Descartes thought all animals were machines — simple reflex devices that couldn't even think because they did not have language. About 200 years later, Darwin expressed a totally different view of animal behavior—that animals can think, albeit without language. And in the last 50 years, a new area in psychology emerged called animal cognition. That's not an oxymoron because — going back to Descartes — animals do, in fact, use thought to represent objects and events in their environments.
Thus explained Dr. Herbert Terrace, Professor of Psychology and Psychiatry at Columbia University, in his introduction the thought-provoking event "Great Minds Think Alike — Or Do They?" at the German Center for Research & Innovation in New York City last month.
Dr. Terrace, the event moderator, also has done extensive research on ape language and primate cognition. He is the author of Nim, A Chimpanzee Who Learned Sign Language (Columbia University Press, 1979) and was featured in the documentary Project Nim, about an experiment that aimed to show that a chimpanzee might learn to communicate with language if raised like a human child.
If animals think, what does this imply about their brains?
If animals think, what does this imply about their brains? "If an octopus turns out to think in a similar way as we do, did the octopus develop a brain similar to humans? Or is the octopus able to come up with the same kind of thought but with a completely different brain?" asked the first speaker, Dr. Onur Güntürkün, Professor of Biological Psychology in the Department of Neuroscience at the Ruhr-Universität Bochum in Germany and winner of the 2013 Leibniz Prize, the highest German research award.
This question was at the heart of his provocative presentation, which took the audience from early, overarching theories of the evolution of the brain to recent, highly specific discoveries about commonalities and differences between the brains of birds and mammals.
'An unbelievable evolutionary success'
In the millions of years since the dinosaurs died off, "mammals captured each and every niche on this planet — and in every ecological system, we mammals are the top predators," Dr. Güntürkün said. "This is an unbelievable evolutionary success." Although there are many possible reasons for that success, "one is that we are very smart, and we outsmart all the rest of the animals."
Earlier theories of evolution — specifically that of the anatomist and neurologist Dr. Ludwig Edinger — held that the brains of different species evolved sequentially, with each class of vertebrate adding a new component and a new kind of thinking, Dr. Güntürkün explained. In other words, an amphibian reaches a higher level of cognitive competence than a fish, a reptile reaches a higher level of cognitive competence than an amphibian, and so on and so forth all the way up to humans. Thus, Dr. Edinger postulated, a reptile could never be taught something that is easily learned by a bird, for example, because the reptile is missing an area of the brain that a bird has, and a bird could never learn what can easily be taught to a dog or rat because only mammals have a neocortex.
Bird brains: more than meets the eye
Dr. Güntürkün was among those to prove Dr. Edinger's theory false. True, birds do not have a neocortex, nor is their brain laminated, like that of a mammal. Yet, from a functional standpoint, studies have shown that corvids, for example, reach similar levels of cognitive competence to chimpanzees with respect to imagination, causal reasoning, flexibility and prospection (the ability to look to the future). Similarly, magpies have been shown to recognize themselves in a mirror — a trait shared by humans and very few other mammals. Another study, in Science, showed that Caledonian crows were able to create a tool — a hook in an otherwise straight wire — to obtain food, and tool use is acknowledged to be a hallmark of advanced intelligence.
Taken together, the implications of these and other findings were irrefutable. In 2002, Dr. Güntürkün and other neuroscientists gathered at Duke University for the Avian Brain Nomenclature Forum. As reported in the Journal of Comparative Neurology, they decided that previous assumptions about avian brains were "in error." In certain respects, bird brains and mammalian brains are separate but equal.
"We concluded that birds have the same neurons that mammals have in the neocortex, but they're simply not arranged in lamina," said Dr. Güntürkün. "The internal architecture is vastly different, but the cells are homologous. The forebrain of birds and mammals is homolog, but mammals developed a cortical lamination, or perhaps reptiles inherited a lamination and just gave it up." Either way, it's clear that lamination is not a prerequisite for advanced cognition.
Other research revealed that the brains of birds, like those of mammals, are relatively large compared with the brains of reptiles, amphibians and fish. Yet, to solve complex cognitive problems, corvids use just 8.5 grams of brain, whereas chimps need 400 grams or more, according to Dr. Güntürkün.
Delving more deeply into molecular systems of both birds and primates, he and his colleagues discovered that "the biophysical properties at the heart of short-term memory in a primate brain also are at the heart of a bird brain," he said, even though the location in their respective brains is different. "This is a spectacular case of convergent evolution that goes down to the cellular architecture at the molecular level."
