The moment where two haploid gametes come together and form a diploid zygote.

Some people would have this be where life starts. In actuality, life started 4 billion years ago.

Beleiving a haploid cell to be less human than a newborn infant has made a big mess out of abortion issues.

This moment is of interest, because it is when two sets of genetic information are merged into a new reproductive unit. At this point the physical and genetic aspects of a individual are for the most part fixed. The personality may not start to develop until around birth.