James Kingsley Thacher

James Kingsley Thacher (October 19, 1847 – April 20, 1891) was an American professor of medicine.

His mother was Elizabeth, daughter of Yale College President Jeremiah Day.

His best known piece of work was published in 1877, and involved a criticism of Huxley and Gegenbaur on vertebrate evolution, which attracted attention both in England and Germany.

He also published other researches of value, but the demands of his practice and of the Medical School interfered seriously with the time at command for original work.

He was married, in Boston, September 10, 1878, to Emily Baldwin Foster, eldest daughter of the Hon.