cognition. We had not met previously or spoken on the phone and had only communicated by electronic mail. As I knocked on his door, I considered the possibility that he might wear a white lab coat and speak with detachment.

Instead I found a youngish-looking man sitting in front of a computer at a comfortable desk, wearing a green-checked s.h.i.+rt with short sleeves. The room was filled with plants, and the blinds were down to fend off the sunlight. Giurfa wore wire-rimmed gla.s.ses, and his hair was dark and short. He smiled and invited me to sit down in the chair next to his desk. He spoke English with an indeterminate accent. I asked where he was from. He said that he was born in Argentina and that his family had come from Italy.

As a cultural hybrid, I felt at ease with Giurfa. I was curious to know how he had come to develop an interest in biology. "Since I can remember, I have loved animals," he replied. "I was always fascinated by the observation and the magic of the living machine. But I have just made a big mistake: I used the term machine to describe living organisms. That is exactly the opposite of what I think. In fact they are not machines. But I was always fascinated by looking at the living organism, from the point of view of the exterior observer, seeing how it moves, takes decisions, and so on. It was always fascinating for me how a wasp decides to go here and not there, how a wasp finds its way home and identifies the nest, how a bee forages from flower to flower, always going from the flowers of one species to the same species." As a child, Giurfa kept different animals as pets, including insects, water snakes, and a boa constrictor"much to his mother"s dismay.

Giurfa explained that he had referred to bees as "machines" because that was how he used to think about them in the past. But the more he understood how animals make decisions and learn, the more he had to admit that they do not act mechanically. His view started to change in 1990, when he went to Berlin and began working in a leading neurobiology inst.i.tute, alongside sixty colleagues from different fields of science who were all studying memory and learning in honeybees. It soon dawned on him that bees learn in an intelligent way. For example, their capacity to navigate surpa.s.ses our own: "If I take you to a distant part of the campus," he said, "and release you there, you won"t find your way easily back here. But bees can. How they do it is the question. This is why I started to think about cognition in invertebrates, which, of course, at the time, was considered a kind of contradiction in terms. People said, "You are absolutely crazy for raising this kind of question. How could you think that invertebrates could have this kind of intelligent behavior?" That is what people were saying to me."

"What did you make of that resistance?"

"I simply didn"t care about it. That was an advantage in Berlin; you had intellectual freedom to raise questions and perform research work."

I wanted to know why some of his colleagues were so opposed to studying cognition in invertebrates. "Basically," he said, "it was the dominating view, that you can find even now in some people, for instance in researchers working with vertebrates. They still think that invertebrates are small robots, that they are simple machines, reflex machines, you know, like Pavlov machines, or Skinner machines. Simply like hitting a hammer on your knee and having a jerk reaction. They say that invertebrates have to be simple like that."

Though Giurfa was critical of the robotic view of insects, he admitted that it had helped advance the study of insect movements and behaviors. "Considering insects as simple robots has, for instance, stimulated the creation of machines like the Mars explorer, which was inspired by how insects move their legs and so on. This point of view is of course short minded, if you will, but at least it had this positive aspect."

Someone knocked on the door, interrupting the conversation. Giurfa had a brief exchange in French with a colleague, and I noticed that he spoke with greater fluency than in English. Once he was done, I renewed the conversation in French and we continued in that language. I asked whether there had been resistance to his recent work on the capacity of bees to handle abstract concepts. He said he was confident that the experiments were well conducted and that the results, which were published in the journal Nature, could not be attacked scientifically. But he did mention resistance from a group of researchers at a nearby center for the study of primate cognition. They contacted Giurfa to say that they had tested monkeys on the same task and found that certain species could not do it; therefore, they did not believe it was possible bees could. Giurfa said this kind of reaction occurred less and less frequently.

In his view, when animals are found not to accomplish a given task, this is not proof of their stupidity. "In most cases, the problem lies with the person conducting the experiment and involves incapacity in the researcher to develop experiments that pose the problem correctly and allow one to answer it properly. If you will, a negative result shows nothing, in the final a.n.a.lysis. A positive result shows something. But when an animal cannot do something, the question remains: Is it incapable of doing it or have I not been clever enough in my research concepts and experimental design?"

"So, would you say that the problem for the moment is not that nature lacks intelligence but that researchers studying it do?" I asked.

"That is one of the problems, certainly. I think we are a long way from having made a kind of mental jump which would allow us to ask certain questions."

