One of my favorite locations in Japan is an uninhabited island just off the coast of the Izu Peninsula in Shizuoka Prefecture to the south of Tokyo. Uninhabited by humans, it is, however, inhabited by another primate: a troop of Japanese macaques.
Some friends and I have several times swum over to the island to explore it, though the first time we were almost repelled by stones rolling and bouncing down the sheer cliff face — stones launched by monkeys.
Among our group, the discovery earned the habitation the name Monkey Island, and ignited in me a continuing fascination with the animals. Sure, I knew they were nicknamed “snow monkeys” for their habit of taking outdoor winter baths in hot springs. They are the most northern-living of the world’s nonhuman primates, so it is perhaps not surprising that they have learned to make use of volcanically heated pools in Japan. And I also knew of the famous story of Japanese macaques washing sweet potatoes in the sea before eating them.
But witnessing them using a weapon (stones) against another species (me and my friends) was something else. It really brought home to me that the monkeys have a special kind of intelligence: An ability to understand the desires of others (we wanted to get onto the island).
I was thinking about Monkey Island at the Japanese Embassy in London earlier this year, where I attended an event to celebrate the 150th anniversary of the Anglo-Japanese Treaty of Amity and Commerce.
Signed in Edo (present-day Tokyo) in 1858, that treaty marked the start of a bilateral relationship between Japan and Great Britain that — notwithstanding the complicating fact that the countries were on different sides in World War II — has endured and strengthened to this day.
At the event I attended, scientists from both countries spoke about their work. By way of opening the proceedings, someone mentioned how the Japanese and the British have much in common — both being island countries located close to continental neighbors. We all clapped.
Then, with the pleasantries over, it was time for the scientists to take to the stage. The speaker who most enthralled me was Atsushi Iriki, who has a fantastic job title: Director of the Intellectual Brain Function Research Group, at RIKEN’s Brain Science Institute in Saitama Prefecture.
Iriki has uncovered some remarkable similarities — not between the Japanese and the British, but between two far more disparate creatures: humans and macaques.
Most of us know by now how smart the nonhuman apes are. Chimps, gorillas and orangutans have all been shown to have the intelligence necessary to use tools, solve problems, and even to think about another animal’s state of mind. What Iriki has done is to show that monkeys, too, have unexpectedly complex minds.
Iriki’s work suggests that Japanese macaques have a more interesting quality still than a fondness for rotenburo (open-air hot-spring baths): They seem to have a sense of self.
Self-awareness, long thought to be uniquely human, is a trait that has been granted to very few animals.
Regardless of the monkeys that rolled stones at us on Monkey Island, macaques are not thought to use tools naturally in the wild; apes, of course, do. But that doesn’t mean monkeys don’t have the capability to learn to use tools — and Iriki has taught his monkeys to do just that. With clever experiments, he has shown that when a monkey is holding a rake, say, in order to drag out-of-reach food to within grasping range, it incorporates the rake into its body image.
In other words, the monkey sees the tool in its hand as part of itself, just as we unconsciously think of a tennis racquet as we return a serve. The ability to do this, Iriki says, puts monkeys’ sense of body image equal to a 9-year-old human child’s.
Monkeys trained to use tools show growth and expansion of key areas of the brain. Their brains have the potential for huge increases in processing power. In short, Iriki sees the macaque as an important model of the evolution of our own brains.
A few million years ago, as our protohuman ancestors were evolving ever bigger brains, something similar may have happened to them. Perhaps it was the use of tools that was the trigger to the expansion of our brains.
Other work at Iriki’s lab in RIKEN shows that Japanese macaques have yet more abilities once thought to be the sole preserve of the great apes. Imitation, and pointing, for example.
If you point to something and a dog or a cat is watching you, they will (frustratingly) only look at the end of your finger, not at whatever it is you’re pointing at. If you do the same thing with an adult chimp (or a human child after the age of 2) it will look toward the thing you are pointing at. The chimp and the child understand that you want to direct their attention toward something.
Trained macaques in Iriki’s lab will follow the direction of a pointed finger, and will also imitate a human.
The Tosho-gu shrine in Nikko, Tochigi Prefecture has a famous carving over a doorway: three macaques, fashioned to represent the saying mizaru, kikazaru, iwazaru (“not see, not hear, not speak” — the Japanese equivalent of “see no evil, hear no evil, speak no evil”). Some claim that the Japanese macaque is the origin of the saying, though it is more likely that it was inspired by macaques of India or China hundreds of years before. Still, Iriki’s work is showing that there is even more to these other primates of Japan than meets the eye.
The second volume of Natural Selections columns translated into Japanese is published by Shinchosha at ¥1,500. The title is “Hito wa Ima mo Shinka Shiteru (The Evolving Human: How New Biology Explains Your Journey Through Life).”