E xtravagance is a notable characteristic of human reproduction, as it is in all animal species: the majority of offspring launched at conception die before or soon after birth. For example, it is estimated that 40 percent of human pregnancies end in spontaneous miscarriage; a little more than half of these occur so early that a woman may not even realize she is pregnant.' (Major chromosomal abnormalities are a leading cause of this substantial toll in fetal life.) Many unwanted pregnancies are intentionally terminated (approximately 30 percent of pregnant women in the United States chose abortions during 19792); and an unknown number of livebom infants are neglected, abandoned, or killed before they reach the age of one month.