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been secure enough in the uniqueness of our species to be willing to let it stand the test of scientific investigation. There has even been a certain nervousness about the tendency of those biologists with a strong concept of order to classify living things into species, genera, orders, families, and so on.
    By grouping animals according to greater and lesser resemblances, one develops a kind of tree of life with different species occupying different twigs of different branches. What starts out as an inescapable metaphor suggests only too clearly the possibility that the tree grew; that the branches developed.
    In short, the mere classification of species leads inexorably to thesuspicion that life evolved; that more intelligent species, for instance, developed from less intelligent ones; and that, in particular, human beings developed from primitive species that lacked the capacities we now consider peculiarly human.
    Indeed, when Charles Darwin published his
On the Origin of Species
in 1859, there was an outburst of anger against it, even though Darwin carefully avoided discussing human evolution. (It was to be another decade before he dared publish
The Descent of Man
.)
    To this day, many people find it difficult to accept the fact of evolution. They don’t, apparently, find the suggestion offensive that there are human characteristics in animals such as mice (who can be more lovable than Mickey?), but they do find it offensive that we ourselves may be descended from subhuman ancestors.
PRIMATES
    In the classification of animals there is an order called Primates, which includes those popularly known as monkeys and apes. In their appearance the primates resemble the human being more than any other animals do, and from that appearance it is natural to deduce that they are more closely related to human beings than other animals are. In fact, the human being must be included as a primate, if any sense at all is to be made of animal classification.
    Once evolution is accepted, one must come to the inevitable conclusion that the various primates,
including the human being
, have developed from some single ancestral stem and that all are to varying degrees cousins, so to speak.
    The resemblance of other primates to human beings is both endearing and repulsive. The monkey house is always the most popular exhibit in a zoo, and people will watch anthropoid apes (which most closely resemble the human being) with fascination.
    The English dramatist William Congreve wrote in 1695, however, “I could never look long upon a monkey, without very mortifying reflections.” It is not hard to guess that those “mortifying reflections” must have been to the effect that human beings might be described as large and somewhat more intelligent monkeys.
    Those who oppose the idea of evolution are often particularly hard on apes, exaggerating their nonhuman characteristics in order tomake less likely any notion of kinship between them and ourselves.
    Anatomical distinctions were sought, some little bodily structure that might be present in human beings alone and not in other animals, and most particularly not in apes. None has ever been found.
    In fact, the superficial resemblance between ourselves and other primates, and in particular between ourselves and the chimpanzee and gorilla, becomes all the deeper on closer examination. There is no internal structure present in the human being that is not also present in the chimpanzee and gorilla. All differences are in degree, never in kind.
    But if anatomy fails to establish an absolute gulf between human beings and the most closely related nonhuman animals, perhaps behavior can do so.
    For instance, a chimpanzee cannot talk. Efforts to teach young chimpanzees to talk, however patient, skillful, and prolonged those efforts may be, have always failed. And without speech, the chimpanzee remains nothing but an animal. (The phrase
dumb animal
does not refer to the lack of intelligence of the animal, but