animal brains

My son wonders, if an animal has a small brain, does that make them not as bright as those animals which may have larger brains?
Also, do large animals have large brains?:cool:

Yes, large animals tend to have large brains, the human brain isn’t the largest in the animal kingdom.

Much is made of brain vs body volume ratio (an animal whose brain represents only 0.5% of it’s body size might be considered dim compared to another whose brain was 5%); it has a certain attractive logic to it, but I have a feeling I saw it debunked somewhere (maybe even here).

The brain isn’t an uniform organ though; different parts perform very different functions and not all animals have the same brain ‘layout’, as it were.

Brain size isn’t proportional to intellegence every time by a long shot. Some animals don’t even have real brains (like octopus), but they are well known for being very “smart”. A general answer to the question of “are animals with big brains smarter than ones with small brains?” would be “not always… it depends”. That’s the best I can do right now :rolleyes: .

Depending on how old your son is, you might want to introduce him to some of Stephen Jay Gould’s books. He’s written a few essays on this very question.

Basically, while there is a tendency for more intelligent creatures to have a higher brain/body volume ratio, it’s hard to make accurate distinctions when the sizes get close. Another big problem is deciding just what criteria to use in deciding which species is more intelligent (such as in Cecil’s column on cats vs. dogs).

You might want to also mention to him that within the same species, it becomes almost, if not completely, impossible to measure intelligence based on brain size. Human brains, for example, can vary between 900 and 2500 cubic centimeters with no difference in performance.

As an addendum to this, note that brain size for a given body size varies from type to type: a reptile will most likely have a smaller brain than a mammal of the same body size. Witness the dinosaurs: the largest ones had relatively small brains (and, in some cases, absolutely small brains - the brains of many sauropods were comparable in size to a modern dog’s).

Gould again. In his essay “Were Dinosaurs Dumb” (The Panda’s Thumb, p.259) he describes a study done to answer this question.

Looking at modern reptiles, it was found that brain size increased two-thirds as fast as body size. Extrapolating from this, James Hopson of The University of Chicago determined how big we would expect a particular dinosaur’s brain to be, based on its size, and compared to the actual size of its brain (estimated from the size of its cranium). He set this expected value as 1.0, and ranked different species by how far above or below expectations they were. From least to most brainy:

Sauropods 0.2 - 0.35 (the giant plant eaters)
Stegosaurs 0.52 - 0.56
Ceratopsians 0.7 - 0.9 (Triceratops, etc.)
Ornithopods 0.85 - 1.5 (Duckbills and other medium-sized plant eaters)
Therapods 1.0 - 2.0 (Tyrannosaurus and other large carnivores)
Stenonychosaurus 5.0 (small carnivore that ate smaller mammals and birds)

In general, it appears that brain size correlates with the challenge of catching food and evading predators.

Another thing to keep in mind is that big animals don’t necessarily need correspondingly bigger brains than smaller animals. An increase in size generally requires a few more neurons to control the extra muscle mass, but doesn’t require much more in the way of “thought”.

As Sublight points out, brain size has more to do with what the animal does than how big it is.