Today we have similar problems; our current beliefs blind us, too. Evidence right before the eye can be distorted by the eye of the beholder quite as powerfully as it has been in previous ages of man. We can only hope that we have achieved greater insight and greater objectivity than some of our ancestors. The winds and currents of bias and prejudice blow hard and run deep in the minds of men. In one’s own mind these factors are difficult to see, and when seen, difficult to attenuate and to allow for their influence. If at times I scold my own species, do not take it too personally; I am scolding myself more than you.
You can see by now that I believe that some of the answers to the quest are in our own minds. We must develop, imaginatively and humbly, numbers of alternative hypotheses to expand the testable areas of the intellect and bring to the investigation new mental instruments to test and to collect facts germane to our questions.
To ask about the intelligence of another species, we somehow first ask: how large and well-developed is its brain? Somewhat blindly we link brain size (a biological fact) to intelligence (a behavioral and psychological concept). We know, in the case of our own species, that if the brain fails to develop, intelligence also fails to develop.
How do we judge in our own species that intelligence develops or fails to develop? We work with the child and carefully observe its performances of common tasks and carefully measure its acquisition of speech quantitatively. We measure (among other factors) size of word vocabulary, adequacy of pronunciation, lengths of phrases and sentences, appropriateness of use, levels of abstraction achieved, and the quality of the logical processes used. We also measure speed of grasping new games with novel sets of rules and strategy; games physical and/or games verbal and vocal.
Normal mental growth patterns of human children have been measured extensively in both performance and in vocal speech acquisition. I have taken the liberty of relating these to the normal growth of brain weight of children.
TABLE I
Threshold Quantities for Human Acquisition of Speech: Age and Brain Weight[7]
| Age (months) | Brain weight[8] (grams) | Speech stages[9] (first appearances) |
|---|---|---|
| 2 | 480 | Responds to human voice, cooing, and vocalizes pleasure. |
| 4 | 580 | Vocal play. Eagerness and displeasure expressed vocally. |
| 6 | 660 | Imitates sounds. |
| 9 | 770 | First word. |
| 11 | 850 | Imitates syllables and words. Second word. |
| 13 | 930 | Vocabulary expands rapidly. |
| 17 | 1,030 | Names objects and pictures. |
| 21 | 1,060 | Combines words in speech. |
| 23 | 1,070 | Uses pronouns, understands prepositions, uses phrases and sentences. |
[7]Lilly, John C. Man and Dolphin: A Developing Relationship. London: Victor Gollancz, 1962.
[8]Boston Children’s Hospital data from 1,198 records, in Coppoletta, J.M., and Wolbach, S.B., “Body Length and Organ Weights of Infants and Children,” American Journal of Pathology, IX (1933), 55-70.
[9]Summarized from McCarthy, Dorothea, “Language Development in Children,” in Carmichael, Leonard, ed., Manual of Child Psychology. New York: John Wiley, 1946, pp. 476-581.