I had read several recent books that discounted the intelligence of individual insects, referring instead to "swarm intelligence." The idea seemed to be that bees were mindless robots programmed according to a series of simple rules, and that intelligent behavior emerged from the interactions of the mindless parts. "Emergence" was a concept that was used to explain how "dimwitted" individuals could appear to act intelligently. I asked Giurfa what he thought about "swarm intelligence" and "emergence."

He replied that these concepts could explain some behaviors, but not all, and that it was important to distinguish between group behavior and the intelligence of the individual. "All these studies on emergent properties are certainly interesting, and they are a good challenge for me. I like these studies because they make me rethink my own research from another perspective." He said it was important not to take his own point of view too far by claiming, for example, that bees are capable of the highest and most flexible forms of learning. In fact, bees sometimes behave stupidly. If placed in a maze with a gla.s.s cover, for example, they perform as well as rats up to the point of reaching the food reward, but they are incapable of turning around and going back to where they have come from. Once bees eat, they are rigidly programmed to fly upward. Bees in a gla.s.s-covered maze bang against the gla.s.s cover, trying to gain alt.i.tude, until they die. They are programmed according to a simple rule: To get back to the hive, first go upward, to where light intensity is greatest, toward the sky. So, Giurfa said, it is important to avoid exaggerating the plasticity of bee intelligence. Both principles operate: There are simple rules and emergent properties on the one hand, and plastic cognition on the other. "That"s why it"s a challenge, because it obliges me to think about the problems in my system from another perspective as well."

Scientists often use the concept of "instinct" when explaining the capacities of animals. I asked Giurfa if he found it useful in his work. He said that he had started his work in Berlin by studying a question related to bee instinct, looking into whether or not bees have information encoded in their brains when they take their first exploratory flight. Giurfa built a large apiary containing a small beehive in which all external conditions are controlled and went on to demonstrate that bees spontaneously prefer certain colors, in particular very intense blue and yellow. These colors correspond to the flowers richest in nectar. So instinct exists, Giurfa said, and is a useful concept. But Giurfa also found that bees can modify their instinct according to what they learn about the world. In the controlled environment he constructed, Giurfa arranged for pollen to be a.s.sociated with other colors and found that bees can modify their color instincts. "We see the incredible plasticity of the system," he said. "This means that they go into nature equipped with instinctive information, which is not rigid, and which they can forget or put aside on the basis of personal experience, meaning to say on the basis of learning."

A loud hammering echoed through the ceiling. Upstairs, workers were bringing down a wall. Toulouse University was remodeling its Animal Behavior Department, turning it into a "laboratory of animal cognition." I took this as a sign of the times. Science is opening up to the intelligence of other species, and this is bringing down university walls, literally.

Giurfa turned to his computer and summoned up a full-screen image of the internal organization of the bee brain. He explained that a key part of their research involves looking into bee brains in search of the "neuronal substrate" of a given behavior. For scientists, the great advantage of the bee brain is that it can handle complex mental tasks with less than a million neurons. This simplifies research. Working with brain-imaging techniques, Giurfa and his colleagues mapped which parts of the bee brain are active when the animal learns about the smell of the outside world. Their research revealed the existence of a sensory-integration center called the "mushroom body," which is made of 170,000 densely packed neurons. This central component of the bee brain receives sensory input and directs behaviors"such as when bees dance symbolically to communicate information about the location of pollen-laden flowers, or navigate over long distances according to the sun"s position in the sky, or estimate the quality of potential nest sites.

Giurfa explained that they looked into the bee brain using a technique known as calcium imaging. Given that active neurons exchange calcium, one can open the skull of a living bee and bathe its brain in fluorescent substances that latch onto calcium and reveal the active parts of the brain. "This is another advantage of invertebrates," he said. "This process does not affect the animal. Invertebrates are enveloped in a capsule; their whole body is a capsule that is not innervated. It is very hard for us to imagine, but that is how it is. Imagine that instead of having skin, which is sensitive because it is innervated and filled with nerve endings, we had our internal system in armor."

"So the nerves stop with the brain?"

"Exactly. If you open it, if you make a small hole in a bee"s head, it is just like taking a helmet off. You do not hurt it because it is not innervated. The outside part of the insect which you can see is like a protection sh.e.l.l."

