Brain size found to directly correlate with intelligence

A worldwide study of the brain has found that the larger a person’s brain is, the more intelligent they tend to be.

It was found that the those with a larger hippocampus (which controls memory) have greater retention and recall. The hippocampus tends to shrink with age, which explains the poorer memory in the elderly.

Certain mental ailments, such as major depression and schizophrenia, can be seen to be a result of the shrinking of this area of the brain.

Unfortunately alcohol, poor diet and insufficient exercise can ultimately cause the same shrinkage in the hippocampus; those with a slothful lifestyle may end up literally making themselves unintelligent.

[Source]