June 4, 2009 | David F. Coppedge

“Social Brain Hypothesis” Discredited

According to evolutionary theory, the extra processing required for living in social groups should make brains bigger.  Not so, found a couple of scientists who looked into the question.  There’s no general correlation.
    According to Live Science, John Finarelli (University of Michigan) and John Flynn (American Museum of Natural History in New York) examined the largest number of species ever – 289 terrestrial carnivores, half of which were fossil species.  The “social brain hypothesis” (i.e., that brains of social animals tend to be bigger) may hold up for the dog family, but that’s about it.  It’s not true for weasels, bears and many other groups.  Some with large brains are non-social, and some social animals do not have proportionally larger brains.  Nature commented briefly on this find in today’s (June 4) issue, calling the old idea a “plausible hypothesis” that has now been “quashed.”  It continued, “The authors suggest that the ‘social brain hypothesis’ falls apart when looking at carnivore groups, extinct and otherwise, beyond modern canids (wolves, jackals, foxes and the like).”
    This undercuts what evolutionists thought they understood about brain size, or encephalization.  Flynn said, “Evolutionary change in encephalization is a widely observed phenomenon, but has been very hard to explain.”  Testing is good, he said, but this idea failed:

Increased brain size may mean different things to different groups, depending on unique evolutionary histories, ecologies, life history attributes etc.,” he said.  “That is to say, it might be that seeking simple, one-size-fits-all explanations across all mammals (or all amniotes [animals such as birds, mammals and reptiles that give birth to young inside eggs]) has been the problem all along.  Nevertheless, seeking general explanations (and then testing them with all available data), within clades or across groups, is a valuable goal of evolutionary studies.”

So explanation is a goal, not an accomplishment here.  Discounting a rule in this case, like saying brain size means different things to different groups, reduces the evolutionary explanation to the “Stuff Happens Law” – no explanation at all (09/15/2008).
    The falsification of the “social brain hypothesis” also undercuts the idea that intelligence is necessarily correlated with brain size increases.  Seth Shostak of the SETI Institute had just relied on brain size increase as a function of intelligence in an article about SETI for Caltech’s Engineering and Science magazine.1  In his always humorous way, Shostak employed encephalization as a principle that evolution tends to produce bigger brains, and thus increased intelligence, over time – because there’s a market for it:

Intelligence does appear to increase with time in some cases.  Above right is a plot by neuroscientist Lori Marino at Emory University that shows an index computed from the ratio of brain size to body size, the so-called encephalization quotient (EQ), for a bunch of species of dolphins and toothed whales over the last 50,000,000 years.  They were all pretty stupid 50,000,000 years ago, but 48,000,000 years later, white-flanked dolphins were the smartest things on the planet.  If you go to the local library and look up “Dolphin Literary Criticism,” it’s all from two million years ago.  Once you get to a certain level of complexity, there’s a niche market for intelligence, and it may get filled.

Flynn and Finarelli would argue that if Shostak had used more groups than just marine mammals, the correlation would have fallen apart.  Shostak’s article was accompanied by a picture of a dude with a photoshop-enlarged head being admired by a woman.  “This guy’s encephalization quotient is off the charts,” the caption reads.  “He’s going to be very popular as a potential mate.”  Maybe that works in captions, but not in the real world.  Real women would probably be grossed out, and his friends would call him a fat-head.  Besides, isn’t the trend in computers to put more processing power in less space?
    Speaking of mate choice, another evolutionary explanation has been discredited on that subject.  Science Daily said that “women may not be so picky after all about choosing a mate.”  A statement in the article makes it sound like evolution debunking has become commonplace: “That finding, of course, is contrary to well established evolutionary explanations about mate selection.”


1.  Seth Shostak, “When Will We Find the Extraterrestrials?”, Engineering and Science (PDF), Volume LXXII, Number 1, June 2009.

Another evolutionary myth has been falsified, and Seth Shostak has been embarrassed again.  Keep up the good work.

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Categories: Mammals, SETI

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