∞PARA ΣPAR@ ` £TEXT ` ÄStevens, Nettie Maria1861╨1912biologistBorn in Cavendish, Vermont, on July 7, 1861, Nettie Stevens led an entirely obscure life for her first thirty years. In 1892 she entered the State Normal School (now Westfield State College) in Westfield, Massachusetts, where she remained for four years before transferring to Stanford University. She graduated from Stanford in 1899 and received an M.A. degree in 1900. In that year she undertook graduate studies in biology at Bryn Mawr College; during 1901 she studied at the Zoological Station in Naples, Italy, and at the Zoological Institute of the University of Wƒrzburg. She took her Ph.D. from Bryn Mawr in 1903 and remained at the college as a research fellow in biology for a year, as reader in experimental morphology for another year, and as associate in experimental morphology from 1905 to her death. In 1908╨1909 she was again in Wƒrzburg. Her earliest field of research was the morphology and taxonomy of the ciliate protozoa; her first published paper, in 1901, had dealt with such a protozoan. Later she turned to cytology and the regenerative process. One of her major papers in that field was written in 1904 with Thomas Hunt Morgan, who would later win the Nobel Prize for work in genetics. Her investigations into regeneration led her to a study of differentiation in embryos and then to a study of chromosomes. In 1905, after experiments with the Tenebrio molitor beetle, she published ╥Studies in Spermatogenesis with Especial Reference to the ╘Accessory Chromosome╒ ╙ in the Publications of the Carnegie Institution. In that paper she announced her finding that the chromosomes known as X and Y were responsible for the determination of the sex of the individual. This discovery, also announced independently that year by Edmund Beecher Wilson of Columbia University, not only ended the long-standing debate over whether sex was a matter of heredity or embryonic environmental influence but also was the first firm link between a heritable characteristic and a particular chromosome. Stevens continued her research on the chromosome makeup of various insects until her death in Baltimore on May 4, 1912. &styl ` ! ¬ 5¬ 5¬ + !I è 5¬ ï !I Æ !I ó !I
