"...it is merely a theory that all human beings (rather than just the ones who hang out at Durty Nellie's) are descendants of apelike ancestors. Got that? A theory..."

Please be careful not to confuse the scientific definition of theory with the colloquial definition of theory.

In science, a theory is an explanation of the workings behind an established fact.

In colloquy, a theory can be just a fanciful notion.

For example, no one disputes the fact of gravity (if you do, try dropping your keyboard and see what happens). But, there is no good theory of gravity. In fact, a theory of gravity consistent with both relativity and quantum mechanics is the holy grail of physics. So, the theory is poor, but the fact of gravity is quite demosntrable.

Likewise, the fact of evolution is indisputable. The theory of evolution is incomplete and undergoing constant revision, but the fact is secure - just ask a Chihuahua and a Saint Bernard.