which biologist Ernst Mayr summarised as follows: Every species is fertile enough that if all offspring survived to reproduce, the population would grow (fact). Despite periodic fluctuations, populations remain roughly the same size (fact). Resources such as food are limited and are relatively stable over time (fact). A struggle for survival ensues (inference). Individuals in a population vary significantly from one another (fact). Much of this variation is heritable (fact). Individuals less suited to the environment are less likely to survive and less likely to reproduce; individuals more suited to the environment are more likely to survive and more likely to reproduce and leave their heritable traits to future generations, which produces the process of natural selection (fact). This slowly effected process results in populations changing to adapt to their environments, and ultimately, these variations accumulate over time to form new species (inference). Background Developments before Darwin's theory In later editions of the book, Darwin traced evolutionary ideas as far back as Aristotle; the text he cites is a summary by Aristotle of the ideas of the earlier Greek philosopher Empedocles. Early Christian Church Fathers and Medieval European scholars interpreted the Genesis creation narrative allegorically rather than as a literal historical account; organisms were described by their mythological and heraldic significance as well as by their physical form. Nature was widely believed to be unstable and capricious, with monstrous births from union between species, and spontaneous generation of life. The Protestant Reformation inspired a literal interpretation of the Bible, with concepts of creation that conflicted with the findings of an emerging science seeking explanations congruent with the mechanical philosophy of René Descartes and the empiricism of the Baconian method. After the turmoil of the English Civil War, the Royal Society wanted to show that science did not threaten religious and political stability. John Ray developed an influential natural theology of rational order; in his taxonomy, species were static and fixed, their adaptation and complexity designed by God, and varieties showed minor differences caused by local conditions. In God's benevolent design, carnivores caused mercifully swift death, but the suffering caused by parasitism was a puzzling problem. The biological classification introduced by Carl Linnaeus in 1735 also viewed species as fixed according to the divine plan. In 1766, Georges Buffon suggested that some similar species, such as horses and asses, or lions, tigers, and leopards, might be varieties descended from a common