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Koko is a western lowland gorilla kept in San Francisco.

There are many claims about her IQ.

For example:

She was given IQ tests several times when she was younger and scored between 70 and 95, where 100 is considered normal for humans. Her carers insist she is not, however, a 'genius' gorilla, just typical for her species …

Is there any backing source for this? Which IQ tests (Raven's matrices? Wechsler's test? Or something else?) has she been tested with?

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Evidence:

  1. The tests given to Koko the gorilla were Cattell Infant Intelligence Scale, Peabody Picture Vocabulary Test, Ravens Progressive Matrices and Wechsler Preschool and Primary Scale of Intelligence. Chapter 14 of this document gives a description of those IQ tests. Research also showed that Koko was able to demonstrate some of the techniques required for abstract thought.

    It is hard to draw any firm conclusions about the gorilla’s intelligence as compared to that of the human child. Because infant intelligence tests have so much to do with motor control, results tend to get skewed. Gorillas and chimps seem to gain general control over their bodies earlier than humans, although ultimately children far outpace both in the fine coordination required in drawing or writing. In problems involving more abstract reasoning, Koko, when she is willing to play the game, is capable of solving relatively complex problems. If nothing else, the increase in Koko’s mental age shows that she is capable of understanding a number of the principles that are the foundation of what we call abstract thought. Source: Koko.org

  2. There have been other apes who have also performed well when intelligence tests were administered apart from Koko.

    Over the years other apes have been administered intelligence tests. An orang once reportedly scored about 200 on an infant intelligence test, a result that may have said more about the orang’s faster maturing motor control than its reasoning abilities, although there is no question that oranges are bright. Viki, the female chimp who was the subject of an early attempt to teach spoken language to an ape, was given a number of intelligence tests and performed quite well. She did better than a control group of human infants up to the age of eighteen months, and matched their performance until about age three. Source: Koko.org

    Some of the famous apes researched for language learning abilities are mentioned here.

  3. Research shows that there are differences in cognitive tasks when comparing between apes and young children.

    However, shared intentionality plays a role in all cultural learning, making this proposal modular and domain-general at the same time. It is consistent not only with increasing data on differences between apes and young children on cognitive tasks, but also with the idea that unique forms of human cooperation evolved along with and made possible human society and culture. Source: Modularity, comparative cognition and human uniqueness.

    There are also differences between human and animal brain structures.

    The broad range of cognitive cases, which includes teaching, causal reasoning, short-term memory, planning, TOM, etc., consistently shows fundamental limitations in the animal version of the human competence. There is no anomaly in the disparity—the disparity between human and animal cognition is compatible with the disparity between human and animal brain. Source:Human and animal cognition: Continuity and discontinuity

Meaning:

  1. The test scores of Koko's IQ is claimed to be 85 to 95 by Patterson.

    Koko's IQ has tested at 85-95 with several administrations of the Stanford-Binet Intelligence Scale and other such instruments as detailed by Patterson in her dissertation (1979b). This score range resulted in spite of the human cultural bias of the test. which placed Koko at a disadvantage. Source: Speech sound discrimination ability in a Lowland gorilla

    However, these IQ test scores should viewed with caution and should not be subjectively compared to a human child since it was obtained from a one subject longitudinal study and the high or low scores might depend on the primate's cooperation or mood which differs from one ape to another.

    With any single-subject study the limitations to making generalizations are obvious. How representative Koko's abilities are of gorillas' potential is anyone's guess at this point since hers is a one-of-a-kind longitudinal study. The literature (Redshaw, 1975; Yerkes & Yerkes, 1929), as well as observations (Patterson & Linden, 1981; personal observations), reflect how different one gorilla's performance can be from another's. Consequently, direct comparisons with child language development--even if theoretically other major variables, such as IQ and age equivalency, could be factored out--need to be made with caution. Source: Speech sound discrimination ability in a Lowland gorilla

  2. Critics of ape studies allege that the ape signs are only for obtaining food or objects and not for exchanging information with the ape's trainer.

    Nim's, Washoe's, Ally's, Booee's, and Koko's use of signs suggests a type of interaction between an ape and its trainer that has little to do with human language. In each instance the sole function of the ape's signing appears to be to request various rewards that can be obtained only by signing. Little, if any, evidence is available that an ape signs in order to exchange information with its trainer, as opposed to simply demanding some object or activity. Source: A Philosophical Critical Analysis of Recent Ape-Language Studies

TL;DR:

We have information only from observational studies about the intelligence of apes and more rigorous studies excluding Clever Hans effects or research bias are needed for confirming whether apes can obtain better IQ scores than human children or adults.

No matter how much we wish to project ourselves onto them, they are still apes—albeit very intelligent ones. They deserve our respect, and, at the very least, proper care. Our original plan for these apes—to study their capacity for language—has more or less been achieved, and it’s unclear how much more we can learn, as apes like Koko and Kanzi are reaching old age. Through these projects, we’ve learned about the ability of nonhuman apes to associate symbols or signs with objects in the world and to use this knowledge to communicate with humans. We’ve learned about the uniqueness of human language. But we may also have learned something about how strange, stubborn, and fanciful we can be. Source: Slate

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    Is there any research indicating that IQ tests on infants have any meaningfulness whatsoever? – user5341 Mar 12 '16 at 22:46
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    @user5341 that's a separate question. Also depends what you mean by "meaningfulness whatsoever". They obviously mean at least that the infant performed to a certain level on the test. – user30557 Mar 13 '16 at 6:48
  • Why do IQ tests specifically for children even exist? Isn't the entire (questionable) premise behind IQ tests, that they will try to give an objective assessment of a persons intelligence? Shouldn't kids be measured against the same scale that is used for adults? – fgysin Mar 15 '16 at 15:49
  • Its for maximizing learning opportunities for all children to study better-apa.org/research/action/intelligence-testing.aspx. – pericles316 Mar 15 '16 at 15:55
  • Nice answer. +1 TY – Citizen Mar 28 '16 at 21:53

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