I viewed pain as an experience humans probably share with animals. I have pa.s.sed several gallstones, and know that pain has to do with the deep wiring of my body. I know just how paralyzing and excruciating it can be when raw nerves inside the body are sc.r.a.ped. Pain seems to be an undesirable experience one can have when one is equipped with a central nervous system. I knew nothing about pain among insects, but I figured that if their brains can handle abstraction, they can probably handle pain as well. I asked Giurfa if he thought bees feel pain. He said, "If you hurt a muscle, then, yes, you hurt the animal, but if you just remove a bit of sh.e.l.l, you do not hurt it. So you can delicately expose the brain, by fastening the bee in a tube, and you can look at what is going on."

Pointing at the map of the bee brain, he showed me the "olfactory pathway." On the tip of a bee"s antennas are olfactory receptors (corresponding to the mucus membrane inside the human nose), which feed chemo-electrical information into nerves leading to two small grapelike structures at the base of the brain (similar in shape to our own olfactory bulb). From there, wirelike neurons lead to the mushroom body, which processes the different inputs.

Giurfa and his colleague Randolf Menzel recently described the "cognitive architecture of the honeybee minibrain" as a network of independent units, the "modules of an insect mind." Each module treats information from a specific input, such as smell. The different inputs are then combined in a central locus, the mushroom body, where "context-dependent decisions" are reached. This enables honeybees to "extract the logical structure of the world."

Bees go out into the world equipped with a tiny brain and learn about their environment in next to no time. They have a lifespan of only two or three weeks. They seem ready to learn as soon as they hatch.

Some of Giurfa"s graduate students were running an experiment next door. He suggested we go and check their work. I followed him out of his office and found three students sitting at a white table gathered around an odd-looking device"a blue metal plate with a copper cartridge sticking out of one end. A bee was strapped into the cartridge. An array of small tubes was directed at its face. The graduate student conducting the experiment held a toothpick in his hand. He explained that when the antenna of a hungry bee is touched by a toothpick dipped in sugared solution, a reflex always occurs, causing the bee to stick out its tongue in a jerk reaction comparable to the reflex of a knee hit by a hammer. Giurfa explained that one could present an odor immediately before the sugar reward, and teach the bee to form an a.s.sociation that, in subsequent tests, causes the odor, rather than the sweetened toothpick, to release the tongue. This shows bees can learn about smell; it also reveals which parts of their brains are active when they do so. Bees, it turns out, can detect odors with greater sensitivity than dogs.

I looked closely at the bee in the cartridge. It was strapped in with blue tape. It could only move its antennas and tongue. Its head was glued to the back of the tube.

I chatted for a while with the graduate students. They were from Germany and said, speaking in English, that they loved Toulouse, which is near the Mediterranean, the Pyrenees, and the Atlantic, all at once. But they said it was more difficult to concentrate on science here; in Berlin, where it was "gray and rainy all year," they found it easier to work; here, they wanted to go on vacation all the time.

I focused once again on the bee. Spending an hour strapped in a bullet was a long time from a bee"s perspective. It did not seem very comfortable. I inquired about its fate after the experiment. Giurfa explained that the bees they tested in this fas.h.i.+on had to be killed, because otherwise they would return to the hive and falsify subsequent trials.

The bee I was observing had already experienced one nonrewarded odor and one rewarded one. Now it was about to receive the rewarded odor for the second time. We gathered around closely to see if it had learned something. The odor came out of the tube, and presto, the bee shot out its tongue. It had made the connection.

At that moment, I felt jubilation, and kins.h.i.+p with the bee. Like some humans, it was a fast learner. I asked Giurfa whether he thought finding intelligence in insects means they deserve better treatment. He said he agreed with the question and explained that there was research he would never do, in particular inserting electrodes into bee brains. He had not heard of animal-rights activists opposing research on invertebrates, though at the University in Berlin there had been much resistance to scientists studying vertebrate neurobiology. "At that time we chose the invertebrates exactly because we did not want to offend the sensibilities of some students," he said. "If you want to study biology of the whole, and see all the possible fields it has, you have to see and try these experimental techniques and approaches. Being an experimental biologist, I could never approve of thinking that everything could be done with simulations and models." He added that he would not perform the experiments he did on bees on cats, dogs, or apes, due to his "particular personal sensibility," which he knew was "just an anthropocentric point of view."

