Complex sentence: It has not, and cannot, be scientifically tested as its central argument, that life forms on Earth were created by an unknown intelligent agent, introduces supernatural phenomena that can be neither proven nor disproven.
Split into simpler sentences: It has not, and cannot, be scientifically tested. This is because its central argument, that life forms on Earth were created by an unknown intelligent agent, introduces supernatural phenomena that can be neither proven nor disproven.