For legal policy the two most important scientific ideas of the nineteenth century were Darwinism and marginalism. Both became the starting points for the great revolutions in the social sciences that took place in the 1870s and later. The central principle of Darwinism is the theory of evolution by natural selection. Because nature produces many more offspring than each niche in the environment can accommodate, individuals of a particular species must compete to survive. Purely at random each individual acquires from its parents a set of characteristics that are different from those of any other individual. Those who inherit characteristics that give them a competitive advantage tend to live long enough to have offspring of their own. They pass these characteristics on to future generations, who then continue the struggle. The starting point for Darwinian analysis of the human individual is the environment. Both the human organism and its behavior are a product of the environment, shaped over many generations. The organism's choices are determined by the situation around it. By contrast to Darwinism, marginalism begins with the human being as an autonomous decisionmaker. Each individual has a certain amount of wealth and a collection of wants, but as his desire for some particular thing is fulfilled, his wish for more of that thing diminishes. The individual then maximizes his satisfaction by purchasing goods in such quantities so that, at the margin, the amount of satisfaction each gives him is precisely the same.
The Marginalist Revolution in Legal Thought,
46 Vanderbilt Law Review
Available at: https://scholarship.law.vanderbilt.edu/vlr/vol46/iss2/2