According to Lamarck 's long-discredited theory of evolution , anatomy will be structured according to functions associated with use; for instance, giraffes are taller to reach the leaves of trees . By contrast, in Darwinian evolution , form ( variation ) precedes function (as determined by selection ). That is to say in Lamarckian evolution the form is altered by the required function, whereas in Darwinian evolution small variations in form allow some parts of the population to function "better", and are therefore more successful reproductively.
Longer essays may also contain an introductory page that defines words and phrases of the essay's topic. Most academic institutions require that all substantial facts, quotations, and other porting material in an essay be referenced in a bibliography or works cited page at the end of the text. This scholarly convention helps others (whether teachers or fellow scholars) to understand the basis of facts and quotations the author uses to support the essay's argument and helps readers evaluate to what extent the argument is supported by evidence, and to evaluate the quality of that evidence. The academic essay tests the student's ability to present their thoughts in an organized way and is designed to test their intellectual capabilities.