Born September 25, 1866, Thomas Hunt Morgan was a brilliant biologist who made and inspired numerous contributions to genetic theory in the early twentieth century, winning a Nobel Prize in Physiology/Medicine for his contributions in 1933.
After receiving his Ph.D. from John Hopkins University in 1890, Morgan became a professor at Bryn Mawr, a post which he held until 1904. Periodically throughout his employment there, he would take trips to the Zoological Station di Napoli in Europe, where he would continue his research in the field of marine biology, most notably studying embryology and the development of sea urchins. During this period of his life, Morgan was a Mutationist (one who believes in speciation by means of major mutations), quite skeptical of the prevailing Darwinian theory of evolution. He also tended to be critical of Mendel's ideas of genetics, feeling that it was impossible to accept such things without at least superficially understanding the underlying mechanisms.
In 1904, Morgan was accepted as a Professor of Experimental Zoology at Columbia University. It was here that his most famous research took place. With the help of a number of brilliant students, Morgan set up "The Fly Room", where they experimented on fruit flies in order to advance the knowledge of genetics. By means of experiments very similar to those of Mendel, Morgan discovered that some traits are sex-linked, prompting his student, Alfred Sturtevant, to construct a plausible diagram of four sets of traits, which were observed to match nicely with the four pairs of chromosomes present in fruit flies. Another student, Calvin Bridges conducted a number of experiments which conclusively proved that chromosomes are the vessel by which hereditary data is carried. This was the discovery for which Morgan would eventually receive his Nobel Prize in 1933.
Another major discovery made in the Fly Room has only been truly understood within the last couple decades. When a fly was born with two complete sets of wings, Morgan and Bridges tried mating it with other flies. Sure enough, the fly passed this mutation to its offspring. We know now that this mutation was actually the result of a change in a single gene, one of a few which happen to control the order, number, and position of all body parts. To Morgan, this was the final proof that he needed to believe in Darwin's explanation of evolution: an observable instance in which a heritable change in genes gave rise to a distinctly unique physical form.
In 1928, Morgan was invited to be the head of the Biology department at the California Institute of Technology (Caltech) by astronomer George Hale. Morgan accepted, bringing with him several of his best students. This was essentially the end of Morgan's contributions to the scientific community. He soon drifted away from genetics, focusing more on his initial interest of marine biology.
Thomas Hunt Morgan died of natural causes on December 4, 1945.