  The idea of an economy of nature dates back at least to Linnaeus, is present throughout nineteenth century evolutionary ideas, and finds another home in Mach. Nature is an organized and frugal system. Excess exists only in a vestigial sense; everything has its place. For Darwin, the economy of nature had a ready explanation in natural selection, and the non-economical aspects of nature, such as vestigial organs, took on great significance. A logic of biology took hold: where once economy was an observed feature of nature, it now became a necessary feature. Even the apparent non-economical aspects were ultimately economical. Where once economy required explanation, it now became the explanation. A phenomenon of nature turned into a force of nature. As is typical for Mach, widely accepted biological principles become uncritically held cornerstones of his epistemology.