EVOLUTION AS A SCIENTIFIC EXPLANATION FOR THE DIVERSITY OF LIFE Charles Darwin used the scientific method to propose a hypothesis for the diversity of life. Observation: There is a tremendous diversity of life on Earth. Hypothesis: The diversity of life is a result of Natural Selection: those individuals with favorable traits will leave more of their genes in the next generation (they are selected by nature to reproduce and pass on their genes). Over extended time, this may lead to new species of life and changes in existing species. Prediction: (1) If evolution occurs, we would expect organisms to change over time in an orderly progression, as they adapt to changing environments. Evidence: Fossil record provides irrefutable evidence for the transitions of life. Prediction: (2) If evolution occurs, then a tremendous amount of time is needed to produce all of the diversity of life seen today. Evidence: Studies of radioactive decay, atomic chemistry, geology provide irrefutable evidence that the Earth is over 4 billion years old, and that the age of life exceeds 3 billion years. Prediction: (3) If evolution occurs, then the mechanisms of heredity must allow for traits to be passed on from one generation to the next. Evidence: The laws of heredity are completely consistent with evolution by natural selection. In fact, evolution is an inevitable consequence of genetics. Prediction: (4) If evolution occurs, then there must be a mechanism for genes to change over time. Evidence: Mutation is a universal feature of DNA and is easily observable in nature and in the laboratory. Prediction: (5) If evolution occurs, then groups of similar organisms should share common anatomy and physiology, since they arose from a common ancestor. Evidence: Comparative anatomy and comparative physiology are entirely consistent with natural selection. Prediction: (6) If evolution occurs, then there should be evidence of past events written in the DNA of different organisms. Evidence: Studies of DNA provide perhaps the strongest evidence for evolution: closelyrelated organisms share most of their DNA, as evidence of descent from a common ancestor.