"And as an aside, not all people seem to see the use in developing other functions, making them act the same way all through life."

Which makes it all the more interesting.

"Everything is in a state of erosion and degeneration."

The brain's functional ability actually increases until about 20 or so, with a steep decrease in its development ocurring around 17. It then degenerates slowly after the age 25, with natural memory loss starting at age 30 or 40 I believe, although crystalized intellignece, the ability to apply one's previously learned knowledge, undergoes little degeneration until one hits their 50s, with fluid intelligence being the main recepient of said degeneration in ability.