Though he refused to put electrodes into the brain of a living bee, he admitted that exposing the bees" brains and submitting them to calcium imaging was injurious to them, and would lead to their being killed. I returned to the question of whether bees feel pain. He laughed and called it a difficult question. In labs in South America, he said, scientists have shown that bee nervous systems produce opioids, presumably to induce a.n.a.lgesia. However, given that bees and humans are separated by hundreds of millions of years of evolution, he questioned whether the human concept of "pain" applies to bees. In his view, no one knows the answer.

I asked about the overall implications of his work on bee cognition. He said it shows that brain size is irrelevant when it comes to the capacity of performing highly demanding cognitive tasks. He also said it is time to do away with the arbitrary barrier that scientists have erected between vertebrate "learners," such as apes, pigeons, dogs, cats, dolphins, and humans, and all other "noncognitive organisms."

We spent half an hour with the students, then left them to their painstaking research and went out to lunch at a nearby restaurant. We talked about several subjects. He asked me about the Peruvian Amazon, where he had traveled. I asked him about his intellectual influences. He spoke of his thesis advisor in Argentina, and of his love for bees.

At one point I asked for his view on plant intelligence. He said the problem with plants is that they do not move, which makes it difficult to perform scientific experiments on them. I mentioned the parasitic dodder plant, which roams about and correctly gauges the nutritional content of other plants. He immediately suggested research questions about dodder. Can it learn to avoid certain substrates through negative reinforcements? If it demonstrates a capacity to learn, at what level of its cellular structure does the learning establish itself? "When you talk of learning, or cognition, the problem is that by definition you need a change of behavior resulting from individual experience," he said. "That is the only way to show that learning, or memory, has occurred. This means that all the approaches based on molecular biology"finding such-and-such a receptor or neuron X"are of no use whatsoever unless you demonstrate a change in behavior. When a given behavior changes, you can go and look into the box and find the molecules. But if you go looking for molecules without the change in behavior, you can say nothing. Learning manifests itself once the individual"s behavior changes. Changes at the cellular level are not necessarily relevant to this. And so, with plants, you need a visible change of behavior. That"s the challenge. But with the plant you mentioned, which moves, someone should be able to find something."

I asked him to comment further on how other scientists had received his research. He said that when he travels and presents his work, it is not questioned much. Rather, it leads other scientists to ask themselves questions they have not previously considered. He regards this as a success, even if his work does not provide answers to his main questions.

When asked if he could suggest any other scientists doing work on intelligence in nature, he mentioned an Austrian biologist studying cognition in amoebas. He also suggested several j.a.panese research teams: one working on color vision among insects, another on cricket olfaction, and a third on b.u.t.terfly neurology. "Go to j.a.pan," he said.

I left Martin Giurfa in front of his laboratory in the early afternoon. We promised to stay in touch. I felt elated, but also a bit dazed. I had come half expecting to meet a cold scientist. Instead I found a fellow who encouraged me to keep looking into intelligence in nature. I felt as if he had given me a license to continue deeper into unknown territory.

Chapter 6.

PREDATORS.

I returned to the Jura Mountains and spent the following months reading and thinking about plants and animals. Martin Giurfa had made me look into the relations.h.i.+p between movement and intelligence. It is true that some observers claim that plants lack intelligence because they do not see them move. But this is an optical illusion caused by the different timescales we operate on. Plants, in fact, do move.

Most plants move slowly, but some plants move fast even in human terms. A Venus flytrap can snap its leafy lobes shut in a third of a second to catch insects lured by its nectar. The flytrap is a predatory plant that eats flesh by secreting digestive juices and dissolving its prey. Its reflexes are triggered by electrical signals similar to those that run along our own nerves.

Unlike the Venus flytrap, most plants do not eat animals. Instead they take nutrition from sun and soil. Plants are also eaten in large amounts, being the basic element in all food chains. They are clearly successful at surviving, as they make up 99 percent of the ma.s.s of Earth"s living organisms.

Movement can be a criterion of intelligence among animals, but it does not apply to plants. They eat freely available sunlight and soil nutrients, so they mainly do not need to move from one place to another. Those among us who lack this ability are obliged to move about in search of food. Animals are, by definition, organisms that move to feed themselves. Animals are animate. They move.

Over the course of evolution, animals with efficient nervous systems have had an edge over their compet.i.tors. A nervous system that conducts information down to the muscles in a matter of milliseconds, rather than seconds, helps avoid being eaten. We use our brains to escape from predators. And as predators, we use them to catch our prey. This neurological arms race between animal predators and animal prey has certainly contributed to the development of brains such as our own.

