Posted on 12/02/2011 9:51:20 AM PST by BarnacleCenturion
The biological processes that occur in a corpse are well-defined, and are more or less undirected chemical reactions. Rigor mortis, for instance, occurs as a result of the depletion of ATP--the cell's main source of energy--which stops being regenerated upon death. Individual cells may remain alive after death, but without breathing and circulation, will not remain alive for long.
I really don't want to get too complicated here; self-directed (self-sustaining) biological processes are what I was referring to.
Undirected? How are they any less directed than any other chemical process? They are also no less "self-sustaining" than any other process. They are sustained just as long as necessary to accomplish their purpose, just like every other chemical process.
Exactly how much detail do you require here?
Most chemical reactions occur because the reactants are present, and the reaction is energetically favorable. Nothing directs an acid and a base to combine and become a salt: they just do that because of physical laws. Chemical reactions are not, in and of themselves, life or symptomatic of life.
Self-sustaining biological reactions occur as a result of signals that are originated in countless ways, both internally and externally (with respect to the cell). For example, a hormone molecule binding to a cell surface receptor initiates a cascade of events within the cell: gene transcription can be up or down regulated; inactive pro-enzymes can be cleaved so that they become biologically active; each of these events leads to other events. This is just a small example of the countless directed reactions that occur in a living cell and do not occur in non-living cells. For the most part, reactions within a living cell do not happen spontaneously and require an energy input.
Rigor mortis, the example of a non-living biological process that I used before, happens spontaneously and does not require energy, like any biological process that occurs post-mortem. A non-alive cell is incapable of responding to signals.
I am not certain what your purpose is in these questions. Are you genuinely looking for information, or are you looking for a way to define life that somehow excludes humans at the beginning of development? If you want information, I'm happy to provide it. But if you're looking for a "loophole" by which to scientifically exclude early stage humans from being alive, there isn't one.
Well said.
Pregnancy also begins at fertilization, in the absence of intervention. The embryo shares information with mom by chemicals/hormones before implantation.
Human intervention - or the ability to intervene - doesn’t change embryology.
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