Statement 1 is incorrect: Stem cells are not derived from mammals only — they can be derived from other organisms including lower animals and plants. Statement 2 is correct: Once established, stem cells can be used to elucidate disease mechanisms and to screen drugs. Statement 3 is correct: Stem cells can be used for medical therapies — this is one of the most promising areas of stem cell research for diseases like Parkinson's, diabetes, etc.