OMFSerge at Imago Dei is providing the text of a rebuttal he used against Carl Sagan's thinking on abortion and when the unborn become "human." It's long but worth the read.
I think the most interesting part is when Sagan admits that "(t)he trouble with these particular developmental milestones (he previously named the times when an unborn child attains the ability to breathe on its own, becomes responsive to stimuli, when the face becomes distinctly "human", etc.) is not just that they're arbitrary."
He admits that these criteria are arbitrary. He then goes on to assert his own arbitrary criteria yet doesn't recognize it as such.
Sagan asserts that "If we are forced to choose a developmental criterion, then this is where we draw the line: when the beginning of characteristically human thinking becomes barely possible."
Why not fully possible? Why not totally possible? Or inherently possible? Who needs biology when we have Carl to arbitrarily choose a developmental criteria?
And what is "characteristically human thinking anyway?" Carl discusses the attainment of regular brain waves and neuron connections in the 3rd trimester but how is that "characteristically human thinking?" My newborn niece has no "characteristically human thinking" as far as I can tell. She stares into space, cries, burps, farts, looks cute, and sleeps. She's not thinking as grown humans do or even thinking at the level of toddler. If she is thinking, what's she thinking about?
On the other hand my kitten, Rascal, is deceptive and intelligent. She often exhibits thinking at a much higher level than a newborn human ever could. In the morning, Rascal uses my leg as a launching pad to get up to kitchen table so she can try to steal some of my cereal milk. She fetches in a way by bringing tiny balls of aluminum back to me to throw. She devises cheap shot attacks my other cats and then plays dead when they fight back. I've taught my other cat, Belushi, how to shake hands/paws.
It is plainly obvious to me that my cats are more intelligent than my niece is currently. Yet my niece is a human being and my cats are, well, they're cats. What tells us this? Unfortunately for Carl, it's biological facts not arbitrary developmental criteria.