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Robert Hall
All animal life forms begin with DNA. DNA, basically, contains all cellular information for biological reproduction and growth. I understand that the process is more involved and complicated than this, but this may provide clarity to maintain simplicity. When the male and female cells unite, they become a new cell uniting both chromosomes, developing its own unique nucleus. This process now satisfies the requirements for an embryo, which is defined as: A multicellular (sperm and ovum) organism with two united DNA's, with its own unique nucleus.
At this moment, the Parent DNA of the new organism is established, with all the genetic information for development and growth of the organism through its complete life. This Parent Cell begins replicating, trillions and trillions of times. All the timing for the development of each replicated cell is in the original DNA, each cell developing its predetermined individual purpose, (eyes, heart, toes, etc.), and this information is passed on to each replicated cell.
The physical, biological, and chemical conditions will not change, unless acted upon by some outside influence, such as introduction of a drug, or an accident to the host, (mother), or abortion from an unnatural source.
Since the result is predetermined by the initial combining of the two primary DNA's, who is to determine when during those trillions of replications that a life is not present? And when would it be most favorable to interrupt this process for the purpose of trying to create another life form by cloning?