The problem, however, is precisely the opposite: If only Catholics could breed like rabbits. Given rabbit biology, and the church's restrictions on contraception, that would make "responsible parenthood" easier for the faithful to accomplish.
Rabbits have evolved so that intercourse occurs only when the female is ovulating. In humans, however, ovulation is concealed and not associated with any physical or behavioral changes. It is almost comic that the Catholic Church's approved "rhythm method" of contraception, which requires precise timing of ovulation cycles, is ideal for rabbits but not for humans.
Christian teaching about sex — Protestant as well as Catholic — has unfolded slowly. Sixteen hundred years ago, St. Augustine equated sex with Original Sin. He taught that the most virtuous thing to do was to abstain altogether, but if that was not possible then the only justification for intercourse was to procreate. It was a catastrophic misunderstanding of the way human sexuality operates, and it caused untold human torment. Fortunately, in the 20th century, first Protestant and then Catholic teaching began to recognize that most human intercourse is an expression of love, not just the urge to procreate.
In the late 19th and early 20th centuries, when reproductive scientists discovered that ovulation occurs about two weeks before a woman's menstrual period, Catholic teaching approved periodic abstinence as a "natural contraceptive," but "artificial" birth control was forbidden. Ironically, it was a Catholic obstetrician, John Rock, who built on the next scientific discovery — the way hormones control ovulation — to help develop the birth control pill.
Rock, who went to Mass every day, conducted important early tests of the pill. In 1963, he wrote a landmark book, "The Time Has Come: A Catholic Doctor's Proposals to End the Battle Over Birth Control." He pointed out that the pill's hormones imitate the natural suppression of ovulation that occurs during pregnancy and breast-feeding, and many observers expected that such reasoning would cause the Vatican to reverse its course on birth control.
In 1968, however, Pope Paul VI issued an encyclical, "Humanae vitae" (On Human Life), condemning any method of contraception "intended to prevent procreation." Its conclusions were contrary to advice of the special commission that the previous pope had launched to discuss birth control. The encyclical had little basis in theology and none in biology. As one cleric put it, it was as if the church had decided that because it had "sent all those souls to hell [for using contraception], it must keep maintaining that is where they are." "Humanae vitae" tore the Catholic Church apart. John Rock and millions of others stopped attending Mass.
Science has only continued to support Rock's idea that oral contraceptives imitate natural processes. Evolutionary biologists now believe that human females evolved to give birth perhaps four to six times total, with long periods — perhaps as much as three years — of breast-feeding as a natural contraceptive. Among our ancestors, women may have had only about 50 ovulations and menstrual cycles in a lifetime. Unless modern women use the pill, they may have more than 300.
Moreover, that much higher number of ovulations may be predisposing modern women to other diseases.
A 39-year study of 27,000 English women using oral contraceptives and 27,000 matched controls shows that women who used the pill "had a significantly lower death rate than nonusers." Nuns in particular are advised to use the pill for a couple of years for its non-contraceptive, lifelong health benefits because cancers occur at a higher rate in childless women, and using the pill early in life approximately halves the risk. The birth control pill is the only medicine I can prescribe as a physician to reduce the risk of some important cancers for women.
By contrast during the last half-century, scientific insights into Vatican-approved periodic abstinence have uncovered the possibility of an important adverse risk. When the rhythm method fails in human use, when a couple miscalculate the timing or length of ovulation, there is a greater than average possibility that the egg that is fertilized, or the sperm that does the fertilizing, will have been in the Fallopian tubes for a longer than average time. Embryos that are formed from "old" eggs or sperm are more likely to develop with birth defects.
Pope Francis' acknowledgment of the importance of "responsible parenthood" should be a catalyst for the church to reexamine its teachings. Humans evolved to have frequent sex combined with prolonged intervals of natural infertility associated with breast-feeding. We are unlikely to go back to breast-feeding a baby for three years, but we can use modern contraception to take us closer to the pattern that nature intended.
For women around the world, this is a welcome blessing. It's time to extend it to Catholics.
Malcolm Potts is an obstetrician and research scientist at UC Berkeley. He has published widely on oral contraception, breast-feeding, the history of family planning and reproductive ethics.
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