>Among terrestrial vertebrates, birds
and mammals generally exceed both amphibians and ‘‘reptiles’’ with respect to
cognitive abilities. Among birds, corvids and parrots stand out in this regard with
behavioral flexibility, innovation rate, tool use and tool fabrication, and also with
respect to truly mental abilities such as logical reasoning and mirror self-recognition––at
least in one corvid species.
Several groups of mammals, like dolphins and whales, dogs, elephants, and
bears (just to mention a few) show signs of high intelligence at least in some
cognitive domains. Primates on average exhibit an intelligence superior to all other
mammals. Among primates, there is a rather clear-cut ranking order in intelligence,
from the prosimians to monkeys and to the great apes. Except a few species
(e.g., capuchins), the great apes exhibit at least some aspects of cognitive and
mental abilities not found in monkeys regarding tool fabrication, insight into
causal mechanisms, mirror recognition, theory of mind, knowledge attribution,
metacognition, and consciousness.
However, humans, even under the most critical aspects, are superior to other
animals in all cognitive functions, no matter how astonishing the achievements of
the latter may be. The most clear-cut differences between humans and non-human
primates lies in two abilities that are interconnected: planning abilities and a
syntactic-grammatical language. When we compare the cognitive-mental abilities
of the most intelligent non-human animals with those of humans, then we find that
they roughly correspond to the abilities of children aged 2 1/2-5. As for linguistic
abilities, chimpanzees and gorillas equal a 3-year-old child, while with respect to
psychosocial abilities (empathy, theory of mind, etc.) they may be equivalent to
those of a 5-year-old child. In light of these empirical findings, the standard
question of whether human intelligence differs qualitatively or only quantitatively from the non-human one, may ironically be transformed into the question about
whether, with respect to cognitive functions, an adolescent or adult is qualitatively
or only quantitatively superior to a 3–5-year-old child. Besides maturation of
social competences, the most decisive feature that distinguishes humans from nonhuman
animals is the appearance of a syntactical-grammatical language at age 2 1/2, which is paralleled by an enormous increase in the capacity of working memory
and, consequently, intelligence, i.e., novel problem solving.
Therefore, the ‘‘rubicon’’ between animal and human intelligence seems to be
the evolution of the syntactical-grammatical language, which is essentially bound
to an increase in the ability to mentally manipulate processes (first actions, then
thoughts, then words) in the temporal domain. Once evolved, human language
served as a mighty ‘‘intelligence amplifier,’’ as was later development of writing
and invention of the computer.<
The long evolution of brains and minds
Gerhard Roth (2013)