For questions that lie between the intersection of significant mathematical problems and fundamental questions in biology.
An excerpt by Frank Hoppensteadt in Scholarpedia: Mathematical biology is a highly interdisciplinary area that defies classification into the usual categories of mathematical research, although it has involved all areas of mathematics (real and complex analysis, integral and differential systems, metamathematics, algebra, geometry, number theory, topology, probability and statistics, as well as computer sciences). The area lies at the intersection of significant mathematical problems and fundamental questions in biology. The value of mathematics in biology comes partly from applications of statistics and calculus to quantifying life science phenomena, but more importantly from the sophisticated point of view it can bring to complicated real life systems by organizing information and identifying and studying emergent structures. Mathematical scientists, and many more from physics, chemistry, engineering, and medicine have developed and used mathematical methods in biology investigations. It is difficult to grasp the broad influence mathematics has had in biology.