Brain size needed for human-type cognition

I’m currently rereading Phillip Pullman’s His Dark Materials trilogy, and in The Amber Spyglass, there’s a species of humanoid beings that are about six or eight inches tall – small enough to ride a hawk, in any case. Since one of my cats was lying on my chest (with his head less than a foot from mine) as I was reading last night, I got to thinking about brain size.

Could a creature that small have a brain large enough to handle human speech, do tactical thinking, etc.?

In theory, yes. Brain size relative to body size is a factor in intelligence. Some birds show extraordinately high levels of reasoning with brains much smaller than a cow’s.

Isaac Asimov wrote a column on this issue - one of his monthly science columns. I’m afraid I can’t remember the name of it, but he got into the molecular mechanics of the brain and essentially concluded that mini-people aren’t possible, because the brain would not be big enough.

ETA: it may have been originally published in the late 60s, because what got him thinking on the issue was the TV show, Land of the Giants.

Well, to some extent it’s not the size, it’s how you use it. But even there, they still are talking about brains far larger than the brain of a creature 8 inches tall.

Meh, who needs lots of brain? Humans don’t.

Is Your Brain Really Necessary? (This is the first page of an article from Science, America’s most prestigious scientific journal. Unfortunately the rest of the article is paywalled. I have read it, though, and the message is that you can be a pretty smart cookie, and appear quite normal and intelligent, with very little brain tissue in your head.)

Also, more recently (a single page, open access article from The Lancet, Britain’s leading medical journal, about a Frenchman of very little brain, who is able to lead a normal life and hold down an office job):
http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(07)61127-1/fulltext

Any particular individual may be able to get by with little or no brain tissue, njtt, but I think the species as a whole would suffer if that became the norm. (Hm, wasn’t there a movie about that?)

There was a recent episode of NOVA that looked at the intelligence of birds. One variety of crow was able to use complex reasoning to employ a sequence of techniques using tools to recover a bit of food. The New Caledonian Crow is adapted to tool usage with a straight beak that allows manipulation of sticks and closer set eyes giving it the ability to focus on the tool held in it’s beak. The crow had experience performing each of the steps involved individually, but had never had to combine them in a specific sequence to obtain a reward. This showed a high level of tactical reasoning.

A small humanoid with a proportional head could contain a brain larger than the crow’s and would have even better tool using ability with his hands. Since he would have the physical characteristics necessary for spoken language it would seem possible that he could have the brain structure necessary to use those abilities. Possibly a larger portion of his brain could be dedicated to language and reasoning because of his smaller body not requiring as much of the brain for motor skills. He might actually be less adept at tool usage than the crow as a result of dedicating more of his brain for language and reasoning instead of manual dexterity.

The smallest living human, Jyoti Amge, is 23 inches tall and weighs 11 pounds. From the story, she appears to be of normal intelligence and other mental capabilities. Now, that’s a bit large to be riding around on a hawk (though it might be feasible for the largest eagles). I think eight inches would be pushing it, but perhaps not entirely out of the question if perhaps the brain was organized somewhat differently than a human’s.

But all the little green men I have seen pictures of had big heads for their size. What about that, huh? Bet them little suckers think pretty good because they have space travel & stuff.

Irene Pepperberg, a well known animal psychologist, claimed that her African Grey ParrotAlexhad an intelligence similar to that of Great Apes and dolphins, and even a five-year-old child. The claims of course have been controversial but have not really been refuted. In any case, Alex was exceptional even for an African Grey. An African Grey Parrot weighs about a pound.

One might also want to read up on Encephalization Quotient, a formula for estimating cognitive intelligence developed by psychologist Harry Jerison, that is based primarily on

Primates, cetaceans, and carnivores in general have EQ > 1.00 (with humans the highest); herbivores have lower EQ.

I do not understand what point you are making. The individual described at my second link is, apparently none too bright, and has some minor physical problems probably associated with his lack of brain tissue, but he is still well within the normal IQ range and able to have his own family and hold down a not entirely menial job. The person who is the main focus of my second link, however, had a high IQ, earned a good degree in mathematics, and (so far as one can tell from the the rather sketchy available information) apart from having a slightly larger than average head (filled mostly with fluid) was entirely normal in those areas where he was not above average. Why could not the human race get by if everyone were like that?

That was an excellent episode. The key take-away is that if you plot the brain size of mammals (and birds, I think) vs body weight, you get a pretty straight line. Notable exceptions (above the line) are humans (of course) and chimps. The Caledonian Crow scores an “above the line” number similar to chimps, although not as high as humans.

I’m thinking mostly about larger populations than two – yes, this pair does have an average IQ of 100, but it’s probably not a particularly representative population.

Mostly I’m thinking of how such beings would evolve – not an outlier who would be capable of using complex, non-instinctually based language after the rest of the species had developed it, but to be part of the population that came up with it in the first place. I realize that “only humans have language” is far from cut and dried, but it’s also a pretty reliable benchmark of “intelligence” whatever that means.

If the brains don’t have to be Earth-style brains then it might be possible to make them much smaller. For example, perhaps instead of using relatively bulky cells their brains are composed of molecular “circuitry” that’s laid down by cells (sort of like osteoblasts laying down bone). Or they still use cells, but theirs are smaller; bird cells are smaller than mammal ones so it’s possible for cell size to be smaller than ours.

It’s an open question really, because as far as I know nobody knows how such people do it. Most people with such a lack of brain tissue are severely mentally disabled. So it’s a question of whether or not whatever their brains are doing to function with so little tissue can be made to work across the entire population.

I am just not seeing why, if one human with only a small amount of brain tissue can have an IQ of 137, and be otherwise normal, it might not have been the case that humans, and human language and culture, evolved from the start with people having only around that amount of brain tissue.

Representativeness has nothing to do with it. These guys are living counterexamples, who refute the common assumption that in order to have human levels of intelligence a creature needs a brain pretty much as big (or as big relative to body size) as a normal human brain is.

I love it when nature “P’s” on the pillar of science.
I went to school with a guy that we were told had water on the brain. Long ago, prolly a fancy PC word used now. Other than a very noticeable large head he was otherwise as normal as the rest of the kids. Was actually one of the ‘smart’ kids but like to hang with some of us knuckle draggers… (Hydrocephalus) I got Google to work for me… Yea…

If brain capacity weren’t needed, brain capacity wouldn’t have been selected for. Extreme counterexamples after the fact don’t tell us anything.

This is spurious reasoning based on hyper-selectionism, which is generally recognized by biologists to be a false dogma. It is just not true that all features of organisms have been selected for. Some things just do not matter one way or another to survival or reproduction, and so do not get selected for or against (though they may change over time due to non-selectionist mechanism such as genetic drift).

Furthermore, even if brain volume is being selected for, the examples I gave strongly suggest that whatever advantage it confers has nothing to do with intelligence of cognitive function. (Perhaps big brains help regulate blood temperature better, or something.) That, in itself, is an important and surprising, conclusion.

These cases, as extreme as they may be, do help demonstrate that brain size is not the whole story about intelligence, which is the subject at hand. Given that 8" tall men are also extreme cases I think this information is germane even if it doesn’t offer a conclusive answer.