早稲田政経 2015 I

Humanity. Homo sapiens. Mortals. More than 150 years after Darwin published On the Origin of Species, society continues to turn to biology to separate man from beast because humans like to believe they are special. But just how special are we really?

When scientists first began to examine human DNA in fine detail, many thought it would finally close the question of what makes us human: our uniqueness would be written in the four-letter code that constitutes our DNA. At the time, no one knew how many genes humans had, with some scientists estimating the number to be upward of 150,000 genes, reasoning that such a complex species would need more genes than simpler organisms.

As the data was published, it quickly became clear that ( A ) truth. Humans have only around 20,000 genes that code for proteins; one tiny species of roundworm, C. elegans, has 18,500. Furthermore, our genes aren't significantly different from those of our closest animal relatives. Today, it is a pop-science truism that around 98 percent of human DNA is shared with chimpanzees.

So if DNA is less a plan for building a human and more a book for life shared by many species, where does it leave the human quest for uniqueness? Tim Lewens, of Cambridge University, says what is really different about humans is that we have a large body of inherited culture as well. "Humans are a species in which large amounts of inheritance are driven by culture," he says. "Much of what we pass on to our offspring is not genetic, but linguistic and cultural. We act in this way because we're an extraordinarily collaborative species. So it's not just that I tell my kids some useful things; it's that communities in the species as a whole construct legal institutions, libraries, schools, hospitals, and things like that." Humans create complex social institutions, in part, because of high intelligence, and this is one of the factors now considered important in explaining the difference between humans and other species.

But is human intelligence really unique? Scientists studying animal intelligence and behavior are increasingly making the boundaries between us and other species less ( B ), as Nicky Clayton, also at Cambridge, explains. "Many of the things that were thought to be uniquely human are, but in degree, not in kind," she says. "And because some of the most convincing evidence comes not from our closest relatives―the chimpanzees and bonobos―but from birds, this suggests these abilities have evolved independently and more than once." ( C ) "That's probably the most convincing evidence of a theory of mind in an animal because it shows the ability to project social experiences, to put oneself into another's shoes, so to speak."

So what things can humans do that animals definitely can't? "The obvious ways humans differ are in language and culture. No other animal reads and writes," Clayton says. "So I can show that the birds can remember what happened, where, and how long ago. But does that mean, in thinking about that event, the bird reminisces and re-experiences it? Well, of course, I've got no idea because, in the ( D ) of language, how would you do standard tests to ask them about their experiences?"

Although species like apes and gorillas produce rhythmic streams of sound that might be regarded as simple forms of language, only in humans is this used in a complex, abstract language system, says Usha Goswami, a professor of cognitive developmental neuroscience. Goswami studies how children learn language to understand what goes wrong in language development. "You don't find in any other species the ability humans have to combine linguistic elements, where you get a section of sound-like syllables ― for example, 'an-i-mal' or 'cat'―that shares no sensory features with animals or cats," she says. “You can also have reference for things that aren't in the here and now, and you can have abstract concepts like truth and beauty, the past and the future, and other possible worlds―something animals don't seem to have."

Goswami's research suggests some other reasons why human children are fundamentally different from animals. "My view would be that animals have a theory of mind that's limited to food," she says. "A baby will have a richer theory of mind because of all our communicative social tuning―there's a shared social element of human communication. For example, if it's learning through copying someone else's actions, and the person starts copying back, it will notice that." She adds, in concluding, that "animals can do bits of the things babies do, but no one species does enough of them to come anywhere close to the human being."

That, it would seem, is the heart of the matter. Our genetic basis is not unique. Nor is our collaborative culture. Not even language and intelligence are the privilege of the human species alone. But humans have developed and combined all these characteristics to an extraordinary degree, a degree far beyond that witnessed in any other species. And that is what sets human beings apart and makes them truly unique.

1. Use six of the seven words below to fill in blank space (A) in the best way. Indicate youx choices
for the second, fourth, and sixth positions.
(a) be (b) could (c) from (d) further　(e) less (f) nothing (g) the

2. Choose the most suitable answer from those below to complete the following sentence.
Scientific research has revealed that
(a) age is a principal factor in determining the structure of DNA.
(b) examination of an animal's environment helps us to understand genetic structure.
(c) human DNA is very different from the DNA of any other animal.-
(d) physical size and number of genes appear to be unrelated.
(e) scientists' predictions about the number of human genes were relatively accurate.

3. Choose the most suitable answer from those below to complete the following sentence.
The human species hands down a great deal of its culture to future generations
(a) as a result of having been on the planet for a long time.
(b) by producing as many offspring as possible.
(c) despite its inability to create diverse communities.
(d) in order to show that human beings are unique.
(e) through the establishment of social institutions.

4. Choose the most suitable answer from those below to fill in blank space (B).
(a) clear　　(b) intelligent　　(c) progressive　　(d) relative　　(e) vague

5. Choose the most suitable order of sentences from those below to fill in blank space (C).
(a) Back in 2001, Clayton and her team showed that jays, which typically hide food, would re-hide food if another jay had seen them hide it, something they never did when they had hidden food in private.
(b) "In other words, it takes a thief to know one," she says.
(c) One of Clayton's triumphs is demonstrating that a certain type of bird―the jay―has a theory of mind: it has the ability to understand the world from another jay's point of view.
(d) What is more, jays that re-hid food were birds that had themselves been thieves in the past.

