Too much flexibility can be a bad thing. A hypothesis that is compatible with every empirical observation (Like ID. This is also a concern I have with Theism in general) is a poor one. There has never been a theory that has agreed with every empirical observation. Never. Theories and frameworks have to take on auxiliary hypotheses. But when a theory starts to get a little too cozy with them it becomes a little troubling. Common ancestry is no where near that point. I think @Ashwin_s big misunderstanding is that he thinks common ancestry can be used to explain everything. And that’s just not true.