But plants have not remained inactive. They may appear to sit around merely absorbing sunlight and being eaten in large amounts, but these brainless organisms have developed thousands of chemicals to try to stop themselves from being eaten. Plants have contributed to the arms race of evolution in the domain of chemistry. Unlike animals, they never had to develop movement or nervous systems to avoid predation.

We humans operate on a very rapid timescale compared to most plants. To us, plants can look stupid just sitting there. In fact, the term vegetable is an insult when applied to humans. According to the Concise Oxford Dictionary, it means "a person who is incapable of normal mental or physical activity, especially through brain damage; a person with a dull or inactive life." We have animal prejudices against vegetables, and they come out in our vocabularies.

I wanted to reconsider things from the start and try to move away from my own prejudices. As an animal, I wanted to understand animals. For starters, I learned that not all animals have brains. The sponge, for example, does not even have nerve cells. It lives attached to the sea bottom, or to other objects. The natural sponge that can be purchased in a store is the skeleton that supports the sponge animal. Inside this skeleton, the body of the living sponge consists of a kind of perforated stomach lined by whiplike cells which create currents that draw in water and food particles. A four-inch sponge can filter one hundred liters per day in this way. Sitting stuck to a rock at the bottom of the ocean, a sponge just sucks in its food. Zoologists recently discovered that one type of sponge can respond to potential danger by generating electrical impulses similar to those that streak through the nerves of other animals, including humans. Electrical signals disseminate through the sponge body via a network of fine strands of cytoplasm, which are not divided into cells. The sponge uses these signals to shut down the intake mechanism when the water around it becomes murky with particles that would otherwise clog its pores. These electrical signals are part of a decision-making system that allows the sponge to gauge and exploit the world around it. Though sponges are brainless and nerveless animals, they appear to make correct decisions on a regular basis.

The hydra is another brainless, headless, and sedentary animal that lives in water. It looks like a thin, translucent tube about an inch long and has a nervous system called a nerve net, which crisscrosses its body without forming a particular concentration. The hydra lives attached to vegetation by the base of its tubular body. The bottom of the tube is closed, and an opening at the upper end both engulfs food and rejects residue. Around this opening is a circlet of retractable tentacles that sting and catch other small invertebrate animals such as crustaceans. When a hydra detects a prey, it extends its tentacles and reaches out to grasp it. How it carries out this precise action with no brain is not known. Studies reveal that the animal"s nerve net concentrates around its mouth area. This suggests that the earliest heads appeared about 700 million years ago in hydralike organisms that may have been the common ancestors of species from snails to humans. The early head was simply a net of nerve cells at the mouth of the organism. This concentration of neurons close to the mouth shows how important active feeding is for animals. We exist in our current shape, with heads containing brains close to our mouths, as a legacy of this.

I scratched my head thinking about the fact that my brain is close to my mouth. I used my predator brain to think about the long line of predators that had led to me. I could see an endless queue of mouthed ancestors stretching back hundreds of millions of years, snapping their teeth and laughing.

I looked into the origin of central nervous systems. They first developed in small invertebrates like nematode worms. The present-day nematode Caernohabditis elegans looks like a mere speck to the naked eye. It has a body made up of fewer than one thousand cells, some three hundred of which are neurons that form a ring-shaped brain around the digestive tube not far from the mouth. The nematode brain, which is among the simplest known, is shaped like a saint"s halo. Centralized nervous systems have shorter and denser connections between neurons. This makes for quicker reactions to changes in the environment and for more complex behaviors.

The brown garden snail Helix aspersa has a central nervous system containing only a few thousand neurons. This is not much, considering it has a body the size of a walnut. Consequently, nervous signals take time to travel through the snail"s body, and its muscles can take several seconds to react to an outside stimulus. In fact snails perceive the world in slow motion. But this does not mean they make incorrect decisions. Snails are among the world"s most successful predators. There are about 65,000 species of snails, living in oceans, fresh water, and on land, in many different kinds of climates and environments. Snails are not stupid, but slow and efficient at what they do.

