Not almost everybody alive, but certainly a very large percent. And you also have to keep in mind what this means in different eras. In the not so distant past

Not almost everybody alive, but certainly a very large percent. And you also have to keep in mind what this means in different eras. In the not so distant past the overwhelming majority of work was agrarian, any formal education was relatively rare, and issues like malnutrition were quite common. That latter aspect alone has been assessed at affecting IQ by ~15 points, enough to already send an average person into the domain of mental retardation. Go back somewhat further and drinking 'small beer', as it was called, was a frequent recommendation for young children since it was guaranteed to be relatively sterile, and had more nutrients than water. Cheers to developing brains! But if you go into the past and just look at well educated, well nourished individuals, regularly exercising their brain - then their cognitive ability was likely comparable, if not higher, than that of a typical modern era individual. But that sample made up a very small chunk of all people whereas today I'm comparing them to the norm.