This is a very interesting question to me for a couple of reasons. I recently got into a very heated debate with a number of people who believe that human life has no value, that it doesn't matter if a person is snuffed because there are many people alive to continue the human species.
Anyway, I think life begins AT THE LATEST conception, which plays into the abortion debate. I feel that once a female is pregnant, the baby human inside of her has as much right to life as the adult human. Actually, the baby human has MORE right to life, because the babies' life has more years. When a baby dies, 80, 90 or more years are lost. When an adult dies, less years are lost. Therefore, in my opinion, an adult life isn't as precious as a baby's life.
Of course, there is another chain of thought that life never ceases; therefore, it is impossible to pinpoint a beginning.