Sizing Up Human Intelligence
By: Stephen Jay Gould
Exercises: J. Geffen
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1.
“Size,” Julian Huxley once remarked, “has a fascination of its own.” We stock
our zoos with elephants, hippopotamuses, giraffes, and gorillas. Jumbo was one of
P.T. Barnum’s greatest attractions until the beast’s fatal collision with a train engine.
This focus on the few creatures larger than ourselves had distorted our conception of
our own size.
2.
Most people think that Homo sapiens is a creature of only modest dimensions.
In fact, humans are among the largest animals on earth; more than 99 percent of
animal species are smaller than we are. Within our own order of approximately 190
species, only the gorilla regularly exceeds us in size.
3.
In our self-appointed role as “lord of all”, we have taken great interest in
cataloguing the features that permitted us to attain this lofty estate. The brain, upright
posture, development of speech, and group hunting (to name just a few) are often
cited, but I have been struck by how rarely our large absolute size has been
recognized as a controlling factor of our evolutionary progress.
4.
Despite its low reputation in certain circles, self-conscious intelligence is surely
the sine qua non of our current status. Could we have evolved it at much smaller body
sizes? One day, at the New York World’s Fair in 1964, I entered the Hall of Free
Enterprise to escape the rain. Inside, prominently displayed, was an ant colony
bearing the sign: “Twenty million years of evolutionary stagnation. Why? Because the
ant colony is a socialist, totalitarian system.” The statement scarcely requires serious
attention; nonetheless, I should point out that, first, ants are doing very well for
themselves, and secondly, it is their size rather than their social structure that prevents
the attainment of high mental capacity.
5.
In this age of the transistor, we can put radios in watchcases and bug telephones
with minute electronic packages. Such miniaturization could lead us to the false belief
that absolute size is irrelevant to the operation of complex machinery. But nature does
not miniaturize neurons (or other cells for that matter).
6.
The range of cell size among organisms is incomparably less than the range in
body size. Small animals simply have far fewer cells than large animals. The human
brain contains several billion neurons; an ant is constrained by its small size to have
many hundreds of times fewer neurons.
7.
There is, to be sure, no established relationship between brain size and
intelligence among human beings (the tale of Anatole France with a brain of about
1,000 cubic centimeters vs. Oliver Cromwell with well above 2,000 cubic centimeters
is often cited). But this observation cannot be extended to differences between species
and certainly not to ranges of sizes separating ants and humans. An efficient computer
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needs billions of circuits and an ant simply cannot supply them because the relative
constancy of cell size requires that small brains contain few neurons. Thus, our large
body size served as a prerequisite for our attainment of self-conscious intelligence.
8.
We can make a stronger argument and claim that humans have to be just about
the size they are in order to function as they do.
9.
Our skills and behavior are finely attuned to our size. We could not be twice as
tall as we are for the kinetic energy of a fall would then be 32 times as great, and our
sheer weight would be more than our legs could support. Human giants of eight to
nine feet have either died young or been crippled early by failure of joints and bones.
10. At half our size, we could not wield a club with sufficient force to hunt large
animals; we could not impart sufficient momentum to spears and arrows; we could not
cut or split wood with primitive tools or mine minerals with picks and chisels.
11. Since these all were essential activities in our historical development, we must
conclude that the path of our evolution could only have been followed by a creature
very close to our size. I do not argue that we inhabit the best of all possible worlds,
only that our size has limited our activities and, to a great extent, shaped our
evolution.
12. A human brain weighs about 1,300 grams (45.5 ounces) on the average; to
accommodate such a large brain, we have bulbous, balloon-shaped heads unlike those
of any other large mammal. Can we measure superiority by the size of our brains?
13. In absolute brain size, humans are surpassed by whales and elephants. But this
fact does not confer superior mental ability upon the largest mammals. Larger bodies
need larger brains to coordinate their actions.
14. We must find a way to remove the confusing influence of body size from our
calculation. The computing of a simple ratio between brain weight and body weight
does not work. A large number of very small mammals have higher ratios than
humans; that is, they have more brain per unit of body weight. This results from the
correlation between brain size and body size. Brain size does increase with body size,
but it increases at a much slower rate than body size.
15. If we plot brain weight against body weight for all species of adult mammals,
we note that the brain increases at about two-thirds the rate of the body. Since the
surface area of animals also increases about two-thirds as fast as weight, we
conjecture that brain weight is not regulated by body weight, but primarily by the
body surfaces that serve as end points for so many innervations. This means that
because their bodies are bigger, large animals have absolutely larger brains than
humans and that small animals have relatively larger brains than humans because
body size decreases more slowly than brain size.
