ELI5: If there are such drastic differences in intelligence between humans, how come we are all the exact same species?

There are astounding differences in intelligence between humans. A 1 in 10^100,000 chance that the smartest person in the world would have such an ungodly level of intelligence. That's a human, with the same brain, same blood and bones as the vast majority of the human population that can't even get work as a janitor. This is a person that is probably more intelligent than any human that has ever existed, including Einstein, Da Vinci, and Newton. <br><br>What is the explanation for this, and has this always happened throughout history? I don't believe that there was a single "genius" in human history, that's just not how genetics work. There were obviously many. But they lived, died, and were forgotten. <br><br>I don't believe that most people are on the same level as, for instance, Elon Musk or a neurosurgeon that can remember the details of every patient he has ever worked on, and has a photographic memory of every single body part and knows its function, down to the last neuron. We are the same species and it's hard to believe that we are even on the same planet, let alone in the same neighborhood, because we can't remember basic things like where we put down the house key or what a neuron even is.