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Biology 202, Spring 2005
First Web Papers
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Amanda Davis

As a Mawrtyr, I would like to think that I am relatively intelligent to the rest of the population. If I was not I would not be at Bryn Mawr. What does it mean to be intelligent? I thought of it in terms of number of neuropathways, how fast one processes information, and brain to body ratio. I think of human evolution and the proposed progression of our ancestors. I think of the invention of tools, fire, and most importantly symbolism as exhibits of our intelligence. I had thought of other animals, such as great apes and dolphins as being intelligent in similar ways that humans are. I had not, however, thought of different types of intelligence. The notion that intelligence evolves in different ways for each species in order to provide for that species (1). had not occurred to me. The neocortex, not necessarily the size of the brain is what is important in relation to intelligence (1). All mammals have a neocortex, but some mammalian species have more folding in their cortex than others (1). A human's neocortex is more important to functioning than that of a mouse (1).

How does one determine what aspect of the brain is responsible for intelligence? Brain mass does not seem to be responsible (2). For example, men have a higher average brain mass than women, but it has not been shown that men are overall more intelligent than women (2). Also, the person with the largest brain mass ever recorded (2850g) was also recorded to be an epileptic "idiot" (2). Larger animals tend to have larger brains than smaller animals, so brain mass in and of itself is not an "accurate comparative measure" (9). Body weight (S) to brain weight (E) ratios also do not appear to be responsible for intelligence (3). Mice and human E/S ratios are approximately equal, as are those of horses and elephants (3). It is clear that mice and humans are not equally intelligent, nor are horses and elephants. Additionally, an animal's body mass may fluctuate throughout its lifetime while brain mass in an adult animal remains much more constant (9). In order to correct the inconsistency of brain and body mass increasing proportionately, but not in relation to intelligence, an equation to find the encephalization quotient (EQ) is used (3). This is the ratio of a cephalization factor (C) which is a constant to the average mammalian value (3). Thus, an EQ of 3.0 would mean that the C constant is three times as high as would be expected in a mammal of that size and brain mass (3). Humans' EQ is higher than that of chimpanzees whose EQ is higher than a whale's (3). Common knowledge would verify that humans are more intelligent than chimpanzees that are more intelligent than whales. This however, does not imply causation, just a correlation.

The folding of the cortex may influence intelligence (4). The grooves are called sulci and bumps called gyri (4). Animals that are considered to be more evolved have more cerebral cortex and the "higher" animals within this group have more sulci and gyri in their cerebral cortex (4). The functions of the cerebral cortex include thought, memory, voluntary movement, language, reasoning, perception and information processing (5). The thickness of the cerebral cortex is fairly uniform in all mammals, so that aspect has no correlation to intelligence (5). Humans' brains with more folding correlates to our ability to reason and use language (5). Humans and primates do not, however have more neocortex than other mammals (6). Are different neurons then responsible for intelligence? There are twenty-seven times more other neural substances (i.e. glial cells, intracellular space) than neural cell bodies (7). All neurons are the same however. Neurons are the same in a starfish as in a frog as in a human. Neurons themselves may not be responsible for intelligence (7). What about brain structures? Are they different in animals of different intelligence? Higher primates and humans have a higher amount of neocortex than lower primates (8).

Measuring "brainpower" in relation to physical structures in the brain is crucial for understanding how intelligence is related to them (9). This proves to be much more difficult done than said (9). It is not known how to measure cognitive ability across species (9). There have been social implications in the evolution of primate intelligence (9). Since primates are social creatures, perhaps evolution has favored brain structures that support social behaviors (9). The temporal and prefrontal cortices have been implicated as these structures (9). There are many studies yet to be done to give us more insight into primate intelligence (9). "While ecology may have provided the initial conditions, cognitive evolution undoubtedly soon spiraled into a complex, interconnected web of adaptation, coevolution, and cooption of cerebral traits to cope with changing ecological and social conditions" (9).

It seems that there is still a significant amount of information about intelligence that is unknown. Before one can understand what makes one person more intelligent than another, it is crucial to understand what makes some species more intelligent than others. If the answer is in their brain structures, then possibly it is minor differences in these structures between human individuals that are responsible for differences in intelligence. As much diversity of intelligence exists among our own species, it is dwarfed by the diversity of intelligence in the animal kingdom.


1)What is Intelligence, Anyway??, Click on "Go here for a discussion" link.

2)The question of intelligence continues, on the Serendip website.

3)Thinking about brain size, on the Serendip website.

4)Cortical folding and intelligence, on the Serendip website.

5)More cortical folding and intelligence, on the Serendip website.

6) Neocortex, on the Serendip website.

7) Neurons and intelligence, on the Serendip website.

8) Brain structures and intelligence, on the Serendip website.

9) Evolution of Primate Evolution, by Scott Rifkin at Harvard.

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