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Brain Size
August 26, 2024
The
idea that
artificial Intelligence will eventually lead to
creation of a
superintelligence and an
existential threat to humans seems like a recent concern. However,
science fiction has often presented concepts like this
decades earlier, A superintelligent threat to humanity was introduced in July, 1958, in
Action Comics, no. 242, as the
cyborg,
Brainiac. Not unexpectedly, Brainiac's
Raison d'être is to collect all
knowledge in the
universe. Also acting as an
economist, he destroys the
primary sources of the knowledge he collects, reasoning that the knowledge is more
valuable if only he
possesses it.
Deep thought is what distinguishes
humans from other
animals. The brain is the
medium for thought; so, there's the idea that
brain size is important, with larger brains allowing more
profound thought. Larger brains in
hominids appears to have an
evolutionary advantage, as the following table illustrates.
There's a
current wave of
anti-intellectualism in the
United States, with people
deciding that
folk wisdom is a better guide in
decision-making than
discourse based on data and
scientific analysis. Recent examples include
climate change denial and the use of unproven
remedies for
diseases such as the
coronavirus.
Politicians have resorted to anti-intellectualism as a means to
rally the
common folk against their
elite oppressors. Anti-intellectualism was a part of
Richard Nixon's 1952
U.S. vice presidential campaign when he called the
opposition presidential candidate,
Adlai E. Stevenson II (1900-1965), who was running against
Dwight David Eisenhower (1890-1969), an "
egghead." Egghead is a
derogatory epithet for an
intellectual, and it was rarely used before the
20th century.[1]
Adlai E. Stevenson II (1900-1965) in 1961.
Stevenson ran against Dwight David Eisenhower (1890-1969) in the 1952 and 1956 US presidential elections, and lost both times. He was subsequently the United States Ambassador to the United Nations from 1961 until his death in 1965.
Stevenson was a grandson of Adlai E. Stevenson I (1835-1914), who was the the 23rd vice president of the United States under Grover Cleveland (1837-1908).
Wikimedia Commons image by Louis Fabian Bachrach, Jr. (1917–2010).
The largest animals do not have
proportionally larger brains, a trend that's not apparent for humans.[3]
Scientists have struggled for decades to understand the
relationship between brain and body mass in
mammals.[2] For the last
century,
conventional wisdom was that body mass in mammals could be described by a
power law; viz,
brain mass = (body mass) · xa
or it's
logarithmic representation,
log(brain mass) = a (log(body mass) + log x)
In which
x is an
intercept, and
a is called the
allometric coefficient, a coefficient supposed to reflect an underlying
scaling rule.[2]
Researchers at the
University of Reading (Reading, England) and
Durham University (Durham, England) created a large
dataset of brain and body sizes from about 1,500
species to determine the trend in brain size
evolution.[3] They confirmed that the largest animals do not have proportionally larger brains, finding that the trend is brain size and body mass is not
log-linear, but rather
log-curvilinear,
plateauing at high body mass.[2-3]
Chris Venditti, a
professor at the University of Reading and
lead author of the study, summarizes, "The relationship between brain and body size is a curve, essentially meaning very large animals have smaller brains than expected."[3]
Brain size and body size data for mammalian taxonomic groups showing the log-curvilinear relationship. (Fig. 1a of ref. 2,[2], released under a Creative Commons Attribution 4.0 International License. Click for larger image.)
As to the question of brain size evolution, the research team found that all groups of mammals demonstrated rapid
bursts of change, not only towards larger brain size, but smaller as well.[3]
Bats very rapidly reduced their brain size, suggesting that
flight may have imposed an
evolutionary constraint.[3] Homo sapiens has evolved more than twenty times faster than all other mammalian species, resulting in the massive brain size of modern man.[3]
Primates,
rodents, and
carnivores show a tendency for increase in relative brain size as they evolved.[3] As
Joanna Baker, a study co-author from the University of Reading, says,
"Our results reveal a mystery. In the largest animals, there is something preventing brains from getting too big. Whether this is because big brains beyond a certain size are simply too costly to maintain remains to be seen. But as we also observe similar curvature in birds, the pattern seems to be a general phenomenon – what causes this ‘curious ceiling’ applies to animals with very different biology."[3]
References:
- Egghead at the Google Books Ngram Viewer.
- Chris Venditti, Joanna Baker, and Robert A. Barton, "Co-evolutionary dynamics of mammalian brain and body size," Nature Ecology & Evolution (July 8, 2024), https://doi.org/10.1038/s41559-024-02451-3. This is an open access paper with a PDF file at same URL.
- Brain size riddle solved as humans exceed evolution trend, University of Reading Press Release, July 8, 2024.
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