I studied Lamarck and Spencer on evolution 50 years ago. Even then those 'theories' were shown to be inadequate and/or flawed.

During this time, Darwin's basic principles have been shown over & over to lay out how things work...even though Darwin did not have the tools to fill in all the details.

When Amos says Little Hawk is "splitting hairs", it is as close as necessary to be a 'theory' of why there is still confusion and doubt about the difference between 'fact' & 'theory'. It essentially says that a fact is a theory with so much corroborating evidence and knowledge about the details that we can CALL it a fact...like saying that water flows downhill. You could call that 'only' a theory, I guess...but it's a silly and almost useless linguistic way to talk, unless there is some special point to be made.

Today, we SEE examples of evolution at work in various systems that change on a much faster time scale than apes to humans...etc. It is as close to a fact as to make no difference.