If proposition X forbids a specific type of case from occuring, then showing that case to be "the case" would falsify that proposition. According to different websites, the theory of common descent suggests that the following are impossible: Self-pollination of a hermaphrodite flower Mutations that cause the growth of functional horns, hoofs or other traits that theory of common descent forbids will be found in humans The appearance of a new creature with no ties to its predecessors If cases such as decribed above occurs then either: 1) It was not a requirement of theory of common descent, or 2) The theory of common descent is falsified. A testable requirement of theory of common descent is what is required to be impossible by theory of common descent (in the present and in the future), to point of being NON-NEGOTIABLE. With a requirement as defined here, any instantiation of a forbidden case would NON-NEGOTIABLY require proponents to abandon the theory of common descent. In physics, abandoment happens partially, since some less accurate theories are not abandoned (e.g. Newton's theory of Universal Gravitation). So this is not about abandoning the theory completely per se, but about what cases which if they occured, would render the "theory of common descent" inaccurate at the least. The basic requirement of meaty science is not showing plausiblity, but rather showing that everything that MUST be forbidden by a theory has not occured and that therefore, such a theory is a good delimiter, or explanation, of aspects of the natural world. Without delimitation, the argument may fly against face metaphysical naturalism and suspend reason with unsubstantiated "what if" explanations. Science needs theories (especially theories of theories) which are DELIMITING. You can participate in this thread by achieving a consensus on what MUST be required (that is observable hereafter) by a theory of theories called the theory of common descent. Note that there may be multiple requirements because a single requirement would likely have further implications on what is forbidden.