Analysis

Human Life Begins at the formation of a zygote, which is more commonly know as fertilization. That is the shortest and simplest explanation. Although each cell-whether sperm or ovum-is the smallest living unit. Anything living has life in it! Simple as that. I believe that human life begins at conception. Stating that the embryo or fetus becomes "alive" or "human" at a specific point is implying that it was "not human" or "not alive" before that point.
"J.T. Booner pointed out, because we consider a dog, this is a very artificial method, because what we consider an individual is usually just a brief slice of it's life cycle. When we consider a dog, for instance, we usually picture an adult. But the dog is a "dog" from the moment of fertilization of a dog egg by a dog sperm. It remains a dog even as a senescent dying hound. Therefore, the dog is actually the entire life cycle of the animal, from fertilization through death. (3)" I used this quote to illustrate that life begins at fertilization. J.T. Booner shows this using a dog but it can also be used with humans. A human will always be human from the time of fertilization till it dies. Then it is still human, it is just not living.
From a more scientific view-point, the egg begins to divide once the sperm's DNA mixes with it's own. For something to grow it needs to be alive/living. The zygote meets all the criteria for classifying a living organism. Before fertilization neither the sperm nor egg can meet these standards on their own.