Can a fly think? How about a dolphin? The mental lives of animals are turning out to be surprisingly complex
AT FIRST, the New Caledonian crow simply watches the menacing presence suspiciously, hopping around in circles to get the best possible view. Eventually, overcome by curiosity, it picks up a twig that it would normally use to forage for food and pokes the threatening object, before jumping back in apprehension. When the thing fails to respond – being a rubber spider – the crow gains confidence and returns to lift it this way and that, peeking at the underbelly.
The behaviour, recorded in a study led by Joanna Wimpenny, in Alex Kacelnik’s lab at the University of Oxford, certainly looks smart. You or I might well behave in a similar way were we to come across something strange and potentially dangerous. But what’s really going on behind those beady eyes? A deliberate thought process or mere animal instinct?
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The question of whether other animals can think has troubled some of the greatest minds throughout the ages. Aristotle and René Descartes believed that animal behaviour is governed purely by reflexes, while Charles Darwin and the 19th-century psychologist William James argued that animals might have complicated mental lives.
We are now closer than ever to settling this debate. Taking into account a wealth of reports of ingenious animal behaviours, including those of the New Caledonian crows, many biologists have come to believe that certain creatures really do have rudimentary thoughts. Meanwhile, the latest brain-imaging experiments are helping us understand what kind of anatomy might be necessary for a thinking brain. Although it’s unlikely that their mental lives are quite as complex as ours, there’s much more going on in their heads than you might think.
Despite its long history, the question of whether animals think used to be something of a taboo subject. Opinions began to change in the 1970s, when American zoologist Donald Griffin started to tackle the problem. He was one of the first people to discover echolocation in bats, and behaviours such as beavers’ ability to cut pieces of wood to precisely fit particular holes in their dams, and vervet monkeys’ capacity for using their calls to mislead others in the troop led him to suggest that animals could think.
Other zoologists, sceptical of what were mostly subjective and possibly anthropomorphised observations, were outraged. “Griffin came out with what I think was a crazy book, in which he said that all animals are conscious and every time any animal did anything with any ingenuity, as primitive as a firefly glowing in the dark, that proved it was conscious,” says Clive Wynne, who studies canine cognition and behaviour at the University of Florida, Gainesville. But Griffin’s work nevertheless invigorated the debate, Wynne says, and research is now more objective and systematic.
Very few today would agree with Griffin’s broad claims. More popular is the idea that the mental experiences of other animals lie on a kind of spectrum, ranging from a primitive kind of awareness to the rich and complex stream of thoughts in the human mind.
The fruit fly turns out to be the perfect animal in which to explore one end of this spectrum. Over the last few years, Bruno van Swinderen of the Queensland Brain Institute in St Lucia, Australia, has helped to show that these insects have an essential prerequisite for awareness: rather than responding randomly to everything around them, they can select what they pay attention to based on their memories. For example, the flies are more likely to explore new objects added to their environment than things that have been around for a while. And last year, van Swinderen’s team showed that reducing the fruit fly’s ability to form memories can damage their capacity to attend to novelty, so that the insects respond more randomly to their surroundings ().
Planning for the future
Flexible attention probably emerges even in the simplest brains, meaning many creatures, including fish, amphibians and reptiles, might also have this kind of awareness. Few would claim, though, that this rudimentary behaviour constitutes a thought process. So which animals, if any, show signs of the more advanced mental life that we humans experience?
The best clues so far come from animals that exhibit particularly complex forms of behaviour. An ability to plan for the future has been one important strand of evidence, for instance. Until recently, this trait was believed to be uniquely human, but in the late 1990s, Nicky Clayton at the University of Cambridge found that scrub jays can use specific memories of past events to forge plans for times ahead. In 2006, researchers at the University of Edinburgh, UK, found that this ability extended to hummingbirds. They can remember the location of certain flowers and how recently they had visited them and then use this information to guide future behaviour. Work published since then suggests that primates, rats and octopuses show some aptitude for forward planning.
