I’ve heard it said that brain size is a rough indicator of intelligence potential. IIRC humans have the largest brains with dolphins our nearest competitors.
Now, I’m assuming this brain size/intelligence ratio is dependent on the ratio of brain size to total body size. I think an elephant’s brain is larger than a human’s when sat side-by-side but the elephant’s brain is smaller when compared to its total body mass (i.e. it’s a smaller percentage of the elephant’s total body weight).
When you hear that dinosaurs had a brain the size of a pea is that only true if you shrank a Brontosaurus to the size of a human or did they really have pea sized brains?
Dogs? I mean (jokes aside), a Chihuaha has roughly the same capacity for learning and intelligence as a German Shepherd even though the Shepherd’s brain is probably (WAG) 10x the size of the Chihuaha. Does this mean that nearly all of the brain is given to generating enough electricity to run the animal and the ‘smart’ parts are contained in a teeny portion that is the same across all dog sizes? If not that then what does a Shepherd do with the several billion neuron advantage it has over the Chihuaha? Put another way why aren’t Chihuahas and Poodles retarded compared to brainiac Shepherds and Great Danes?
This thread ultimately jibes with the brain usage thread running on how much brain power we really use. There is simply less ‘stuff’ in a small dog for cogitation but it certainly has no problem being as doglike as any other breed you care to name. Does this argue for lack of full brain usage? I.e. If we used all our brains then you would see a difference in intelligence among dogs.(I did read Cecil’s take on this BTW as regards whether we only use 10% of our brains.)
Carl Sagan discussed some of this in “Dragons of Eden” (I think that was the one). IIRC, there is a rough correlation of brain size to intelligence, but it’s not absolute. For one thing, it’s tough to measure & compare intelligence among different species. Also, the type of that brain mass is important…for example, amount of the cerebral cortex. Also also, there’s not even much of a correlation for brain size/intelligence among different people, never mind different species. (wasn’t there a recent thread about how Einstein’s brain was of a normal size?)
I hear what you’re saying Phobos and agree that the correlation between brain size and intelligence must needs be very loose. Also, there’s the problem of what ‘intelligence’ exactly is. You don’t see many ‘seeing-eye’ cats leading the blind yet dogs are comparitively easy to train for this task. However, if a cat asked a dog to climb a tree and catch a bird before it took off the dog would probably look pretty stupid in comparison as well. In short, a cat is smart at being a cat and posseses the skills necessary to its survival which are different from the skills a dog employs.
So, we can see that cross-species comparisons can be problematical but it still doesn’t answer my question on dogs. Human brain sizes may differ by a few percentage points even measuring extremes yet dogs can have brains coming in vastly different sizes. Here we have the same species with the same mental capacity (on average) across all members yet have brain sizes differeing from a few ounces to a few pounds. How is that reconciled?
Well, I’d contend with the claim that toy poodles, chihuahuas, etc. have fully-functioning brains… I think that they’re missing the part responsible for sanity. On the other hand, there are some small dogs, like beagles, say, or Jack Russels, that do seem relatively normal, mentally. My guess is that there’s more resources necessary to intelligence than brain size, so an animal will only be as smart as it needs to be. Heck, for all we know, a beagle could do integral calculus, if it wanted to… But that wouldn’t catch it any more birds, now would it? Why bother?
Another factor to consider when looking at “size” is the structure. I seem to recall that human brains are much more wrinkled than most animals. So even though an animal may have a larger brain based on weight, the human brain has a much greater surface area. I don’t remember why this is a factor in intelligence – perhaps it allows for a greater number of neural connections or flexibility.
Because the ratio of brain mass to body mass is generally steady across the various breeds. A chihuahua has a smaller brain than a boxer, but its brain is generally proportional in size to its body. If a four lb. chihuahua has a one ounce brain, I would expect a 60 lb. boxer to have a 15 ounce brain. (Numbers invented to make the point–I have no idea how large dog brains are.)
The other point to remember is that while the general ratios are determined to compare species, the variation within species can differ widely (and wildly). As a predictor of species intelligence, mean brain-mass/body-mass ratios provide a quick, general guide. Within any given species, all the individuals may vary so widely as to make the comparisons utterly worthless, as well as odious.
The encephalization quotient is the ratio of actual brain size to “expected” brain size, which depends on body size. Another measure of intelligence across species is the resting metabolic rate of brain tissue. See Intelligence, Brain, and Diet.
There is apparently only a weak correlation between EQ and intelligence. Some researchers attempt to find a correlation between cortical folding and intelligence, or between the number of neural connection per neuron and intelligence. See The question of non-human intelligence
I’ve never been up close and personal with any brains but rat brains (well, human brains, but everyone here is relatively familiar with the structure of the human brain);
the rat brain, I’ve noticed, is very good at doing what it’s supposed to. Rats sniff a whole TON, and not surprisingly, they have a MASSIVE olfactory bulb at the back of the brain. It can take up almost a quarter the mass of the brain (that’s an eyeball estimate), maybe more.
Another issue to consider is smooth-brained vs. wrinkle-brained. You take one animal with a 4-ounce brain and another with a wrinkly 4-ounce brain and you’ll probably note higher function in the wrinkled brained animal. The various fissures and sulci aid to increase surface area. Of course, the wrinkled 4-ounce brain will probably occupy a larger space, too.
