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 animals, 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; however, certain components of intelligence were; improved far more than others.

The kind of intelligence favored by the interplay of increasingly smarter catchers and increasingly keener escapers is defined by attention—that aspect of mind carrying consciousness 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 converging 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 surroundings. The processes of arousal and concentration 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 holding of consistent images. One meaning of intelligence is the way in which these images and other alertly searched information are used in the context 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 consciousness come together marvelously to produce different styles in predator and prey. Herbivores and carnivores develop different kinds of attention 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 primarily 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, inner-directed, tuned by the nervous system and the adrenal hormones, but aware in a sense closer to human consciousness than, say, a hungry lizard's instinctive 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 unforgotten 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.

17. The author is primarily concerned with

(A) disproving the view that herbivores are less intelligent than carnivores
(B) describing a relationship between animals intelligence and their ecological roles
(C) establishing a direct link between early large mammals and their modern counterparts
(D) analyzing the ecological basis for the dominance of some carnivores over other carnivores
(E) demonstrating the importance of hormones in mental activity



18. The author refers to a hungry lizard primarily in order to

(A) demonstrate the similarity between the hunting methods of mammals and those of nonmammals
(B) broaden the application of his argument by including an insectivore as an example
(C) make a distinction between higher and lower levels of consciousness
(D) provide an additional illustration of the brutality characteristic of predators
(E) offer an objection to suggestions that all animals lack consciousness



19. It can be inferred from the passage that in animals less intelligent than the mammals discussed in the passage

(A) past experience is less helpful in ensuring the survival
(B) attention is more highly focused
(C) muscular coordination is less highly developed
(D) there is less need for competition among species
(E) environment is more important in establishing the proper ratio of prey to predator



20. The sensitivity described is most clearly an example of

(A) "free-floating awareness"
(B) "flooding of impulses in the brain stem"
(C) "the holding of consistent images"
(D) "integration of details with perceived ends and purposes"
(E) "silk-thin veils of tranquility"



21. The author's attitude toward the mammals discussed in the passage is best described as

(A) superior and condescending
(B) lighthearted and jocular
(C) apologetic and conciliatory
(D) wistful and tender
(E) respectful and admiring



22. The author provides information that would answer which of the following questions?

I. Why is an aroused herbivore usually fearful?
II. What are some of the degrees of attention in large mammals?
III. What occurs when the stimulus that causes arousal of a mammal is removed?

(A) I only
(B) III only
(C) I and II only
(D) II and III only
(E) I, II, and III



23. According to the passage, improvement in brain function among early large mammals resulted primarily from which of the following?

(A) The interplay of predator and prey
(B) Persistence of free-floating awareness in animals of the grasslands
(C) Gradual dominance of warm-blooded mammals over cold-blooded reptiles
(D) Interaction of early large mammals with less intelligent species
(E) Improvement of the capacity for memory among herbivores and carnivores



24. According to the passage, as the process of arousal in an organism continues, all of the following may occur EXCEPT

(A) the production of adrenaline
(B) the production of norepinephrine
(C) a heightening of sensitivity to stimuli
(D) an increase in selectivity with respect to stimuli
(E) an expansion of the range of states mediated by the brain stem