A Human or non-human primate is not it's natural host, it'll probably won't work like this in it's natural reservoir (wherever that may be).
When looking at humans; in some third world countries humans reproduce even when there's not enough food available for themselves let alone their offspring. That's not really considering ones self preservation or value of life, is it?
Very complicated indeed, as you can take the "potential" concept as far as you want. (Some) Christians are for instance for the abolition of anti-conception since a potential human life will be wasted. And you could even go further by accusing a woman for not having sex after her ovulation, since the egg could've been a potential human too.
As for the question, a human life begins at conception, but I truly don't believe you can differentiate between human life and other forms of life on a "life" basis. You could however, differentiate on a "self consciousness" basis. But that would mean a human life would begin roughly between the first and second year.
On a logical basis I think YT's awnser is the best atm: when brain stem activity commences.