While religion has certainly influenced law, I’d argue (and there’s quite a bit of evidence) that social customs preceded many, if not most, of the main moral pillars of religion. So, law is not a de facto extension of religion. That said, you want science. Many anthropologists point to the advent of communal living and groups who depended on each other for survival as a step towards guarding and valuing life, beyond our own. This predates religion as we know it now.