The document discusses Karl Popper's theory of falsification and its evolution over time. It explains that Popper argued scientific theories are never truly verified, but can be falsified by a single contradictory observation. Theories should aim to be falsifiable to be considered scientific. Later, Popper acknowledged natural selection as testable despite initial doubts. The document also examines criticisms of falsification, such as that theories may not be falsified even when observations contradict them, depending on how the theory is modified in response.