I echo the comments from others in saying this is a great series you've begun.
It's frustrating arguing with people who insist science cannot tell us 1) what kind of thing the human embryo is, or 2) when the life of an individual human organism begins. My standard reply is to play skeptic and say, "Gee, those are interesting claims, but what is the evidence for them? After all, the scientific case seems compelling on its face."
Well, it's no longer just the human embryo that's having its ontology called into question. According to a FOX News story, a federal court has ruled that salmon raised in fish hatcheries are a different species from those raised naturally in the wild. Yep, the court said it without a shred of proof: They're a different species.
On one hand, I'm tempted to say that in an age where unelected judges define reality according to their own personal preferences, why the heck not define fish any ol way you want. But seriously, the FOX story is right: "How do you define hatchery and naturally spawned fish as different species? There are no biological or genetic differences. The only way you can tell the fish apart is the clipped fin on hatchery fish."
I understand abortion-choicers who concede the biological facts about the unborn, but dispute that species membership alone confers value. I reject that claim, of course, but at least those offering it distinguish between their science and their metaphysics.
Not so with some secularists who insist the science of embryology isn't science at all, only religion dressed-up as science.
Okay, let them prove it. After that, we'll have the far more interesting debate over the (unsupported) assertion that theology and metaphysics don't count as real knowledge. (For more on that debate, go here and here and here.)
But let's first get the science straight. Keep after 'em, Serge.