learning != memorization

A simple computer database has perfect memorization but zero learning ability. Learning is not the memorization of details, but rather the memory of complex abstract structural patterns.

I also find it extremely difficult to take your telephone number example seriously, when we have the oral tradition of the torah as evidence of vastly higher memory capacity.

But thats a side issue. We also have the example of savant memory. Evolution has some genetic tweaks that can vastly increase our storage potential for accurate memory, but it clearly has a cost of lowered effective IQ.

It's not that evolution couldn't easily increase our memory, its that accurate memory for details is simply of minor importance (compared for pattern abstraction and IQ).