Octopuses have the largest brains among invertebrates, and scientists have noted their intelligence. Octopuses can run mazes, escape from locked tanks, break into other tanks and steal lobsters, open jars to get at crabs, disguise themselves, and even get angry and turn red. They have half a billion neurons" worth of brain power, which is about two hundred times less than ourselves, but a great deal more than snails. Octopuses are adept at finding food in concealed places"a skill usually a.s.sociated with big-brained vertebrates such as bears, pigs, and humans. Octopuses camouflage themselves by gauging their environment and, in a fraction of a second, transforming their body shape and the color, pattern, and texture of their skin. Octopuses are wily transformers.

Vertebrates include fish, amphibians, reptiles, birds, and mammals. We vertebrates have internal skeletons that allow us to achieve larger size than most other creatures. And we have backbones and skulls that partly enclose our central nervous systems, providing secure housing for eyes, ears, olfactory senses, and brains. This makes it easier to respond to the environment. But lacking a backbone does not make invertebrates stupid. Octopuses may be spineless, but they can run mazes as successfully as rats.

INTRIGUED BY THE CAPACITIES of invertebrates, I went to a zoology department at a Swiss university near where I live and asked if somebody could show me a nematode worm. I wanted to look at a living Caenorhabditis elegans through a microscope. The people at the zoology department were not used to dealing with such requests. After all, what business did an anthropologist have wanting to see a nematode? I explained I was writing a book about intelligence in nature and wished to see with my own eyes an invertebrate with a simple nervous system. My request was granted, and I was asked to wait.

On one of the walls in the corridor of the Zoology Department, there was a diagram of the complete body plan of a nematode. Each one of its 959 cells was mapped out in detail. A nematode is barely visible to the naked eye, but it is a complete animal, with skin, brain, mouth, digestive tract, reproductive tract including eggs and sperm, and a.n.u.s. Nematodes are among the animals that scientists have most studied. They are easy to keep in vast quant.i.ties and they reproduce very quickly. And they have transparent skin, which makes it possible to look into their living bodies with a microscope and see their organs function. They also have transparent eggsh.e.l.ls, so it is possible to watch their embryos develop.

Nematodes have brains that respond to taste, smell, temperature, and touch. And their neurons send one another an array of chemical signals including serotonin, which is a neurotransmitter that human brains also use. I may have several hundred million times more neurons than a nematode, but as a biological organism I share fundamental commonalities with it. Standing in the corridor looking at the worm"s body plan, I thought of myself as a kind of snaky organism with limbs. As a vertebrate, I differ from a worm in that I have a backbone and a brain encased in a skull. But like a nematode"and like most other animals"the bulk of my nerve cells is situated close to my mouth, and I have a long digestive tract. At the core of my being, there is a snakelike tube stretching from mouth to a.n.u.s.

Nematodes eat bacteria that they find in the soil. All animals feed on other organisms. Even vegetarians prey on plants. You cannot eat a carrot without killing it. Whether a vegetarian diet of plants is more ethical than an omnivorous one is a matter of opinion. I know I am a predator.

Putting an end to my reverie, a woman walked up to me and introduced herself as a geneticist working with nematodes. Her name was Monique Zetka. She came from the Czech Republic. We spoke in English. She was willing to interrupt her work to show me some nematodes.

I followed her into her office and asked about her work. She explained how she micro-injected DNA into nematode gonads in order to induce mutations in their eggs. She had several nematodes stuck on an oily slide and invited me to sit down at the microscope to take a look.

Once I got the swing of the apparatus, I focused on a single worm. The nematode was alive and moving. It looked like a transparent, Byzantine snake. Its internal organs had the intricacy of a racing-car engine, and it moved like a ballerina, ending each sideways weave with a flick at the tip of its body. I understood more clearly why the nematode"s scientific name includes the Latin word for elegant. I admired the nematode"s beauty for several minutes, feeling amazed that a creature with a brain of only three hundred neurons could move with such grace.

I found the experience thrilling. I turned to Monique Zetka and thanked her sincerely. As the quality of nematodes is not a frequently discussed subject, and as some people get uneasy taking such tiny creatures seriously, I asked with some hesitancy whether she liked nematodes.

She seemed embarra.s.sed by the question and simply said, "They are pretty nice." Scientists sometimes view their business as keeping a cold gaze in the face of nature"s elegance and beauty. I thanked her again and let her get on with her work.

I tried discussing my newfound enthusiasm for invertebrates with people around me, but often they just laughed. Many Westerners place themselves above "lowly" creatures such as nematodes. But humans are part of nature. Like so many other animals, we have eyes, noses, ears, mouths, teeth, brains, digestive tracts, skin, gonads, and so on. We are affiliated to even the simplest creatures.

