Why doesn’t brain size matter? Why is a rat with its tiny brain smarter than a cow? Why does the cow bother devoting all those resources to expensive gray matter? Eliezer posted this question in the February Open Topic, but no one took a shot at it.
FTA: “In the real world of computers, bigger tends to mean smarter. But this is not the case for animals: bigger brains are not generally smarter.”
This statement seems ripe for semantic disambiguation. Cows can “afford” a larger brain than rats can, and although “large cow brain < small rat brain”, it seems highly likely that “large cow brain > small cow brain”. The fact that a large cow brain is wildly inefficient compared to a more optimized smaller brain is irrelevant to natural selection, a process that “search[es] the immediate neighborhood of its present point in the solution space, over and over and over.” It’s not as if cow evolution is an intelligent being that can go take a peek at rat evolution and copy its processes.
Still, why don’t we see such apparent resource-wasting in other organs? My guess is that the brain is special, in that
1) As with other organs, it seems plausible that the easiest/fastest “immediate neighbor” adaptation to selective pressure on a large animal to acquire more intelligence is simply to grow a larger brain.
2) But in contrast with other organs, if a larger brain is very expensive (hard for the rat to fit into tight places, scampers slower, requires much more food), there are other ways to dramatically improve brain performance—albeit ones that natural selection may be slower to hit upon. Why slower? Presumably because they are more complex, less suited to an “immediate neighbor” search, more suited to an intelligent search or re-design. (The evolution process would be even slower in large animals with longer life cycles.)
I bolded “dramatically” because the possibility of substantial intelligence gains by code optimization alone (without adding parallel processors, for instance) also seems to be a key factor in the AI “FOOM” argument. Maybe that’s a clue.
Be careful about making assumptions about the intelligence of cows. I used to think sheep were stupid, then I read that sheep can tell humans apart by sight (which is more than I can do for them!), and I realized on reflection I never had any actual reason to believe sheep were stupid, it was just an idea I’d picked up and not had any reason to examine.
Also, be careful about extrapolating from the intelligence of domestic cows (which have lived for the last few thousand years with little evolutionary pressure to get the most out of their brain tissue) to the intelligence of their wild relatives.
I’m not sure if it’s useful to speak of a domesticated animal’s raw “intelligence” by citing how they interact with humans.
“Little evolutionary pressure” means “little NORMAL evolutionary pressure” for animals protected by humans. That is, surviving and propagating is less about withstanding normal natural situations, and more about successfully interacting with humans.
So, sheep/cows/dogs/etc. might have pools of genius in the area of “find a human that will feed you,” and may be really dumb in almost other areas.
At the risk of repeating the same mistake as my previous comment, I’ll do armchair genetics this time:
Perhaps genes controlling the size of various mammalian organs and body regions tend to grow or shrink uniformly, and only become disproportionate when there is a stronger evolutionary pressure. When there is a mutation leading to more growth, all the organs tend to grow more.
(I now see this answered in the first few comments on the link eliezer posted.)
Purely armchair neurology:
To answer the question of why cow brains would need to be bigger than rat brains, I asked what would go wrong if we put a rat brain into a cow. (Ignoring organ rejection and cheese crazed, wall-eating cows)
We would need to connect the rat brain to the cow body, but there would not be a 1 to 1 correspondence of connections. I suspect that a cow has many more nerve endings throughout it’s body. At least some of the brain/body correlation must be related to servicing the body nerves. (both sensory and motor)
The cow needs more receptors, and more activators. However, this would lead one to expect the relationship of brain size to body size to follow a power-law with an exponent of 2⁄3 (for receptors, which are primarily on the skin); or of 1 (for activators, which might be in number proportional to volume). The actual exponent is 3⁄4. Scientists are still arguing over why.
West and Brown has done some work on this which seemed pretty solid to me when I read it a few months ago. The basic idea is that biological systems are designed in a fractal way which messes up the dimensional analysis.
We have proposed a set of principles based on the observation that almost all life is sustained by hierarchical branching networks, which we assume have invariant terminal units, are space-filling and are optimised by the process of natural selection. We show how these general constraints explain quarter power scaling and lead to a quantitative, predictive theory that captures many of the essential features of diverse biological systems. Examples considered include animal circulatory systems, plant vascular systems, growth, mitochondrial densities, and the concept of a universal molecular clock. Temperature considerations, dimensionality and the role of invariants are discussed. Criticisms and controversies associated with this approach are also addressed.
