So, yes, the columnist has a great point, a very large point, to make: biology is pretty complex and generally makes it impossible to draw neat clean lines without any ambiguity when you spend your time looking at the details. Scale matters, and emergence helps us draw lines, but only when we gaze at the appropriate scale. In the end, looking at smaller and smaller scales, emergence decoheres and identity breaks up. Not only the identity of individuals, but groups and all sorts of patterns. Without identity, there is nothing to discuss, analyze, protect or care about.
This is the problem that makes it almost impossible, if not wholly impossible, to define species, communities, individuals, alive, dead, ecosystems, and all other manner of biological entities we would like to define.
I can take any definition you give for these things and turn them on their head to the point that the original word is utterly useless. Amazing what a PhD in biology can do for ones ability to define things. I can make bacteria part of the person, an entire hive of bees a single organism, the beach part of the ocean and define away all those endangered 'species' you care so much about.
This is about as helpful as the scholastic games the collegians in Canterbury Tales are accused of, however. This sort of definitional argument has merit only when it helps us clarify function, form, predictive capacity, and moral weight. We need science to help us understand what we are doing, what we can do, what will happen when we do something, and what we should do - not to tell us that all our words are meaningless. English departments do that just fine.
We need biologists to draw dotted lines about as clearly as they can, to help us predict and sort out as well as current technology allows. The original authors who defined a person from conception have done just that. They have demonstrated the beginning of a more or less reliable developmental trajectory that is not a tumor. Sometimes it dies, sometimes it thrives. It doesn't work this way in all organisms, to be sure, particularly plants, fungi, bacteria - but also many animals that are parthenogenic, and many which are social and designate sex for a single member (like bees).
It's a difficult line, and it relies on the emergence of individuality within the new person. It is fundamentally not a mechanistic definition and is definitely only sensible in retrospect (knowing that certain processes form new individuals). It draws a clear line in otherwise murky waters and provides a foundation for moral decision that is informed by but not preempted by or dictated by, the biology.
In the end, objecting that the biology is messy is not a helpful argument - because plenty of conservative and liberal and otherwise political, moral, ethical and rhetorical positions rest on similarly drawn lines in the biology. Undrawing all the lines is a 'plague on all our houses' - an abandonment of rational thought and an abandonment of any attempts at morality, ethics and self-perpetuation as humans. Like Singer, who has confused (in the original sense of comingled wrongfully) humans and non-humans (he would lose at the game animal, vegetable and mineral, it seems), we find only a morass once we stop drawing lines. With nothing to see, analyze, protect, or care about, we lose all identity but 'I think therefore I am' and end up trapped in eternal solipsist narcissism, dehumanized because community is part of identity, and identity is part of humanity.
