The physical similarities between humans and other mammals are quite plain. We are made of the same flesh and blood; we go through the same basic life stages. Yet reminders of our shared inheritance with other animals have become the subject of cultural taboos: sex, menstruation, pregnancy, birth, feeding, defecation, urination, bleeding, illness, and dying. Messy stuff. However, even if we try to throw a veil over it, the evidence for evolutionary continuity between human and animal bodies is overwhelming. After all, we can use mammalian organs and tissues, such as a pig's heart valve, to replace our own malfunctioning body parts. A vast industry conducts research on animals to test drugs and procedures intended for humans because human and animal bodies are so profoundly alike. The physical continuity of humans and animals is incontestable. But the mind is another matter.
Our mental capacities have allowed us to tame fire and invent the wheel. We survive by our wits. Our minds have spawned civilizations and technologies that have changed the face of the Earth, while even our closest living animal relatives sit unobtrusively in their remaining forests. There appears to be a tremendous gap between human and animal minds, yet the precise nature of this gap has been notoriously difficult to establish.
People tend to have opinions about animal minds that are in stark contrast to each other. At one extreme, we imbue our pets with all manner of mental characteristics, treating them as if they were little people in furry suits. At the other, we regard animals as mindless bio-machines -- consider the ways animals are sometimes treated in the food industry. Most people vacillate between these interpretations from one context to another.
Scientists too seem at times to defend contradicting views, apparently aimed at either securing human dominance or at debunking human arrogance. On the one hand scholars boldly assert that humans are unique because of things such as language, foresight, mind-reading, intelligence, culture, or morality. On the other hand, studies regularly claim to have demonstrated animal capacities that were previously believed to be uniquely human.
The truth, you may suspect, can often be found somewhere in the middle. In THE GAP I survey what we currently know and do not know about what makes human minds different from any others and how this difference arose. It is about time that serious headway is made on these fundamental questions. Nothing less than understanding our place in nature is at stake. There are also important practical implications of establishing the nature of the gap, for instance, in terms of identifying the genetic and neurological bases of higher mental capacities. Those traits that are unique to humans are likely dependent on attributes of our brain and genome that are distinct.
A clearer understanding of what we share with which other animals also can have profound consequences for animal welfare. Demonstrations of shared attributes of pain and mental distress in animals have changed many people's views on blood sports and cruelty towards animals. Establishing their mental capacities, their wants and needs, can provide a better scientific basis for our decisions about how different species should be treated. It may be time to challenge the notion that mentally sophisticated creatures are legally treated as objects, no different from cars or iPhones.
Comparative research has shown that our closest animal relatives, the great apes, share some extraordinary capacities with humans, such as the ability to recognize their reflections in mirrors. Such findings have led to calls to accept great apes into our community of equals, with legally enforceable rights. But we need to take into account not only their impressive capacities, but also their limits; because with rights come responsibilities -- such as respecting others' rights.
Though we may be perfectly happy to extend the right to life, liberty, and freedom from torture to apes (and so would be willing to prosecute someone who kills an ape), would we be equally happy with the other side of the coin? Would we be willing to put an ape on trial for murder? In 2002, Frodo, a 27-year-old chimpanzee studied by Jane Goodall, snatched and killed a fourteen-month-old human toddler, Miasa Sadiki, in Tanzania. I do not remember calls for a trial. Moreover, should we police ape-ape rights violations? Surely there would be little point in prosecuting male orangutans for rape or a chimpanzee for infanticide. Yet, people used to think animals could be held responsible like humans can. During the European Middle Ages, animals were in fact frequently put on trial for immoral acts such as murder or theft. They were given lawyers and penalties that matched those given to humans for similar crimes. For instance, in 1386 a court in Falaise, France, tried and convicted a sow for murdering an infant. The hangman subsequently hung the pig in the public square. Her piglets had also been charged but, upon deliberation, were acquitted because of their youth.
One of the key characteristics that makes us human appears to be that we can think about alternative futures and make deliberate choices accordingly. Creatures without such a capacity cannot be bound into a social contract and take moral responsibility. Once we become aware about what we cause, however, we may feel morally obliged to change our ways. So be aware, then, that all species of apes are under threat of extinction through human activity. We are the only species on this planet with the foresight capable of deliberately plotting a path toward a desirable long-term future. Plan it for the apes; because they can't.
Thomas Suddendorf, Ph.D., is a Professor of Psychology at the University of Queensland in Australia and a fellow of the Association for Psychological Science. He studies the development of mental capacities in young children and in nonhuman animals, and is particularly interested in fundamental questions about the nature and evolution of the human mind. He has received honors and distinctions from the Association for Psychological Science, the Academy of Social Sciences in Australia, and the American Psychological Association. He has written a dozen book chapters and published more than 60 articles, including a 2007 Behavioral and Brain Sciences paper with Michael Corballis on the evolution of foresight that has been singled out as one of the most highly cited in the field of neuroscience and behaviour. He has just completed his first trade book: "THE GAP -- The Science of What Separates Us From Other Animals"