The question of when life begins is more interesting and much more nuanced than most people think it is. Most arguments revolve around whether life begins at conception, or when the heart first beats, or at the precise moment of birth, etc. One problem with these arguments is that they all assume that life has a beginning at all.
As animals, we are entirely biased towards our diploid stage of life, ignoring the haploid stage until it comes to sex and conception. This does not apply to all living organisms, however.
Most living organisms (bacteria) do not begin lives in the traditional sense: one bacterium splits into two. Are these new lives? Did one die to give birth to two? Did one life continue while producing a new one? I do not think there is an answer – our concepts of life and death just do not apply.
There is probably little to learn from the behavior of bacteria – we are just too different. But what about plants, one of our fellow eukaryotic kingdoms?
Like us, most plants we are familiar with spend the majority of their lives in the diploid stage with haploid sperm and eggs serving the same purpose as animal sperm and eggs. However, the most “primitive” phylum of plants, the mosses, do not share this life cycle. The structures of moss that you think of when you think of moss are actually haploid. In a sense, they are akin to our sperm/eggs, but are the dominant stage of the plants’ life cycles.
While basing any moral argument on the lives of plants is folly, it is still interesting. Because of the way our life cycle is formed, we tend to see life as a series of starts and stops with birth and death. We tend to forget that we are a continuation of a cycle that has been continuing non-stop for hundreds of millions of years.
Just food for thought.