The more you evolve I guess there's more surface area to evolve on. Similarly cavemen could only do so much. But today you can take a degree in physics, art, history, etc. and it's probably impossible for one person to know all that ever was and is. But it's possible for a caveman shaman to know everything the tribe knew up to that point. Probably. So while it's harder to make progress there's also a lot more places you can progress.