Science involves Precise Description.
To be capable of being confirmed or ruled out at the high levels of reliability associated with Science, a hypothesis must be stated in a way which is precise enough to do definitive tests. Even if a scientific hypothesis may not be experimentally testable at the present time, a precise formulation helps indicate ways that it could be tested in the future. If experiment is capable of making everyone eventually agree on whether the idea worked or not, then the words it is expressed in shouldn't mean different things to different people.
Mathematical models of the physical world are the most precise form of description available, because they can describe complicated systems with perfect exactitude. In theoretical physics, this kind of quantitative description is the usual way to make things precise. We like to think about systems that are simple enough to describe mathematically (of course, this requires first making certain approximations). In fact, fundamental physics is so mathematical that, even when there are no or few experiments, one can often make progress just by demanding that the model be logically consistent, and that it conform to known physical principles. (Known, because they have been tested in other situations where we can do experiments.) Mathematical consistency is nearly our only guide in speculative fields like my own (quantum gravity); however, it cannot completely substitute for observations, since no matter how consistent or beautiful your model is, Nature could always do something else when you finally are able to take a look.
So Math is great when you can get it. Nevertheless, systems which are less regular, more complex, or less well-understood (such as biological life) cannot always be described mathematically, but may still be described through technical vocabulary that minimizes imprecision, without removing it altogether. I'm not a biologist, so I'm probably not the best person to ask how this usually works, but I didn't want to give the impression that math is the only way to make ideas precise. Even in physics, at one time it was possible to describe everything in words. The great experimenter St. Faraday (whose work helped established the concept of the electromagnetic field), once wrote a letter to St. Maxwell (who wrote down the equations for electromagnetism) expressing surprise at Maxwell's need to translate everything into mathematical equations. Yet no one could accuse Faraday's journals of being imprecise.
But not all concepts will do. Ideas that are apprehended in words or images rich with heavy associations or mottled with variegated meanings—in short, using the common language of humanity—such ideas are excluded from Science. Not because it is impossible to discuss and test these ideas; if that were true, then it would be impossible to think accurately at all about most matters of ordinary human concern. Rather, it is because they involve elements of human and holistic judgement which are unsuitable for scientific inquiry. The question “Is xenophobia a frequent cause of war?” could be given an informed and accurate answer by a historian, but it does not become a scientific question until the terms “xenophobia”, “frequent”, and “war” are given technical meanings sufficiently precise that a social scientist can do a statistical analysis.