I call bovine manure. This is a question of embryology, PERIOD. No room for wiggle.
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(I also read your quotations from embryology textbooks, and I agree with all of them.)
The moral question, however, relating to abortion is not the same question that the embryologist were answering. The moral question is what degree of respect do we owe to a living entity. That cannot be answered from science alone, which does not address the moral question.
Consider people at the end of life. When they enter a state where the heart stops and brain waves cease, we say they are dead. Their body is still respected, but it is not protected in the same way that we would protect a healthy adult. It is buried in the ground. But at the moment of death, many cells in the body are continuing to function. Some metabolism is taking place in the muscles. It takes many minutes, maybe even hours, before every part of the body can be said to be dead. But we do not wait for that to happen before we treat the body as a dead body. In many cases, viable organs are harvested after “official” death and donated to those in need of a transplant. The characteristic that defines when this happens is the assessment of whether that person (or that body) is likely to recover to the point of being able to live normally with only “reasonable” help from others. Brain waves, a heart beat, breathing - when all of these things are absent, the person is declared dead.
…continued…