Why are elephant and whale brains so large?

November 10, 2004 8:58 AM

Why are elephant and whale brains so large (much bigger than yours)? Their twice as big brains don't seem twice as smart as horses or dolphins, let alone humans. What is that extra gray matter doing? Pointers to scientific papers or experts appreciated.
posted by kk to science & nature (12 comments total)

Some of the expansion is probably due to a larger surface area, leading to a larger sensory cortex. (See homunculus.) They seem pretty darn accurate with that tail, and that would require fairly sensitive and specific neurons.
posted by gramcracker at 9:16 AM on November 10, 2004

Is isn't about the size of the brain somuch as it is about the ratio of the size of the brain to the size of the animal. Bigger animal, more musscles, longer spine, etc.

pwb.
posted by pwb503 at 9:29 AM on November 10, 2004

If a bigger brain for a bigger body was only about keeping the bigger body going, how did the huge dinosaurs get by with such small brains. They weren't that smart intellectually, but their huge bodies did not seem to need huge brains to operate. Why do whales and elephants?
posted by kk at 10:46 AM on November 10, 2004

>>how did the huge dinosaurs get by with such small brains.

They didn't.
posted by brownpau at 11:08 AM on November 10, 2004

They did for millions of years, brownpau.
posted by agregoli at 11:20 AM on November 10, 2004

Bigger bodies do not need (much) bigger brains, and the dinosaurs are a fine example of this. The real answer is that humans have gone through a lot of really weird evolutionary changes concerning the development of the configuration of our neural networks to include things like a 'Theory of Other Minds' module (used to model mental states of other humans for social interactions like lying), and an expansion on said module towards a more general purpose-effect (hypothetical universe/situational modelling for generic problem-solving).

I would guess the reason this happened to the primate line and not that of elephants or whales is because our very general-purpose bodies with extremely dextrous complex manipulators (hands) allowed for better use of tools and finer environment manipulation that the others. Improved problem-solving capability yielded significantly greater benefits.

Or it could just be the way the evolutionary cookie crumbled. *shrugs* It's a good question, though, and if anybody out there has a better answer at hand, I'd appreciate hearing it myself.
posted by Ryvar at 11:30 AM on November 10, 2004

Interesting fact I heard, but am not 100% sure of the truth behind it.

Human brains are, well, really really wrinkeled. These wrinkles (gyri) created an extremely convoluted surface topography -- and thus has an enormous amount of surface area. Since only the top few millimeters of the brain are actual "grey matter" (i.e. processing areas), humans probably have significantly more surface area/volume ratio, grey matter-wise.
posted by ruwan at 12:14 PM on November 10, 2004

You may be interested in these two articles on brain size, body size, and surface vs. volume of brain matter.
posted by jjg at 12:58 PM on November 10, 2004

A few months ago I read something (sorry, can't remember where) that "they" thought that intelligence depended on the size of the brain compared to the size of the spine (or possibly the spinal cord).
posted by deborah at 1:39 PM on November 10, 2004

Two points, from my general understanding:

1) For reasons explained above, the overall ratio of brain mass to body size isn't really a predictor of intelligence, since the characteristics that have to do with intelligence seem to be more related to the actual _structure_ of the brain than they do with the sheer mass of neurons. (cf ruwan's point on "wrinkliness", which I've also understood to be the case).

2) Also, as other people have pointed out, the bulk of the brain's mass is dedicated to sensory processing, rather than intellectual processing. As far as the "dinosaurs vs. elephants" issue, we don't know that dinosaurs didn't live in a sensorily very deprived world, compared to elephants and dinosaurs. Insects, worms, and many other creatures get along perfectly well today with almost no brain at all, proportionally speaking, because they work from very direct, straightforward representations of the physical workd around them.

It's very likely, on that front, that if you compared how an elephant perceived and processed its sensory input to a dinosaur, you'd find that the elephant had a much more detailed, precise sensory image of its world than a dinosaur did. (For example, do we have any idea whether dinosaurs saw in color? Even if they saw many more shades than we did, as bees apparently do, were they equipped to process many responses to those distinctions? Bees can see many more colors than we do, but they still have a drastically smaller set of possible responses to any stimulus.)

That doesn't mean that an elephant is necessarily any more or less _intelligent_ in how it responds to that input, but just that its sensory systems are much more evolved (which would make sense).
posted by LairBob at 3:51 PM on November 10, 2004

Elephants also have reasonably complex social lives, which might require more processing grunt.
posted by i_am_joe's_spleen at 9:21 PM on November 10, 2004

Thanks for the two paper links, jjg. That's the kind I was looking for.

For clarification, the elephant to dino comparison is one thing, but I am more interested in the elephant to horse comparison. Do we really think the elephant has a more sensuous experience than a horse? What is the elephant brain doing that the pretty smart (and social) horse brain is not?
posted by kk at 9:10 AM on November 11, 2004