Delving more deeply still, Dr. Güntürkün and his colleagues looked at the connectome — a map of neural connections and neural interactions — of the bird brain. Analyses of the networks in the connectome can help identify similarities and differences between brains of different species, Dr. Güntürkün explained. They found that a bird's brain (in his study, a pigeon's) is what is termed a "small world" — a network of connections that combines high efficiency (short paths) with a high degree of clustering. It uses "hubs" — nodes that have more connections than other points and represent the shortest paths from one side of a network to the other.
"We found very similar hubs in the pigeon's brain as in a human brain," Dr. Güntürkün said. "Coming from a completely different route of evolution, the pigeon ended up with a brain that has the same molecular mechanisms, the same kind of internal connectivity and organization, and the same kind of thought as a mammal's brain, with high cognitive abilities, including self-recognition. Despite the absence of cortical layers, the avian brain conforms to the same organizational principles as the mammalian brain on a deeper, network-topological level."
Very recent work suggests that "birds may have miniaturized their brains to the extent that they have much smaller and much more densely packed neurons," he added. "But within these small brains they have spectacularly more neurons than you would predict from their brain volume." These findings have led Dr. Güntürkün to wonder why reptiles such as dinosaurs never developed big brains. "I think if you pack a brain with a completely different design, you cannot make it big. And our work over the next couple of years will focus on understanding why."
Primates and people: a common language?
Dr. William Hopkins, Professor of Neuroscience at the Neuroscience Institute and Language Research Center of Georgia State University, followed with perspectives on the evolution of communication and some of the brain changes involved in the development of language and speech, particularly among chimpanzees. He observed that at least 98% of a human's DNA protein will bind to a chimpanzee's DNA, making humans and chimps genetically closer than domesticated horses are to donkeys. Yet when it comes to language, important differences emerge.
If chimps have a "language-ready" brain, what are the components and behavioral outcomes of that brain? Dr. Hopkins and his colleagues are using an array of imaging techniques to find out. Their work has shown, for example, that chimps, like humans, have the equivalent of a Broca's area — an area of the brain involved with speech production — as well as a Wernicke's area, which is involved with speech comprehension. For chimps, the homologue of Broca's area is involved in gestures and facial expressions, rather than speech per se (chimp vocalizations are mediated by limbic areas). With respect to Wernicke's area, there is some evidence that chimps process species-specific calls in this part of the brain.
Despite the similarities, however, there are substantial differences in connectivity and activation in these and other areas of the brain that could explain, for example, how and why chimps use not speech, but rather a combination of gestures and vocalizations to communicate with each other and with humans.
Dr. Hopkins presented videos that showed the use of both strategies in different situations:
- Two chimps making up after a fight with a reconciliation gesture — namely, putting a finger in each other's mouth
- A chimp trying to convince a person to give her food by pointing to the food, clapping and alternating her gaze between the food and person
- Another chimp trying to get food by banging on her cage and making an attention-getting vocalization.
Dr. Hopkins provided other intriguing highlights of recent work, such as the discovery that chimps inherit particular vocalizations from their mothers that they can use as "alarm calls" in response to predators and possibly also to warn fellow chimps; that they gesture and communicate because they want something (usually food), never (as humans do) simply to share information; and that they'll use tools to obtain otherwise unobtainable foods by dipping a stick into a hole to get termites, for example. In captivity, if they want food that is outside a cage, they will use a human as a tool — behavior that is "at the interface of physical tool use and social tool use," he said.
Nevertheless, while acknowledging parallels between chimps and humans on functional and structural levels, Dr. Hopkins specifically "reinforced" Dr. Güntürkün's point about the importance of connectivity. He cited a recent study of white matter throughout the cortex of the human brain and the chimp brain, which found that chimps have proportionally more white matter in the primary motor cortex and primary somatosensory cortex, whereas the white matter in the human brain is concentrated in the prefrontal cortex — the areas of the brain involved in executive functions and inhibitory control.
"Although the idea of comparative anatomy is great, I believe that, ultimately, it's going to be connectivity — differences in the quantitative details of the system — that really informs us about how humans and chimps differ with respect to their language capabilities," he concluded.[divider]
Marilynn Larkin is an award-winning science writer and editor who develops content for medical, scientific and consumer audiences. She was a contributing editor to The Lancet and its affiliated medical journals for more than 10 years and a regular contributor to the New York Academy of Sciences' publications and Reuters Health's professional newsfeed. She also launched and served as editor for of Caring for the Ages, an official publication of the American Medical Directors Association. Larkin's articles also have appeared in Consumer Reports,Vogue, Woman's Day and many other consumer publications, and she is the author of five consumer health books.