Because of the shape of the distribution. Those who had >= 4 were sufficiently numerous for the second generation going to 3.3. P.S. also, further iteration i

Because of the shape of the distribution. Those who had >= 4 were sufficiently numerous for the second generation going to 3.3. P.S. also, further iteration is not discussed. Possibly the average for that particular curve would come down on the second or third generation.