Nothing else can be known to exist. Human thought, ideas, beliefs are chance movements within the brain, which itself is material. Therefore the assertion that there is some sort of Designer behind the material world, some Entity or God which is not part of that world, is purely speculative and cannot be admitted to serious intellectual or scientific discussion. It was Charles Darwin who in the mid-19th century provided the scientific foundation for naturalism. This was the contention that life forms are so complex that there had to be a Designer.
Educational theory assumes there can be no exterior source for moral values.
The intellectual establishment closes swiftly on anyone who challenges this assumption. To question evolution in the 20th century is like questioning God in the 15th. But there has been a consequence for that. Gaping holes in the theory have gone largely unacknowledged. Despite tireless effort, nothing conclusive has been found.