Pierre Louis Maupertuis : biography
This was anathema to Cartesians and Newtonians. An inherent tendency towards motion was an ‘occult quality’ of the kind of favoured by mediaeval scholastics and to be resisted at all costs.
Today, of course, the concept of a ‘hard’ body is rejected. And mass times the square of velocity is just twice kinetic energy so modern mechanics reserves a major role for the inheritor quantity of ‘live force’.
For Maupertuis, however, it was important to retain the concept of the hard body. And the beauty of his principle of least action was that it applied just as well to hard and elastic bodies. Since he had shown that the principle also applied to systems of bodies at rest and to light, it seemed that it was truly universal.
The final stage of his argument came when Maupertuis set out to interpret his principle in cosmological terms. ‘Least action’ sounds like an economy principle, roughly equivalent to the idea of economy of effort in daily life. A universal principle of economy of effort would seem to display the working of wisdom in the very construction of the universe. This seems, in Maupertuis’s view, a more powerful argument for the existence of an infinitely wise creator than any other that can be advanced.
He published his thinking on these matters in his Essai de cosmologie (Essay on cosmology) of 1750. He shows that the major arguments advanced to prove God, from the wonders of nature or the apparent regularity of the universe, are all open to objection (what wonder is there in the existence of certain particularly repulsive insects, what regularity is there in the observation that all the planets turn in nearly the same plane – exactly the same plane might have been striking but ‘nearly the same plane’ is far less convincing). But a universal principle of wisdom provides an undeniable proof of the shaping of the universe by a wise creator.
Hence the principle of least action is not just the culmination of Maupertuis’s work in several areas of physics, he sees it as his most important achievement in philosophy too, giving an incontrovertible proof of God.
The flaws in his reasoning are principally that there is no obvious reason why the product of mass, velocity and distance should be particularly viewed as corresponding to action, and even less reason why its minimisation should be an ‘economy’ principle like a minimisation of effort. Indeed, the product of mass, velocity and distance is mathematically the equivalent of the integral of live force over time. Leibniz had already shown that this quantity is likely to be either minimised or maximised in natural phenomena. Minimising this quantity could conceivably demonstrate economy, but how could maximising it? (See also the corresponding principles of stationary actions by Lagrange and Hamilton).
Relation to Kant
Arthur Schopenhauer suggested that Immanuel Kant’s "most important and brilliant doctrine" – contained in the Critique of Pure Reason (1781) – was asserted by Maupertuis:
Some historians of science point to his work in biology as a significant precursor to the development of evolutionary theory, specifically the theory of natural selection.Bently Glass: Maupertius, pioneer of genetics and evolution, in Glass, B., Temkin O. & Straus W.L.Jr 1959. Forerunners of Darwin 1745–1859. p51–83 Other writers contend that his remarks are cursory, vague, or incidental to that particular argument. Mayr’s verdict was "He was neither an evolutionist, nor one of the founders of the theory of natural selection [but] he was one of the pioneers of genetics". Maupertuis espoused a theory of pangenesis, postulating particles from both mother and father as responsible for the characters of the child.Mayr, Ernst. 1981. The growth of biological thought. Harvard. p328 and p646.
Bowler credits him with studies on heredity, with the natural origin of human races, and with the idea that forms of life may have changed with time.Bowler, Peter J. 2003. Evolution: the history of an idea. Berkeley, CA. p73–75