Edit:
A recent Nature article showing that there is systematic deviations from the power law, somewhat explainable with a modified version of the model of West and Brown:
A recent Nature article showing that there is systematic deviations from the power law, somewhat explainable with a modified version of the model of West and Brown:
Why doesn’t brain size matter? Why is a rat with its tiny brain smarter than a cow? Why does the cow bother devoting all those resources to expensive gray matter? Eliezer posted this question in the February Open Topic, but no one took a shot at it.
FTA: “In the real world of computers, bigger tends to mean smarter. But this is not the case for animals: bigger brains are not generally smarter.”
This statement seems ripe for semantic disambiguation. Cows can “afford” a larger brain than rats can, and although “large cow brain < small rat brain”, it seems highly likely that “large cow brain > small cow brain”. The fact that a large cow brain is wildly inefficient compared to a more optimized smaller brain is irrelevant to natural selection, a process that “search[es] the immediate neighborhood of its present point in the solution space, over and over and over.” It’s not as if cow evolution is an intelligent being that can go take a peek at rat evolution and copy its processes.
Still, why don’t we see such apparent resource-wasting in other organs? My guess is that the brain is special, in that
1) As with other organs, it seems plausible that the easiest/fastest “immediate neighbor” adaptation to selective pressure on a large animal to acquire more intelligence is simply to grow a larger brain.
2) But in contrast with other organs, if a larger brain is very expensive (hard for the rat to fit into tight places, scampers slower, requires much more food), there are other ways to dramatically improve brain performance—albeit ones that natural selection may be slower to hit upon. Why slower? Presumably because they are more complex, less suited to an “immediate neighbor” search, more suited to an intelligent search or re-design. (The evolution process would be even slower in large animals with longer life cycles.)
I bolded “dramatically” because the possibility of substantial intelligence gains by code optimization alone (without adding parallel processors, for instance) also seems to be a key factor in the AI “FOOM” argument. Maybe that’s a clue.
Be careful about making assumptions about the intelligence of cows. I used to think sheep were stupid, then I read that sheep can tell humans apart by sight (which is more than I can do for them!), and I realized on reflection I never had any actual reason to believe sheep were stupid, it was just an idea I’d picked up and not had any reason to examine.
Also, be careful about extrapolating from the intelligence of domestic cows (which have lived for the last few thousand years with little evolutionary pressure to get the most out of their brain tissue) to the intelligence of their wild relatives.
I’m not sure if it’s useful to speak of a domesticated animal’s raw “intelligence” by citing how they interact with humans.
“Little evolutionary pressure” means “little NORMAL evolutionary pressure” for animals protected by humans. That is, surviving and propagating is less about withstanding normal natural situations, and more about successfully interacting with humans.
So, sheep/cows/dogs/etc. might have pools of genius in the area of “find a human that will feed you,” and may be really dumb in almost other areas.
.
At the risk of repeating the same mistake as my previous comment, I’ll do armchair genetics this time:
Perhaps genes controlling the size of various mammalian organs and body regions tend to grow or shrink uniformly, and only become disproportionate when there is a stronger evolutionary pressure. When there is a mutation leading to more growth, all the organs tend to grow more.
(I now see this answered in the first few comments on the link eliezer posted.)
Purely armchair neurology: To answer the question of why cow brains would need to be bigger than rat brains, I asked what would go wrong if we put a rat brain into a cow. (Ignoring organ rejection and cheese crazed, wall-eating cows)
We would need to connect the rat brain to the cow body, but there would not be a 1 to 1 correspondence of connections. I suspect that a cow has many more nerve endings throughout it’s body. At least some of the brain/body correlation must be related to servicing the body nerves. (both sensory and motor)
The cow needs more receptors, and more activators. However, this would lead one to expect the relationship of brain size to body size to follow a power-law with an exponent of 2⁄3 (for receptors, which are primarily on the skin); or of 1 (for activators, which might be in number proportional to volume). The actual exponent is 3⁄4. Scientists are still arguing over why.
West and Brown has done some work on this which seemed pretty solid to me when I read it a few months ago. The basic idea is that biological systems are designed in a fractal way which messes up the dimensional analysis.
From the abstract of http://jeb.biologists.org/cgi/content/abstract/208/9/1575:
A Science article of theirs containing similar ideas: http://www.sciencemag.org/cgi/content/abstract/sci;284/5420/1677
Edit: A recent Nature article showing that there is systematic deviations from the power law, somewhat explainable with a modified version of the model of West and Brown:
http://www.nature.com/nature/journal/v464/n7289/abs/nature08920.html
A recent Nature article showing that there is systematic deviations from the power law, somewhat explainable with a modified version of the model of West and Brown:
http://www.nature.com/nature/journal/v464/n7289/abs/nature08920.html
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Can something be mathematical and yet not strict?
Overly-simple mathematical models don’t always work in the real world.
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