We underestimate the great minds of the past

As I have read about the great minds of the past in my current book - A Short History of Nearly Everything by Bill Bryson - I have come to the conclusion that the people of the past were as intelligent as the great minds of today. Yes, the general public of yesterday is much like the public of today, uneducated, but the accomplishments the intellectual of the past accomplished in math, science, and theory developed were almost breath taking. They calculated the weight of the world, the differences in longitudinal measurements, and the shape and rotation of the earth and planets in our solar system. Their calculations are so close to ours, thats its hard to believe we underestimate them so greatly. If you think about it, we aren't that much different from the world five hundred years ago. There are those who make great leaps and bounds in knowledge and advancement, and they rest of us are just 'here'.