Another problem with Sullivan’s law is that the sentence “form follows function” indicates that the relationship between the two components is unidirectional. [..] The problem is that the world doesn’t work that way. A species doesn’t feel a need first (the function) and then develop an organ to fulfill it (the form). If you’ve ever had this kind of thought—some people still do—you’ve fallen prey to what is known as the Lamarckian Fallacy.