5월 23일 추가지문과 일요일 추가지문

[하늘땅]

The evolution of intelligence among early

large mammals of the grasslands was due in

great measure to the interaction between two

ecologically synchronized groups of these ani-

mals, the hunting carnivores and the herbivores

that they hunted. The interaction resulting from

the differences between predator and prey led to

a general improvement in brain functions; how-

ever, certain components of intelligence were

improved far more than others.

The kind of intelligence favored by the inter-

play of increasingly smarter catchers and

increasingly keener escapers is defined by

attention-that aspect of mind carrying con-

sciousness forward from one moment to the

next. It ranges from a passive, free-floating

awareness to a highly focused, active fixation.

The range through these states is mediated by

the arousal system, a network of tracts converg-

ing from sensory systems to integrating centers

in the brain stem. From the more relaxed to the

more vigorous levels, sensitivity to novelty is

increased. The organism is more awake, more

vigilant; this increased vigilance results in the

apprehension of ever more subtle signals as the

organism becomes more sensitive to its sur-

roundings. The processes of arousal and concen-

tration give attention its direction. Arousal is at

first general, with a flooding of impulses in the

brain stem; then gradually the activation is

channeled. Thus begins concentration, the hold-

ing of consistent images. One meaning of intelli-

gence is the way in which these images and other

alertly searched information are used in the con-

text of previous experience. Consciousness links

past attention to the present and permits the

integration of details with perceived ends and

purposes.

The elements of intelligence and conscious-

ness come together marvelously to produce dif-

ferent styles in predator and prey. Herbivores

and carnivores develop different kinds of atten-

tion related to escaping or chasing. Although in

both kinds of animal, arousal stimulates the

production of adrenaline and norepinephrine by

the adrenal glands, the effect in herbivores is pri-

marily fear, whereas in carnivores the effect is

primarily aggression. For both, arousal attunes

the animal to what is ahead. Perhaps it does not

experience forethought as we know it, but the

animal does experience something like it. The

predator is searchingly aggressive, innerdirected,

tuned by the nervous system and the adrenal

hormones, but aware in a sense closer to human

consciousness than, say, a hungry lizard's instinc-

tive snap at a passing beetle. Using past events

as a framework, the large mammal predator is

working out a relationship between movement

and food, sensitive to possibilities in cold trails

and distant sounds-and yesterday's un forgotten

lessons. The herbivore prey is of a different

mind. Its mood of wariness rather than searching

and its attitude of general expectancy instead of

anticipating are silk-thin veils of tranquility over

an explosive endocrine system.