Some animals (there’s a type of sea slug, Aplysia) have neurons that are larger (and I would assume, heavier) than others… the sea slug in question is very useful for studying the effect of electrical stimuli on neurons because the neurons are nice and large, so even a ham-fisted scatterbrain like me can land an electrode in it.
Anyhow, long story short, I don’t think mass is all where it’s at, but it does make some difference, of course.
Ok. I get that brain size vs. intelligence is, at best, a very weak guide to intellectual capacity. In the absence of any other evidence (i.e. all you have to go on are a few 10 million year-old fossils) this might serve as a vague indicator but no one would be willing to bet money on it.
I still have a problem with the dogs though. Take our Chihuahua and German Shepherd again. Let’s assume that the Shepherd has a brain 10x the size of the Chihuahua (no idea really…just illustrating my point).
Now, in all tests we care to throw at the two dogs they perform basically identically. Neither one is showing an intellectual superiority over the other.
After our tests we dissect the dogs (sorry PETA but this is important science) and look at their brains. The Chihuahua’s brain weighs 1 pound and the Shepherd’s brains weighs 10 pounds. Being very patient and using technology only I possess (but is thouroughly reliable and 100% accurate) we count every neuron in both brains. Turns out the Shepherd has exactly 10 billion neurons to the Chihuahua’s 1 billion neurons (convenient huh?).
Conclusions:
Brain vs. body size ratio is the same for both dogs.
Both animals test equally on all IQ tests.
The Chihuahua has 1/10th the number of neurons as the Shepherd.
Questions:
What are the other 9 billion neurons on the Shepherd doing since they are NOT related to intelligence?
Can one say that ‘intelligence’ (whatever that is…call it higher cognitive functions) is contained in less than 1 billion neurons? Probably much less given that the Chihuahua has to use some of its brain for ‘lower’ functions as well (breathing, walking, etc.).
Given the greater capacity (assumed via neuron count) can one say that a Shepherd has the greater potential for intelligence than the Chihuahua (i.e. at some point is it reasonable to assume the Chiuahua’s neurons get saturated with info where the Shepherd as capacity to spare)? I know this questions is a HUGE leap but have fun with it anyway…assume an evolutionary timewarp if need be.
I have no idea who Skoyles is or how seriously we should take this report, so I offer it merely as one data point… it could be an outlier. Anyway Skoyles writes:
and
Suggesting that maybe brain size may not be as relevant as thought. I’ve heard some arguments that surface is more important to intelligence than volume, which is why humans have more convolutions than other critters.
I think this is a gross overestimate.
Yikes! Never thought I’d suffer from brain-envy with a dog! I’ve never put my brain on the scale, but according to all the predictions I’ve heard, it should only weigh between 4 and 5 pounds.
Basically, I think all of your assumptions are screwed… but I realize you were just taking a SWAG…
The data you base the questions on are obviously fabricated and biased. Do you expect to gain ground on the problem by getting those questions answered? Since the data they are based on are specious, the conclusions will be supremely fallacious. So unless you want to determine why the fanciful dogs in your imagination have varying brain sizes, I suggest you use factual data!
My remonstration aside, I have a relevant point to add. I have read that the “center of intelligence” for birds is not the cerebral cortex but the hyperstriatum, which mammals lack; however, I am not one hundred percent confident of the veracity of this fact. If correct, it is yet another item hurled onto the heap of reasons why an interspecific comparative analysis of intelligence is inherently flawed.
All the proof you need is in an old movie, possibly titled “The Brain”? In it, David Niven is the world’s greatest criminal mastermind. The reason he is so smart is that his brain is so huge that, get this, he is unable to hold his head upright! Why that didn’t win him the Oscar is beyond me.
Add that to the hyperintelligent beings with huge lobes on Star Trek, and I’d say case closed!
Thanks for the spanking Joey and Wood…nice way to dodge the question. So caught up in pointing out my gross errors in estimation you missed the question entirely because…
It does not matter what numbers I use for this!
I never tried to pretend my numbers were anywhere close to accurate because the only relevant point is a German Shepherd’s brain is bigger than a Chihuahuas!
Feel free to correct pounds into ounces or 10X bigger to 2x bigger. Again, it does not matter in regards to what I’m asking! The only potential fallacy that would be relevant to trashing my questions is the assumption that a German Shepherd has a significantly larger brain than a Chihuahua. Given the goofy heads on Chihuahuas for all I know they may be the same size…can’t say as I’ve ever measured them myself.
Heck, forget about a German Shepherd’s brain being larger than a chihuahua’s brain… The Shepherd’s brain is probably larger than the Chihuahua, period. And Jeff’s question remains: If the brains are radically different in size, then why are their capabilities so similar? And if the small brain is enough, then why bother with a brain so much larger?
Interesting analysis. I thought I had first answered your question (see the link and quotes), then went on to point out a few technical errors.
My answer is that brain size doesn’t matter - as long as we’re talking about healthy brains. There is considerable evidence that shows that humans with significantly larger brains don’t demonstrate a measurable increase in intellect and individuals with significantly smaller brains don’t demonstrate intelligence deficits. In other words, it’s not the size that counts, it’s how you use it…
I think it was the article, above that pointed out that a number of animals (including monkeys) have a greater brain to body ratio than humans… Also, consider the example of ‘Doogie Mouse’ - these experiments showed that specific chemical reactions played a bigger role in intelligence than size…
Sorry if I came off a bit abrupt or patronizing, I was in a hurry yesterday…
