The test of if a biological unit has 'independent life' is if it can survive in a basic sense on its own - may still need nurturing such as a kangaroo young, but that is still surviving apart from the mother. A fetus, by definition cannot. It is only with the most advanced SCIENCE and medical intervention that premature human babies can survive - all the theists were ever able to do was pray over it, which never did much but make them feel better.