16. For mammals, if we plot brain size vs. body weight on a graph, we solve our
paradox. The criterion that shows our superiority is neither absolute nor relative brain
size – it is the difference between actual brain size and expected brain size at that
body weight. To judge the size of our brain, we must compare it with the expected
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brain size for an average mammal of our body weight. On this criterion we are, as we
expected, the brainiest mammal by far. No other species lies as far above the expected
brain size for average mammals as does Homo sapiens.
17. This relation between weight and brain size gives us important insights into the
evolution of the human brain. Our African ancestor, Australopithecus africanus, had
an average adult cranial capacity of only 450 cubic centimeters. Gorillas often have
larger brains, and many authorities have used this fact to infer a distinctly prehuman
mentality for Australopithecus. A recent textbook states: “The original bipedal apeman of South Africa had a brain scarcely larger than that of other apes and
presumably possessed behavioral capacities to match.” But A. africanus weighed only
50-90 pounds (female and male respectively – as estimated by Yale anthropologist
David Pilbeam), while largely male gorillas may weigh more than 600 pounds. We
may safely state that Australopithecus had a much larger brain than other primates on
the correct criterion of comparison with expected values for actual body weights.
18. The human brain is now about three times larger than that of our
australopithecine ancestor. This increase has often been called the most rapid and
most important event in the history of evolution. But our bodies have also increased
greatly in size. Is this increase in brain size a simple consequence of bigger bodies or
does it mark new levels of intelligence?
19. To answer this question, I have plotted cranial capacity against inferred body
weight for fossil men who may represent our lineage: Australopithecus africanus:
Richard Leakely’s remarkable new find with a cranial capacity of 800 cubic
centimeters and an antiquity of more than two million years (weight estimated by
David Pilbeam from dimensions of the femur): the later African Homo habilis; Homo
erectus from Choukoutien (Peking Man); and modern Homo sapiens. The results
show that our brain has increased much more rapidly than the prediction based on
compensations for body size alone.
20. My conclusion is not unconventional, and it does reinforce an ego that we
would do well to deflate for the sake of other living creatures, and ourselves.
Nonetheless, our brain has undergone a true increase in size not related to the
demands of our larger body. We are, indeed, smarter than we were.
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Answer in your own words.
Answer the following question in English.
1.
To what factors – paragraphs 1-3 – is the prominence of the human race usually
attributed?
Answer: _________________________________________________________
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Choose the best answer.
2.
Most human beings – paragraphs 1-2 – tend to be unaware of the fact that
a. we are not lords of the universe.
b. the gorilla is in fact larger than we are.
c. we are not necessarily the tiniest creatures in the animal kingdom.
Answer the following question in English.
3.
What particular quality – paragraph 4 – was decisive in determining Man’s
status, and what was the precondition for its development?
Answer: _________________________________________________________
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Answer the following question in English.
4.
In what respect – paragraphs 5-6 – is Nature wholly unlike our modern
technological devices?
Answer: _________________________________________________________
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Answer the following question in Hebrew.
5.
What does the evidence provided by various animal species – paragraph 7 –
suggest about the connection between brain size and intelligence?
Answer: _________________________________________________________
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Answer the following question in English.
6.
To what – paragraph 7 – does the author attribute the ant’s rather limited
capacity?
Answer: _________________________________________________________
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Answer the following question in Hebrew.
7.
What thesis does the information provided in paragraphs 9-10 illustrate?
Answer: _________________________________________________________
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8.
List the animals that have larger brains – in absolute size terms – than human
beings:
Answer: _________________________________________________________
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Answer the following question in English.
9.
How would other mammals – paragraphs 15-16 – approximating the human
race in body weight compare with humans in terms of brain power?
Answer: _________________________________________________________
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Choose the best answer.
10. How does brain size – paragraphs 14-16 – relate to body size among animal
species?
Answer:
a. Body size may increase while brain size will remain static.
b. An increase in body size is accompanied by a corresponding, though not
proportionate, increase in brain size.
c. Any increase in body size will be followed by an absolute and relative
increase in brain size.
d. It is precisely the smallest animals that inevitably display the tiniest brains
in both relative and absolute terms.
Answer the following question in Hebrew.
11. On what basis does the writer – paragraph 20 – claim that we are indeed smarter
than we were?
Answer: _________________________________________________________
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Answer the following question in Hebrew.
12. Our African ancestor was inferior in brain size to many gorillas – paragraph 17;
however, his future dominance could already have been presaged even at that
stage. Why?
Answer: _________________________________________________________
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