The first animals were invertebrates. Animals with backbones and skulls only appeared about 500 million years ago. First came fish, then amphibians, reptiles, birds, and mammals. We humans are mammals. We belong to the order of primates, which includes marmosets, monkeys, apes, and chimpanzees.

Humans have several distinctive features, the most obvious of which is that we are the only living primates who walk full-time on two legs. According to the fossil record, some of the first bipedal primates belonged to a now-defunct genus called Australopithecus. These precursors of humanity lived about three and a half million years ago and had brains one-third the size of our own. Apart from their near-human posture, they were very much like chimpanzees, with similar diets and similar brain size. The first true hominids, commonly known as h.o.m.o habilis, appeared about two million years ago. They stood upright and had brains half the size of our own. Since then, hominid brains have continued to expand.

The fossil record is patchy and hard to interpret. Paleontologists do not agree on many details. When did the first h.o.m.o sapiens appear? Some believe that the roots of our species might extend back over four hundred thousand years. Others think that our immediate ancestors were a separate African species called h.o.m.o rhodesiensis, and that one should only apply the label h.o.m.o sapiens to fossils less than two hundred thousand years old. Some paleontologists believe that there have been different varieties of archaic h.o.m.o sapiens, including h.o.m.o rhodesiensis, h.o.m.o antecesor, and h.o.m.o heidelbergensis, from whom both modern humans and Neanderthals derived. Others view Neanderthals as an entirely separate offshoot of h.o.m.o rhodesiensis.

Our stocky Neanderthal cousins lived mainly in Europe and had a brain volume that was slightly superior to our own. Like us, they buried their dead, made musical instruments, and produced efficient hunting tools. Neanderthals were serious predators. a.n.a.lysis of their fossilized bones reveals that they had a heavy meat diet. Nevertheless, Neanderthals were also quite different from us. Their skulls were oval shaped, not round. Their foreheads were sunken rather than flat. Their chins were also sunken, whereas our own are pointed.

The fossil record suggests that anatomically modern humans, or h.o.m.o sapiens sapiens, emerged in Africa only about one hundred and fifty thousand years ago. This represents about seven thousand biological generations, and shows that we are a very young species. The word sapiens means "wise" in Latin. Whether this label truly corresponds to humans remains to be determined.

I found it fruitful thinking of humans as a species. It seemed clear that our great strength is being able to adapt to a wide variety of environments and circ.u.mstances. The descendants of the small band of humans that left Africa spread out across the world and populated it. From the Arctic to the deserts of Australia and the rain forests of the Amazon, they learned to exploit the plants and animals in each new environment they entered. Humans have long perpetrated ecological depredation. Species that were easy to hunt tended to disappear shortly after humans arrived in a given area. The fossil record indicates this clearly in places such Madagascar, New Zealand, and Australia. Like lions and wolves, humans are social predators. And we are an invasive species. Our outstanding capacity of adaptation makes us the most dangerous of all macroscopic predators currently stalking the earth.

Archaeologists have compared human campsites to those of Neanderthals living at the same time in the same region. Our ancestors made sophisticated traps and carved fine tools, not only out of stone and wood but also out of bone and antler. They carved bones into needles, which enabled them to sew clothes. Neanderthals probably lacked the capacity to make warm clothes. Our species cohabited the earth with Neanderthals for more than one hundred thousand years, and even traded with them in some cases. But there were four major glaciations during this period, and the Neanderthals did not survive. Paleontologists now think that their mysterious disappearance twenty thousand years ago is best explained by their incapacity to adapt to a changing environment.

h.o.m.o sapiens sapiens has a vertiginous trajectory. The Cro-Magnon artists who painted Lascaux, the prehistoric cave in southwest France, lived less than a thousand generations ago. They were humans just like us"but they had neither electricity nor sophisticated technology. Now humans have developed indoor plumbing, was.h.i.+ng machines, s.p.a.cecraft, computers, and an understanding of the intricate workings of biology.

Who are we? We have skulls and backbones, just like other vertebrate animals. Everything indicates that we are animals. Yet we do many things that animals cannot, such as write books, debate the meaning of words, turn trees into paper, study invertebrates with microscopes, equip jaguars with radio collars and track them, ride bicycles, fly planes, pilot submarines, travel to the moon and back, make wine from grapes, smoke tobacco, manipulate DNA molecules, build nuclear reactors, and study the extinction of other species. We can also step back from the world and witness it as a spectacle separate from ourselves, which we call "nature."

