Some here are confusing the lay meaning of theory with its scientific meaning. The lay meaning of theory is essentially hypothesis, or hunch. The scientific meaning of theory is an hypothesis supported by known evidence. Darwin's theory of evolution is fairly old and was modified in the 1930s by modern genetics and is now called the new synthesis, but people still commonly refer to the model as a whole as Darwinian evolution. The hypothetical bases of the new synthesis are supported by the known biological, physical, geological, etc., data, and so this model therefore has the status of a theory; e.g., theory in the context of a complex of hypotheses supported by observations and facts. So saying something 'is just a theory' means it has strong empirical support from observed facts, otherwise, it could not legitimately be refered to as a theory. If you want to disparage a scientific model don't say 'it's just a theory,' becuase then you are making a strong case for the model; say 'it's just an hypothesis,' that way you cast more doubt on the model: but one couldn't plausibly claim that about the Darwinian model both because of it's success in explaining biologiical phenomena and the close fit of known biological data to Darwinian principles. In contrast to Darwinian theory, intelligent design is a weak hypothesis which states that since complex information is found in genomes etc., therefore an intelligent designer must have designed them. Now the trick would be to prove these claims experimentally to strengthen the hypothesis. Intelligent design, or ID, is therefore not a theory but an hypothesis, and should not replace standard Darinian theory till it takes on the status of theory based on support by evidence based on observations.
Additionally, humans didn't come from apes, humans are apes; talking, hairless apes. Humans evolved from a proto-ape ancestor as did other apes, such as chimps and gorillas. All apes, humans, chimps, gorillas, etc., are the evolved, mutated, morphed progeny of their common proto-ape ancestor. This is why the human genome, gross morphology, and vast biochemical gene product constellation is so identical among apes and humans. In a purely scientific context, divorced from politics and traditional metaphysical beliefs, humans, chimps, and gorillas would be classified in a common genus based on morphology and genetics alone.