The individuals that are best fit to survive are more likely to reproduce and certain traits are selected for by the females such as “smart”, “tall”, “dark”, and “handsome.”
Over time this means more and more humans are born with those traits and were better at surviving than their ancestors were.
Over such large amount of time this creates millions of variants.
Lets call an ancient primate baby “Baby 1” and a primate baby born millions of years later, lets call “Baby 2.”
There comes a time when enough generations have been born to allow for the slight change in genes/traits to amount to a difference vast enough so that “Baby 1” could not have reproduced with “Baby 2.” This is the creation a new species!
This is how all of the species of plants/animals came from a common ancestor.
One of those species has to be the most advanced and it just so happens to be us in the brain department.
However there are other species that are more advanced than humans in other ways for example… the eagles eye, the octopus’ nine brains, the camouflage of the chameleon…