Law of Population was a treatise written  as a response to works on population growth by an English cleric and what?
Thomas Robert Malthus Thomas Robert Malthus ( ; 13 February 1766 – 29 December 1834) was an English cleric and scholar, influential in the fields of political economy and demography. Malthus himself used only his middle name, Robert.
Parson-naturalist A parson-naturalist was a cleric (a "parson", strictly defined as a country priest who held the living of a parish, but the term is generally extended to other clergy), who often saw the study of natural science as an extension of his religious work. The philosophy entailed the belief that God, as the creator of all things, wanted man to understand his creations and thus to study them by collecting and classifying organisms and other natural phenomena.