Certainly true. Does that mean that what is ethical should be based primarily on our survival instincts?Selfless care of an infant is most certainly a natural and healthy compulsion that ensures the survival of the human race.
I think vanesch does a pretty good job in framing the question (and you guys may have read more into it than he actually said), but I'd add that people should realize that a lot of the ethical part of the debate is very straightforward: murder is illegal and immoral by definition. And virtually everyone, pro choice or pro life, agrees with that (you kinda have to - it's a definition!). Where the problem lies is determining when or by what criteria we decide when rights are to be earned/conferred. The basis for answering that question can lie in logic, science, or religion, depending on the particular person's worldview. And there is no universal agreement on when or how rights are earned/conferred, but a lot is based on semi-arbitrary age of maturity criteria: Drinking at age 21 (in the US), smoking & gambling at 18, driving at ~16, etc.