The real test, however, is whether the behaviour is flexible. If not, the act might just be an evolved instinct, however complex it appears to be. The corvid family, which includes crows, ravens and jays, does seem to show this on-the-fly ingenuity. The Kacelnik lab’s New Caledonian crows, for instance, showed off their ability to use an old tool for a new job, when they probed the threatening rubber spider with their foraging twigs. The team published their work earlier this year (). Then there’s the case of Betty, a particularly intelligent crow who would bend a piece of wire on a twig in order to hook some food out of a test tube at the other side of the room. It is amazing that she could remember the food in the tube as she flew over to the branch, and then use the memory to solve a problem that wasn’t immediately in her field of view, says David Edelman of The Neurosciences Institute in San Diego, California. “That, to me, is strongly suggestive of a conscious process at work.”
Corvids might even be able to second-guess another bird’s behaviour. For example, experiments by Bernd Heinrich at the University of Vermont and Thomas Bugnyar at the University of Vienna, Austria, found that ravens will take steps to protect a secret food cache from other ravens that might have seen them hiding it, but were unconcerned about ravens stuck behind an obstacle that would have blocked their view (). “The work certainly suggests that these birds have the capacity to monitor both the experiences and perceived mental states of others,” says Edelman. In other words, they have a basic “theory of mind”, which should not be possible without some kind of thought process.
“Corvids might even be able to second-guess another bird’s behaviour and monitor its mental state”
Few other creatures are thought to have this ability, but not surprisingly primates are among this elite. If chimpanzees are stealing food, for example, they will be sure to be extra quiet if another member of the group is within earshot. More impressively still, they seem to be able to guess how another might have acted in the past. Earlier this year, Michael Tomasello at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, found that in a staged food hunt, chimps will try to guess where their competitors might have looked first, so that they can search the less obvious locations (). Whales, bears and dogs haven’t yet proved their abilities in this kind of task, but they nevertheless display some signs of empathy that suggest they too might have a relatively advanced mental life (see “You’ve got me feeling emotions”).
“If chimps are stealing food, they will be sure to be extra quiet if one of their group is within earshot”
Making a “pass”
Clever as these behaviours are, they may nevertheless lack one important characteristic of human thought, called “metacognition”. This is the ability to monitor and control memories and perceptions, allowing us to think that, “I know that I know this” or “I’m not sure that I’m right”, or to feel that someone’s name is on the tip of your tongue. According to David Smith of the State University of New York, Buffalo, its importance to human thought is comparable to that of language and tool use. Evidence for metacognition in other animals would therefore strike a blow for the existence of the animal mind.
Smith began exploring the subject with a flurry of papers in the early 2000s. For example, in one experiment, he presented a group of macaques with an image. After a short delay, the monkeys had to try and select the image from a group of four. The prize was a tasty peanut, but if they got it wrong, they won nothing. In one stream of experiments, however, the monkeys could forfeit the chance to win the peanut, in return for a guaranteed prize of a less desirable pellet of processed monkey food. Smith suspected that the monkeys would take this option to “pass” if they weren’t sure of the answer.
He was right. Monkeys given the chance to pass performed much better on the tests they did choose to take than those made to take the “all-or-nothing” experiments. This suggested that when given the opportunity, they were fully capable of assessing their confidence in the task, providing compelling evidence for monkey metacognition.
Further research suggests they are part of a select set with this ability (). Chimps, like macaques, have demonstrated metacognition time and again, but capuchin monkeys, although intelligent in other areas, seem to fall at this hurdle. The results for dolphins aren’t clear-cut, though it’s pretty certain that creatures like the humble pigeon just can’t step up to the challenge.
Finding out whether other intelligent species like dolphins, and perhaps crows, have metacognition is crucial to our understanding of the mind, says Smith. We need to know whether metacognition developed only once, in the line of Old World primates that leads to apes and humans. “Or did metacognition develop repeatedly and convergently, as the last frost that settles on all the highest peaks of cognitive sophistication in dolphins, crows, apes and people?” If that turned out to be the case, it would shake up our understanding of the evolution of the primate brain, he says.