We are rooted in biology, and we can also think about it. Words and concepts are our specialty. We are the symbolic species par excellence. We can treat words as symbols for things that are not in our immediate vicinity. Our linguistic and symbolic capacities enable us to devise new relations.h.i.+ps between unrelated concepts. Through language, we can exchange information, make plans, scheme, and strategize. Mastering language and symbols has led us to the top of the food chain. Lions and wolves have fangs and claws; we have cunning concepts that we can put to practice.

Language also allows us to pa.s.s on vast amounts of knowledge and experience to our children. The sophisticated technologies we have developed in recent decades grew out of the acc.u.mulated knowledge of our ancestors. Language has blasted us onto a steep learning curve.

These developments have been made possible by our brains. We have big brains. Relative to body size, the human brain is three times larger than might be expected in a primate"and primates already have enlarged brains compared to other mammals. The top part of our brain, known as the cortex, has mushroomed during the evolution of hominids. Rita Carter describes this in her book Mapping the Mind: "One and a half million years ago the hominid brain underwent an explosive enlargement. So sudden was it that the bones of the skull were pushed outwards, creating the high, flat forehead and domed head that distinguish us from primates. The areas that expanded most are those concerned with thinking, planning, organizing and communicating. The development of language was almost certainly the springboard for the leap from hominid to human. It gave our ancestors lots to think about, and new brain tissue was needed. The frontal lobes of the brain duly expanded by some 40 per cent to create large areas of new gray matter: the neo-cortex. This spurt was most dramatic at the very front, in what are known as the pre-frontal lobes. These jut out from the front of the brain, and their development pushed the forehead and frontal dome of the head forward, reforming it to the shape of a modern skull."

Our brains are organized into distinct areas. First, at the top of the spinal column, at the base of the skull, there are cells sensitive to smell and light. This corresponds to the fish brain. On top of this lies a clump of cells called the cerebellum, which coordinates movement. Together the two layers form the reptilian brain. Further areas lie on top of this, including the thalamus (involved in the primary sensory processing of vision, sound, and touch), the amygdala (involved in emotion), the hippocampus (involved in learning and memory), and the hypothalamus (involved in motivation and behavioral regulation). This corresponds to the mammalian brain, which also has an additional top layer of cells known as the cortex. Some mammals have more cortex than others. In humans, the cortex balloons out of all proportions.

The architecture of the human brain incarnates our hereditary connection to other vertebrates, in their order of evolutionary appearance: first fish, then reptile, then mammal. But the human brain differs from other animal brains in that it is equipped with specialized neuronal circuitry to deal with language. For decades, scientists believed that two specific parts on the left side of the human cortex, known as Broca"s area and Wernicke"s area, function as "language centers." But recent research based on brain imaging shows that language is handled by many different brain regions working in parallel. As Susan Greenfield writes in her book Brain Story: "One of the most startling discoveries from such research is that saying just a single word causes a unique pattern of activity to ripple through the cortex. The experience of the word "screwdriver," for example, causes a part of the brain called the motor cortex to light up. The motor cortex is involved in controlling movement, so perhaps this word triggers memories of handling a screwdriver to become active. Obviously, language cannot be the preserve of just Broca"s and Wernicke"s areas"it involves an eruption of a.s.sociations and memories that are different for every word."

Humans have remarkably big brains compared to the rest of their bodies. Our children come into the world so top-heavy that they take months just to sit up. Their heads are so large that our species has by far the highest maternal death rate during birth. And young humans require long years of nurturance, education, and compa.s.sion for their brains to reach full potential. Humans also have by far the longest childhoods and adolescences, and human parents sustain compa.s.sion longer than parents from any other species.

Having a large number of neurons relative to body size certainly seems to enhance intelligence, as octopuses and humans demonstrate. But if intelligence is defined as the capacity to gauge the world and make correct decisions, there is some doubt that humans are as smart as some people fancy. Our current tendency to deplete the natural world with little consideration of the future shows that we do not yet have a grip on our predatory behavior. True, our species is very young. In comparison, octopuses have been around for several hundred million years, which has given them time to hone their skills. By comparison, we are just getting started.

Chapter 7.

PLANTS AS BRAINS.