APA Style originated in 1929, when a group of psychologists, anthropologists, and business managers convened and sought to establish a simple set of procedures, or style guidelines, that would codify the many components of scientific writing to increase the ease of reading comprehension. They published their guidelines as a seven-page article in Psychological Bulletin describing a “standard of procedure, to which exceptions would doubtless be necessary, but to which reference might be made in cases of doubt” (Bentley et al., 1929, p. 57).
Since then, the scope and length of the Publication Manual have grown in response to the needs of researchers, students, and educators across the social and behavioral sciences, health care, natural sciences, humanities, and more; however, the spirit of the original authors’ intentions remains.
Bentley, M., Peerenboom, C. A., Hodge, F. W., Passano, E. B., Warren, H. C., & Washburn, M. F. (1929). Instructions in regard to preparation of manuscript. Psychological Bulletin, 26(2), 57–63. https://doi.org/10.1037/h0071487
Source: American Psychological Association (2019). About APA Style.https://apastyle.apa.org/about-apa-style
In short, the changes are:
(1) MLA style, defined by the Modern Language Association, is most common in the humanities. Because humanities research highlights how one piece of writing influences another, MLA style emphasizes the author’s name and the page in the original text you’re using. This information allows scholars to track down easily the exact sentences you’re analyzing. (2) APA style, defined by the American Psychological Association, is most common in the social sciences. Although the author’s name is an important element in APA citations, this style emphasizes the year the source was published, rather than the page number, which allows a reader to see quickly how the research you’re writing about has evolved over time
Source: Poorvu Center for Teaching and Learning (n.d.) Why Are there Different Citation Styles? https://poorvucenter.yale.edu/writing/using-sources/principles-citing-sources/why-are-there-different-citation-styles