【１】われわれが日常しばしば経験する事実として、次のようなものがある。われわれが本を貸した場合に、借りた人が用ずみの後直ちに自発的に返してこないことが少なくない。それは、どのような意識によって裏づけられているのであろうか。【２】その意識は、次の事実から推測され得るように思われる。すなわち、そのような場合に貸した人が本の返還を要求するしかたが、はなはだ特色的である。【３】私は何回か外人から本を借りたことがあるが、返還がおくれると、貸した人（外人）は、きわめて「事務的」に、「先日あなたに貸した何々の本は、もし用ずみなら返してもらいたい」と言ってくる。【４】われわれ日本人――少なくとも、私の知っている範囲の、私と同じくらいの年齢の人々――は、こういうふうに言うことに抵抗を感じ、若干悪びれて口実をもうけ言いわけをして（たとえば、「僕の友達であの本を見たいという者があるのだが。……」というふうに）でないと、返してもらいたいとは言えない。【５】あたかも貸主のこのような行動のしかたに対応するかのごとく、借主は、用ずみの後に直ちに返さないことについて何ら罪の意識をもたないのが普通であり、むしろ、返還の要求があるまで返さないでもっているのが当たりまえででもあるかのごとくであり、むしろ、返還の要求をうけても、悪びれることもなく、また言いわけをすることもないのが普通のようである。【６】私自身、本を貸してそのまま返してもらえないままになっている例は決して少なくない。極端な例としては、こんな経験がある。私は学生から或（あ）る本を貸してくれとたのまれ、快く貸したところ、二年ばかりたっても返してくれないので催促した。【７】彼はその本の各所にペンや鉛筆ですじをひいたままで、何の悪びれるところもなく返してきたのである。【８】……私の所有物である本を他人に貸したときは、私の現実支配の事実が終ったことによって、その本に対する私の所有権は弱いものになり、これに対応してその反面で、借主があらたにはじめた現実支配の事実は、私の所有権から独立した一種の正当性をもちはじめ、だんだん所有権に近いものになってくるように思われるのである。
　【９】このような例は無数につづくが、最近までも減ることなく新聞をにぎわしている問題としていわゆる役得という現象がある。役得というのは、或（あ）る地位についていることによって得られる利益で、∵しかも公式には承認されていないもの、を指すことばである。【０】役得には種々のものがあるが、ここでの問題に関係があるものとしては、他人の財産の管理にあたる者が、その管理財産で私的に飲食ないし宴会をしたり旅行に行ったりする場合をあげることができる。もちろん、その管理者がその地位にもとづく職務として他人を接待する必要があって、管理財産で飲食ないし宴会をしたり温泉に行ったりすることは、正当である。しかし、その範囲をこえて私的な目的でそのような行為をすることは、民事上は他人の財産に対する侵害であり、刑事上は「他人ノ為（）メ其事務ヲ処理スル者自己若クハ第三者ノ利益ヲ図り又ハ本人二損害ヲ加フル目的ヲ以テ其任務二背キタル行為ヲ為（）シ本人ニ財産上（）ノ損害ヲ加エタルトキ」（刑法二四七条）というのに該当して背任罪となるのである。会社の重役が会社の費用で、自分の私宅を建築或いは修理したり、私宅用の美術品を買入れたり……して、会社の財産状態を悪化させ、取引先ないし債権者ひいては経済界一般に大きな迷惑をかけた話が、最近の新聞の紙面をにぎわせたが、会社財産の実質上の所有者である株主に迷惑をかけたという最も重要なことが、新聞では必ずしも大きく取りあげられていないように思われる。（中略）いちばん面白いのは、第二次大戦中、「公物と思う心が既に敵」という標語が郵便局の壁にはってあった、という事実である。民法の所有権の考え方を前提するなら、「公物」――国民個人の所有物でなくて「公け」すなわち政府や府県市町村の所有物――と思うことは、それを国民個人の私的利益のために使ってはならない（他人の所有権を侵害してはならない）ということを意味するはずであるのに、この標語は逆に、公物と思うだけで「既に敵」だと言うのである。言うまでもなくその理由は、「公物」だと思うとむだに使う、という傾向があるからで、「むだ使いは敵だ」という戦争中の標語を特に「他人の所有物」たる公物について言ったまでのことである。
　（川島武宜（）「日本人の法意識」より）

Sigmund Freud tried to cure Viennese women of their neuroses, and Konrad Lorenz made his reputation studying birds, but the two men shared a belief that has become lodged in the popular consciousness. The belief is that we have within us, naturally and spontaneously, a reservoir of aggressive energy. This force, which builds up all by itself, must be periodically drained off -- say, by participating in competitive sports -- lest we explode into violence.
