Science

I'm not sure that they do. The description sounds related to how the brain is growing and organizing rather than its actual contents.

I think as a baby you can't be sure what environment you'll end up in, so evolution has packed lots of clothes for every occasion. Then by 9 you realize it's much too warm here, so we can trade away these winter jackets and collect more appropriate clothing and work out how to best sort them all. Then by your 30's you've assembled a very appropriate wardrobe and organized it the way you like. Then by your 60's the clothes are beginning to wear a bit, but we can't buy any more clothes in this analogy, so we'll have to make do. And then around 80 some things have become unusable, so we have to rely on whichever clothes proved most durable.

Exact clothes and how they're organized will vary by individual situation, but the stages of collection and sorting will be a more universal experience. At least that's how I read it.