“Mommy, why is the sky blue? Why do zebras have stripes? Why has Aunt Maud got hair growing out of her nose? Why are bananas crooked?” All good parents try hard to answer such questions, or at least most of them, but it is hard-core scientists who most encourage their kids to ask a lot of questions. After all, questions are a sign of curiosity, and curiosity is the ultimate, indispensable prerequisite for becoming a good scientist. Yet, as soon as the same scientists return to their labs, “why” becomes a taboo word. Why? What happens on the way to work?

Many scientists subscribe to the tenet that “why?” is not a scientific question. “How?” and “what?” are scientific questions, but “why?” is not. The famous evolutionary biologist Richard Dawkins even derided it as a “silly” question. One reason for the discrepancy is probably that children are usually satisfied with a single answer. “Bananas grow faster on one side than on the other” might just do. No need for a lecture on phototropism or auxins or other phytohormones that play a role in coordinating growth processes in plants. Not so with scientists. Every answer leads to new questions, and while many in the chain may have answers, there comes the inevitable point at which one has to admit “I don't know” or “nobody knows,” or a supernatural deity is to be evoked quasi as a deus ex machina. None of these three options is particularly desirable to scientists, and “why” is therefore a priori to be excluded from scientific discussions as a preemptive measure. Answering “why” implies that biological processes are driven by intent toward a goal; it reeks of teleology, the many-centuries-old philosophical concept that searches for the ultimate reasons of being and the purpose of human existence. It also comes uncomfortably close to questions of creationism and intelligent design, which are counter-scientific because they do not admit testable hypotheses.

If we take a detour around the semantics of the “silly why,” it does not take long to discover that scientists really do look for explanations. Thousands of studies have searched for causes of cancer or other diseases, and the investigation of just about every mechanism in biology tries to answer a question of causality. In fact, chains of causes and effects are the most prominent means of explaining biology.