This is an appealing model because it is easy to visualize. It is also false. As an animal behaviorist has written: "All of our present data indicate that fighting behavior among higher mammals, including man, originates in external stimulation and that there is no evidence of spontaneous internal stimulation." Clearly, many people -- and, in fact, whole cultures -- manage quite well without behaving aggressively, and there is no evidence of the inexorable build-up of pressure that this "hydraulic" model would predict.
In 1986, a group of eminent behavioral scientists met in Seville, Spain, to discuss the roots of human aggression and concluded not only that the hydraulic model is inaccurate but, more generally, that there is no scientific basis for the belief that humans are naturally aggressive and warlike. That belief, however, has not been easily shaken. Among the arguments one sometimes hears are these: Animals are aggressive and we cannot escape the legacy of our evolutionary ancestors; human history is dominated by tales of war and cruelty; and certain areas of the brain and particular hormones are linked to aggression, proving a biological basis for such behavior.
The first thing to be said about animals is that we should be cautious in drawing lessons from them to explain our own behavior, given the mediating force of culture and our capacity for reflection. "Our kinship with other animals does not mean that if their behavior seems often to be under the influence of instincts, this must necessarily also be the case in humans," says an anthropologist. He quotes one authority who has written: "There is no more reason to believe that man fights wars because fish or beavers are territorial than to think that man can fly because bats have wings."
Animals are not even as aggressive as some people think -- unless the term "aggression" is stretched to include killing in order to eat. Organized group aggression is rare in other species, and the aggression that does exist is typically a function of the environment in which animals find themselves. Scientists have discovered that altering their environment, or the way they are reared, can have a profound impact on the level of aggression found in virtually all species. Furthermore, animals cooperate -- both within and among species -- far more than many of us assume on the basis of watching nature documentaries.
When we turn to human history, we find an alarming amount of aggressive behavior, but we do not find reason to believe the problem is innate. Here are some of the points made by critics of biological determinism:
Even if a behavior is universal, we cannot automatically conclude it is part of our biological nature. All known cultures may produce pottery, but that doesn't mean there is a gene for pottery making. Other institutions once thought to be natural are now very difficult to find. In a century or two, says a sociologist, "it is possible that people will look back and regard war in much the same way as today we look back at the practice of slavery."
Aggression, in any case, is nowhere near universal. The above-mentioned anthropologist has edited a book, which features accounts of peaceful cultures. It is true that these are hunter-gatherer societies, but the fact that any humans live without violence would seem to refute the charge that we are born aggressive. In fact, cultures that are "closer to nature" would be expected to be the most warlike if the proclivity for war were really part of that nature. Just the reverse seems to be true. Erich Fromm put it this way: "The most primitive men are the least warlike and ...warlikeness grows in proportion to civilization. If destructiveness were innate in man, the trend would have to be the opposite."
Just as impressive as peaceful cultures are those that have become peaceful. In a matter of a few centuries, Sweden has changed from a fiercely warlike society to one of the least violent among industrialized nations. This shift -- like the existence of war itself -- can more plausibly be explained in terms of social and political factors rather than by turning to biology.
While it is indisputable that wars have been fought frequently, the fact that they seem to dominate our history may say more about how history is presented than about what actually happened. "We write and teach our history in terms of violent events, marking time by wars," says a psychologist. "When we don't have wars, we call it the 'interwar years.' It's a matter of selective reporting."
The presence of some hormones or the stimulation of certain sections of the brain has been experimentally linked with aggression. But after describing these mechanisms in some detail, a physiological psychologist emphasizes that aggressive behavior is always linked to an external stimulus. "That is," he says, "even though the neural system specific to a particular kind of aggression is well-activated, the behavior does not occur unless an appropriate target is available...and even then it can be inhibited...."
So important is the role of the environment that talking of an "innate1'tendency to be aggressive makes little sense for animals, let alone for humans. It is as if we were to assert that because there can be no fires without oxygen, and because the Earth is blanketed by oxygen, it is in the nature of our planet for buildings to burn down.
All of this concerns the matter of human aggressiveness in general. The idea that war in particular is biologically determined is even more farfetched "When one country attacks another country, this doesn't happen because people in the country feel aggressive toward those in the other," explains a biologist. "If it were true, we wouldn't need propaganda or a draft: All those aggressive people would sign up right away. State 'aggression' is a matter of political policy, not a matter of feeling."
The point was put well by Jean Jacques Rousseau more than two centuries ago: "War is not a relation between man and man, but between State and State, and individuals are enemies accidentally." That states must "psych up" men to fight makes it even more difficult to argue for a connection between our natures and the fact of war. In the case of the nuclear arms race, this connection is still more tenuous. Says Bernard Lown, cochairman of International Physicians for the Prevention of Nuclear War, which received the Nobel Peace Prize in 1985: "The individual's behavior, whether he's aggressive or permissive or passive, is not the factor that makes up his outlook toward genocide. Even the person who's aggressive won't readily accept extinction."