The human brain hasn't changed substantially in at least 200,000 years. In terms of native intelligence, that has been the same since then.

What has changed is the availability of information. This is basically the starting point that your intelligence has the opportunity to act on.

How long did it take for someone to figure out that not only is 5 fruit more than 2 fruit, but that it is 3 more when they didn't have the concept of numbers?