With such a broad array of complex behaviours, many evolutionary biologists have conceded that at least some species have the rudiments of thought. Not everyone is convinced that we humans should step down from our pedestal just yet, however. Daniel Povinelli of the Cognitive Evolution Group at the University of Louisiana, Lafayette, for example, agrees that some animals are capable of thought, but he believes we are unique in our “higher” level of reasoning that allows us to grasp abstract ideas.
Chimps, for example, just don’t get abstract physical concepts, like weight, gravity and the transfer of force. Place a banana near a chimp’s cage and provide them with a few potential tools to reach their snack, and they’re just as likely to try something floppy as they are to reach for a rigid rod. He concludes that chimps can reason about things that are directly perceivable, but only humans have a higher level of thought that doesn’t solely rely on sensory input, allowing us to form more abstract concepts, like that of gravity or force. He also doubts that chimps have a theory of mind. “Message from Earth to comparative psychology,” he says, “humans are different.”
Wynne takes a more negative view but admits that he is in the minority. “The centre of gravity in the field is with people who would say that certain kinds of complex behaviour indicate consciousness in at least some animals,” he says. “But then there are the miserable sods like me, who don’t think that really any animals show consciousness, because we set the bar higher.”
Like Descartes, Wynne has come to the conclusion that language is essential for thought. “That’s because you can show me an ingenious behaviour – that does not involve language – and I conceive of doing it without being aware that I was doing it. The only behaviours that I cannot conceive of doing unconsciously are ones that involve using language.” Think of the complex actions that humans do all the time and that don’t require consciousness, he says. We can operate a complex piece of machinery – like a car, for example – without thinking about it.
The problem, says van Swinderen, is that behavioural studies can only go so far in addressing this problem. “You could show an animal like a fly doing something like putting on a hat and wearing clothes, and still some people would say it’s just a series of reflexes,” he says.
For this reason, some researchers are calling for new approaches that might settle the argument once and for all. Brain imaging provides some of the most promising possibilities. Aaron Schurger of Princeton University and colleagues, for example, have used functional MRI to study signatures of consciousness in the human brain. They have found that there is a similar pattern of neural activity each time we become conscious of the same picture of a house or a face, but not if we process information from the image unconsciously (). Such work suggests that conscious thought does not depend on any uniquely human region of the brain, meaning there’s no anatomical reason that it should be exclusive to people.
Other neuroscientific work has, however, revealed some important prerequisites for consciousness that might be present in some, but not all, animals. Neural connections that allow the thalamus to relay information from the senses to the cortex, for example, seem to be vital for conscious awareness. Other mammals also have such a pathway, so “at the very least they have the substrates in place for consciousness”, Edelman argues. “With recent advances in avian functional neuroanatomy, we can probably say the same about birds.” This would seem to fit with the conclusions of the behavioural studies.
If we’re on the hunt for evidence of conscious thought in other animals – whether vertebrates like reptiles and amphibians or invertebrates like the octopus and squid – it makes sense to look for analogues to the thalamus and cortex in those species as well, he says.
Even if these studies prove to be successful, some people will nevertheless take a lot of convincing. Wynne, for one, maintains that the debate is still best left for late night drinks, as he thinks no data will ever answer the question. But Edelman is optimistic that looking for animal equivalents of the thalamus and cortex will settle the arguments. “As far as I’m concerned, this could be the way out of centuries of debate.”
You’ve got me feeling emotions
While some researchers interested in probing animal minds are concentrating on tests of intellect, others are looking for evidence of an emotional life, which many think is an important constituent of consciousness.
Marc Bekoff, a biologist at the University of Colorado, Boulder, thinks there are clear signs that animals can experience empathy, spite, grief, gratitude, love and even awe. He cites, for example, a story of two orphaned grizzly bear cubs in Alaska. The male had been wounded, and limped and swam slowly, but his sister caught salmon for him to eat, and her support was crucial for his survival. Such evidence, he thinks, points to a sophisticated type of consciousness in a range of animals, including dogs, elephants and humpback whales.