6. Choose the most suitable answer from those below to fill in blank space (D).
(a) ability  (b) absence   (c) basis   (d) behavior    (e) experience

7 Choose the most suitable answer from those below to complete the following sentence.
According to Goswami, a human baby's theory of mind is
(a) concerned with food and not communication.
(b) focused on copying the actions of others.
(c) more complex than that of an animal as a result of communicative activity.
(d) not as well developed at the point of birth as that of a jay.

(e) the same, approximately, as that of apes that have been trained in the lab.


印刷用

解答は全訳の下

人類。ホモサピエンス。死すべき者。ダーウィンが『種の起源』を発表して１５０年たった今でも、社会は人と動物を分けるためには生物学に目を向ける。人類は特別なのだと信じたいからだ。だが、実際我々はどのくらい特別なのか。

科学者たちが初めてDNAを微に入り細に入り調べ始めた頃、多くの人は、私たちをヒトたらしめているのは何かという質問がついに閉じられるのではと考えた。つまり、我々の独自性はDNAを構成する４文字の暗号に記されているのだろう、ということだ。当時、ヒトがどれほどの数の遺伝子を持つか知るものは誰もおらず、150,000程度だろうと見積もる科学者たちが何名かいた。人類のように複雑な種は、より単純な有機体よりも多くの遺伝子を必要とするだろうという理屈だ。

データが発表されるにつれ、それが真実（A）ということがすぐに明らかになった。ヒトは、タンパク質生成の暗号となる遺伝子は20,000ほどしか持っていない。ちなみに、C elegansという微少なミミズ型生物は18,500だ。さらに、我々の遺伝子は、もっとも近い動物の種とそれほど異なっているわけではない。今では、ヒトの遺伝子の98%がチンパンジーと同じであるということはa pop-science truismである。

では、もしDNAがヒトを建築する計画ではなく、むしろ多くの種と共通する生命のための本だとすれば、そのことは、人類の独自性を求める探求を、どこにおくのであろうか（→意訳「～探求はどこに向かうのであろうか」）。Tim Lewnsは言う。ヒトが本当に他と異なる点は、相続される文化の総体を持つということだ。「ヒトという種においては、相続の大部分が文化によって推進されるのだ」と彼は言う。「我々が子孫に受け継ぐものの大部分は遺伝子ではなく、言語であり文化なのだ。我々がそのように行動するのは、異常なほど協調的な種であるからだ。つまり、私が自分の子供に役立つことを伝えるというだけではなく、ヒトという種全体のコミュニティーが、法体系や、図書館や、学校、病院のようなものを構築しているということだ」ヒトが複雑な社会体系を構築するのは、一部には、高い知能のおかげである。そしてこのことは、

しかし、ヒトの知能は本当に独特なのか。動物の知能や行動を研究している科学者たちは我々と他の種の境界線をますます（A）にしている。Nicky Claytonがこう説明する。「人類に独特なものだと思っていたものの多くは、程度において独特なのであり、種類が独特ということではないのです」と彼女は言う。「さらに、もっとも説得力のある証拠は最も近い親類、つまりチンパンジーやボノボでからではなく、鳥から出てきています。ですから、こういう能力は、別個に、そして一度でなく何度にもわたって進化してきたと考えられます」（C）「それがおそらくどうぶつの心についての理論の、もっとも説得力のある証拠です。社会体験を投影する、言ってみれば、自分を他人の立場に置くという能力を示しているからです」

では、ヒトができて、動物には決してできないことはどのようなことか。「人類が明らかに異なっている点は、言語と文化です。読み書きする動物は他にはいません」Claytonは言う。「つまり、私は、鳥が何がどれくらい前に起きたと記憶する能力があることを示すことはできます。しかし、そのことは、鳥がその出来事を考えているときに、reminisceして再体験しているということなのでしょうか。もちろん私にはわかりません。なぜなら、言語が(D)状態で、どうしたら、鳥に自身の体験について質問する学力テストをすることができますか」

猿やゴリラのような種はリズムのある音の流れ、つまり単純な言語とも考えられるものを作り出すことはできますが、ヒトにおいてのみ、それが複雑、抽象的な言語体系として使われいる、とGaswamiは言う。Goswamiは言語発達において子供が間違いを理解するために、どのように言語を使うかを研究している。「人間が言語的要素を結合するために持つ能力は、他のどの種にも見られません。（その能力というのは）「ど・う・ぶ・つ」や「ね・こ」といった音節のような音の単位を認知することです。その音節というのは実際の動物や猫とは感覚的な特徴を共有していはいません（→つまり「ね」という音が猫の実態とは関係がないということ。たとえば猫のことを「ミャー」と呼んでいればそれは少しは関係があるが）」と彼女は言う。「ヒトはまた、今ここにないものでも参照することができますし、真実、美、過去と未来などといった抽象概念を持つこともできます。動物はこのようなことはできないと思われます。

Goswamiの研究は、ヒトの子供が根本的の動物と異なる他の理由もいくつか示唆している。「私の見解は、動物は食物に関してのみ精神理論を持つということです」彼女は言う。「赤ちゃんはより豊かな精神構造を持っています。それは我々がコミュニケーションを通して社会に適合しているということから来ています。人間のコミュニケーションには社会的要素が共有されているのです。たとえば、赤ちゃんが誰かの行動をまねることで学習しているときに、まねられたヒトがまねを仕返すと、赤ちゃんがそれに気づくということです」と彼女は付け加えて結論づける「動物は赤ちゃんができることのごく１部をすることができますが、人間に近づくに十分なほどのことができる種は１つたりともありません」