I agree. Some of the Native Amerians from Brazil counted only up to 3, and yet their "ethnic" brethren from Central America (the Mayas) indedepently discovered the zero and precisely calculated the duration of the year. The latter were sedentary, and the former were hunter gatherers nomads, which may explain it to me to a large extent. The "ethnic" reason here does not really explain it, as they belonged basically to the same "cluster" so to say.