The word 'theory' has many meanings, including: systematically organized knowledge; abstract reasoning; a speculative idea or plan; or a systematic statement of principles. Scientific theories are based on both observations of the natural world and assumptions about the natural world. They are always subject to change in view of new and confirmed observations.
This textbook discusses evolution, a controversial theory some scientists present as a scientific explanation for the origin of living things. No one was present when life first appeared on earth. Therefore, any statement about life's origins should be considered a theory.
Evolution refers to the unproven belief that random, undirected forces produced living things. There are many topics with unanswered questions about the origin of life which are not mentioned in your textbook, including: the sudden appearance of the major groups of animals in the fossil record (known as the Cambrian Explosion); the lack of new major groups of other living things appearing in the fossil record; the lack of transitional forms of major groups of plants and animals in the fossil record; and the complete and complex set of instructions for building a living body possessed by all living things.
Study hard and keep an open mind.
Now to anyone with any knowledge on the topic, it's easy to see why such a statement is incredibly misleading; doing a disservice to both science, and to the students. For a topic like evolution where there is controversy in the public arena, it's hard to explain why public controversy is not the same as academic controversy. But what if a similarly worded and toned sticker would be used on other textbooks. Take for example a book on world war 2:
The word 'theory' has many meanings, including: systematically organized knowledge; abstract reasoning; a speculative idea or plan; or a systematic statement of principles. Historical theories are based on both observations of the artefacts and assumptions about unrecorded events. They are always subject to change in view of new and confirmed observations.
This textbook discusses the holocaust, a controversial theory some historians present as a historical explanation for the genocide of the Jewish people. No one who was killed in the gas chambers survived to tell the tale. Therefore, any statement about the holocaust should be considered prone to error.
The holocaust refers to the unproven belief that there was a systematic and deliberate genocide committed by the Nazis on Jews. There are many topics with unanswered questions about the events that transpired in the concentration camp which are not mentioned in your textbook, including: the coercion Nazi officers post-WW2 into giving confessions; the lack of evidence of any explicit plan to commit such an atrocity; the lack of evidence that there was any bad treatment of the Jews by the Germans; and that there are many pieces of evidence that point to a Zionist conspiracy.
Study hard and keep an open mind.
It's important to remember that there are more historians who reject the holocaust than there are scientists who reject evolution. Once the argument is moved to another field where there's the same amount of academic controversy (i.e. essentially none) and no public controversy, the deceptiveness of the argument becomes apparent.