Human beings and all other creations have always been alive...anything made up of cells has "Life"...for when cells divide they are renewing their purpose of growth and growth is "life"...
to ask when life begins for human beings is more a philisophical or spiritual question as well as one of scientific curiosity...the joining of the egg and sperm creates the first division of the cell...scientifically that is the beginning of the renewal of life...and the cellular division continues until we have a viable human being...
the question to really ask is...when does the soul/spirit of that new being God has Created truely become just what it is...another human?
depending on ones philosophical or spiritual beliefs...it can be anytime after that first cellular division of conception...or some may even believe that we choose our "new" family in order to progress in our spiritual journey of continous learning...
