In 1878, Sigmund Freud produced his first scientific publication while a medical student in Vienna, a physiological and histological analysis of Szymon Syrski's claim to have discovered the long-sought testes of the European eel. Though he would eventually come to be known as the father of psychoanalysis, a closer look at Freud's earliest scientific publication demonstrates that he was initially positioned on the cutting edge of neo-mechanistic physiology, and academic Darwinism. Not only was the young Freud a methodologically capable physiologist, he was conceptually grounded by the anti-Lamarckian and anti-Haeckelian Darwinism of his first mentor, Carl Claus. Scholarship on Freud's life and ideas is copious and far-reaching, and yet the stature of his psychoanalytic legacy remains a significant barrier for reappraisals of his early foundations. By analyzing his first publication and the context in which it came to be, this article seeks to revisit the place of Darwin in Freud's earliest scientific work. (PsycInfo Database Record (c) 2022 APA, all rights reserved).