According to Chris Knight, the first humans were few; then the population "exploded Population expansion on such a scale is inconsistent with female tolerance of infanticide, harassment, or the heavy costs to mothers of male philandering and double standards. If unusually large numbers of unusually large-brained offspring were being successfully raised to maturity, the quality of childcare must have been exceptional. We know what the optimal solution would have been. There can be no doubt that mothers would have done best by taking advantage of every available childcare resource."