"Why Are Some Animals So Smart?"


By Carel van Schaik C. ファン・シャイック
English 日本語 日本語
Even though we humans write the textbooks and may justifiably be suspected of bias, few doubt that we are the smartest creatures on the planet. Many animals have special cognitive abilities that allow them to excel in their particular habitats, but they do not often solve novel problems. Some of course do, and we call them intelligent, but none are as quick-witted as we are. 動物に関する本といっても,書くのは私たち人間なのだから,先入観のない客観的内容かどうか疑わしいものもあるだろう。だが,地球上で最も賢い生き物はヒトだということを疑う人はまずいないはずだ。特定の生息環境で特殊な認知能力を発揮している動物はたくさんいるが,彼らは未経験の問題を解決できないことが多い。一部にはその能力を備えたものもいて,私たちは彼らを賢い動物と呼ぶが,それでも私たちヒトのように頭の回転の速い生き物はいないだろう。
What favored the evolution of such distinctive brainpower in humans or, more precisely, in our hominid ancestors? One approach to answering this question is to examine the factors that might have shaped other creatures that show high intelligence and to see whether the same forces might have operated in our forebears. Several birds and nonhuman mammals, for instance, are much better problem solvers than others: elephants, dolphins, parrots, crows. But research into our close relatives, the great apes, is surely likely to be illuminating. なぜヒトという種はこのような際立った知能を持つ生き物に進化したのか。もっと厳密に言えば,何がヒト科の祖先にそうした進化を引き起こしたのか。それを知る1つの方法は,知能が高いとされる動物の進化の要因を探り,人類の祖先でも同じ要素が働いたかどうかを調べることだ。たとえば,ゾウやイルカ,オウム,カラスといった鳥類や哺乳類のいくつかの種は,ほかの生き物に比べて問題解決能力がかなり高い。しかし何と言っても,私たちヒトに極めて近い大型類人猿を調べるのが早道だ。
Scholars have proposed many explanations for the evolution of intelligence in primates, the lineage to which humans and apes belong (along with monkeys, lemurs and lorises). Over the past 13 years, though, my group's studies of orangutans have unexpectedly turned up a new explanation that we think goes quite far in answering the question. 霊長類──ヒトと類人猿が,サルやキツネザル,ロリスなどとともに含まれる系統──の知能の進化については,これまでさまざまな議論がなされてきた。ところが,今回,私たちのチームが13年間にわたって行ったオランウータンの調査から,こうした謎を解く新しい解釈が期せずして浮かび上がってきた。
Incomplete Theories
One influential attempt at explaining primate intelligence credits the complexity of social life with spurring the development of strong cognitive abilities. This Machiavellian intelligence hypothesis suggests that success in social life relies on cultivating the most profitable relationships and on rapidly reading the social situation--for instance, when deciding whether to come to the aid of an ally attacked by another animal. Hence, the demands of society foster intelligence because the most intelligent beings would be most successful at making self-protective choices and thus would survive to pass their genes to the next generation. Machiavellian traits may not be equally beneficial to other lineages, however, or even to all primates, and so this notion alone is unsatisfying.
One can easily envisage many other forces that would promote the evolution of intelligence, such as the need to work hard for one's food. In that situation, the ability to figure out how to skillfully extract hidden nourishment or the capacity to remember the perennially shifting locations of critical food items would be advantageous, and so such cleverness would be rewarded by passing more genes to the next generation. この仮説のほかにも,知能の進化を促す要因を考えることができる。たとえば,食物を得るためには知能が必要だといった説明だ。食物を探す場合,隠れた食べ物をいかにうまく取り出すことができるかという能力,そして季節を通じて変わっていく重要な食物が採れる場所を確実に覚えている能力も重要だ。そういう賢さは,より多くの遺伝子が次の世代に引き継がれていくということで見返りを得ることができるだろう。
My own explanation, which is not incompatible with these other forces, puts the emphasis on social learning. In humans, intelligence develops over time. A child learns primarily from the guidance of patient adults. Without strong social--that is, cultural--inputs, even a potential wunderkind will end up a bungling bumpkin as an adult. We now have evidence that this process of social learning also applies to great apes, and I will argue that, by and large, the animals that are intelligent are the ones that are cultural: they learn from one another innovative solutions to ecological or social problems. In short, I suggest that culture promotes intelligence. 私は知能の進化に最も重要なのは社会的学習だと考えている。このことは他のさまざまな要因とも矛盾するものではない。ヒトの場合,知能は時間とともに発達する。子どもはまず,辛抱強い大人の導きで学習する。社会的つまり文化的な強い入力がなければ,神童であっても,成長すると役立たずの大人になる。こういった社会的学習の過程が大型類人猿にもあてはまることが明らかになってきており,私は知的な動物は概して文化的な動物であると考えている。彼らは環境や社会について互いに学習しながら,革新的な解決法を見いだしているのだ。つまり文化が知能を高めるといえる。