Of course we have. Geniuses, savants, exceptional people have existed along all our history, that's the full capacity of the human brain, that's the best it can perform.
Nevertheless, the full capacity of your brain depends on genetics and training, just like, for example, your full gymnastic capacity.
Here's a very nice (slightly dated, 2012) review of the subject [1]. With it's conversational tone, it's quite a breezy read, even for non-experts. For those who are jaded of power laws and criticality being bandied about willy-nilly, this article nicely digs a little deeper.
1: https://www.frontiersin.org/articles/10.3389/fphys.2012.0016...