From Jerry Coyne:
Religious morality appears to change under only two conditions: either secular morality moves ahead of religious morality, causing it to change... or scientific advances show that the scriptural basis of religious morality is simply wrong (e.g., there’s no Adam and Eve and hence no Original Sin).
If a religion’s moral dictates remain fixed in stone for centuries, even under the press of secular advances, then that religion loses adherents. This, of course, is what is happening to Catholicism in so many places.
My comment: I agree. Consider that the vast majority of nominal Catholics do not adhere to the fundamental behavioral teachings of the Church: 98% use artificial birth control and abortion rates among Catholics are the same as society in general. Church leaders seem to look the other way in order to keep the “faithful” in the flock, although this remains a sore point among conservative, ie, orthodox, Catholics whose numbers are dwindling.
Believers, of course, will maintain that any changes in morality are "inspired" by divinity while all the observable evidence is otherwise-- that moral behavior is determined by very human desires and secular considerations.