What was the cause of the biological change in the indigenous people of St. Catherines Island after AD 1000

They became sedentary and consumed more corn, which caused dental disease due to its high sugar content.

Explanation:

nothing certain is known about what happened, but it seems that the country declined gradually, perhaps due to bad government, or, more likely, due to a series of bad harvests, which resulted in widespread and recurrent famine.

wisdom

explanation:

the fact that that the teachings on the cosmic order comes from, or through, the heart center