Giovanni Alfonso Borelli

But gradually, biology started reorganizing itself around mathematical methods, following the Kantian principle that, quote, in every discipline of natural sciences, there is present only so much real science as there is mathematics, end quote.

By 1680, the Italian mathematician Giovanni Alfonso Borelli introduced the earliest work of biomechanics, De Motu Animalium, on animal motion.

Published just seven years before Newton's Principia Mathematica, it relies on geometry and Galilean static mechanics to explain limb movements in humans and animals, including running, jumping, swimming, and flying.

Borelli also applied his mechanical approach to basic physiological processes, such as breathing, heartbeat, blood circulation, and liver function.

His book can be regarded as the earliest formal work in theoretical biology.

A direct descendant of Borelli's line of investigation is D'Arcy Wentworth Thompson's On Growth and Form, published in 1917.

In it, the Scottish biologist and mathematician argues that biological form is a consequence of physical processes, such as crystallization, adsorption and diffusion, and of mechanical forces that constrain the evolution of organismal morphology.

Needless to say, evolutionary theory itself was also a major feat of theoretical biology and one of the most generative theoretical contributions in all of science.