Robert Edmond Grant (1793 - 1874) was an Edinburgh-trained physician, who gave up the profession to study invertebrates. He was an early advocate of evolutionary thought (a strong supporter of Lamarck and his views), and cited Erasmus Darwin's Zoonomia in his medical dissertation. Darwin, while briefly a medical student (1825 - 1827) at the University of Edinburgh (following in the footsteps of his brother Erasmus, father Robert, uncle and namesake Charles, and grandfather Erasmus - although Darwin detested medical school and dropped out), was introduced to Grant through the Plinian Society, a group of students, according to Darwin, "who met in an underground room in the university of the sake of reading papers on natural science and discussing them." From their joint collecting trips to the shore, the older Grant introduced Darwin to the world of research and microscopic dissection - and this led to the Darwin's first scientific paper, delivered at the Plinian Society in 1827.
As Darwin later wrote in his autobiography, "He [Grant] one day, when we were walking together, burst forth in high admiration of Lamarck and his views on evolution. I listened in quiet astonishment, and as far as I can judge, without any effect on my mind." Later in life, Darwin would distance himself from Grant, probably because of Grant's radical views and general descent in reputation among natural historians. Nevertheless, Grant surely played a critical role in fostering Darwin's love of natural history, taste for research, and willingness to think openly about transmutation. After the publication of On the Origin of Species, Grant made sure to link his name to that of Charles Darwin, particularly through the publication of a book on the animal kingdom that he dedicated to Darwin (see images below).
Grant published a few papers that touch on evolution, in particular: On the Structure and Nature of the Spongilla friabilis (1826); On the Generative System in the Radiated or Cyclo-Neurose Classes (1834). There is considerable debate as to whether he (or Robert Jameson) anonymously authored a distinctly transmutationist 1826 paper Observations on the Nature and Importance of Geology.
For an excellent treatment of Grant and his ideas on evolution, please read: Desmond, A. 1984. Robert E. Grant: the social predicament of a pre-Darwinian transmutationist. Journal of the History of Biology 17: 189-223.