It has been argued that such ignorance was once widespread and was possibly general in the history of man. In certain tribes, especially those practising cohabitation before puberty, conception may be believed to result by more or less magical means and apart from sexual intercourse. This is reinforced by the disproportion of pregnancies to the frequency of such intercourse. In the absence of sexual education in modern schools, such ignorance may persist into early adulthood, especially for those living in isolated areas.