"The net result is that slightly fewer than a third of all conceptions lead to a fetus that has a chance of developing. In other words, if you were to choose a zygote at random and follow it through the first week of development, the chances are less than one in three that it would still be there at full term, even though there has been no human intervention. Nature, it seems, performs abortions at a much higher rate than any human society. It is simply not true that most zygotes, if undisturbed, will produce a human being."