The Evolution of Intelligence

Renato M.E. Sabbatini, PhD
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Studying the evolution of intelligence in the human line immediately recalls simular studies in our next-of-kin, our cousins, the apes. Without any doubt, they have some form of intelligence, and comparative studies have shed an important light on the understanding of our own intelligence.

There are only five living species of the great apes in the Pongid order, also known as anthropoids (meaning "similar to man"), of which three are represented below: the chimpanzee, the bonobo (very similar to the chimpanzees, but recently considered a new species), the gorilla, the gibbon (including the siamang) and the orangutan. With the exception of the orangutan, all other species are distributed in Africa's rain forest regions. The orangutan and gibbon lives in the rain forests of the islands of Java, Sumatra, etc.

As you can see here, their skulls and brains are anatomically very similar: large eye orbits in the same frontal plane, lateral and/or frontal bone ridges on the skull, large triangular nasal fossae, advanced upper mandibula, heavy maxila and strong teeth with large canines.
 

Chimpanzee (Pan troglodytes)

Gorilla (Gorilla gorilla)

Orangutan (Pongo pygmaeus)

The internal capacity of the skull is large and their brains are highly evolved and complex, second only to modern man's. Chimpanzees and gorillas have an average brain size of 400 and 500 cc, respectively. In consequence, apes are very intelligent and capable of symbolic manipulation similar to language, problem solving capabilities, highly complex behavior, learning, emotions, etc.
 

A young chimpanzee uses two stones to break up hard nuts

Dr. Savage-Rumbaugh teaching symbolic language to an ape using image blocks

For example, use of tools for many kinds of tasks have been well documented among apes, including the use of twigs, stones, branches, ropes, hooks, etc. However, they were never observed inventing or building tools (although at least one enterprising biologist has been able to teach a chimpanzee how to manufactures flint (stone) tools like a pre-historic human!). Of all the higher primates, only human beings and chimpanzees hunt and eat meat on a regular basis. Similarly, many research groups were able to demonstrate that apes are able to learn symbolic languages to communicate among themselves and with humans.

Apes are closely related to humans in terms of evolution. They were separated from us circa 36 million years ago, from a common ancestor, which has not been found yet. Thus, they can be considered a parallel branch of the evolutionary tree of humans. Extinct apes who are more ancient than the early hominids, such as Ramapithecus ardinus (5 to 6 million years old) are not considered hominids. Molecular biology studies have shown that Ramapithecus was more similar to orangutans.

The great apes' DNA sequences are 96,4% similar to those of humans. In other words, all our differences in brain, intelligence, dexterity, language, etc., are coded in only 3,6% of all genes that constitute our genomes.

The Author

"The Evolution of Intelligence" Renato M.E. Sabbatini, PhD Brain & Mind Magazine, February/April 2001

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