William Jay Youmans was born on October 14, 1838, in Milton, New York.

He was a scientist, editor, and author. He studied chemistry at Columbia College and Yale Scientific School. He also studied natural history with Asa Fitch, and, in 1865, he took a course in medicine at New York University. Youmans continued his studies of natural history under biologist Thomas Henry Huxley (1825-1895) in London. On his return to the United States, Youmans settled at Winona, Minnesota, and practiced medicine for about three years. In 1872, he abandoned his medical practice to assist his brother Edward in establishing the Popular Science Monthly and became its editor and contributor. After his brother died in 1887, he became the editor-in-chief, remaining in that position until 1900. He also contributed articles on chemistry, metallurgy, and physiology for “Appletons' Annual Cyclopedia”. He edited Huxley's 1866 work “Lessons in Elementary Physiology”, to which he added seven chapters on hygiene, and it became the 1868 work “Elements of Physiology and Hygiene”. He also wrote, “Pioneers of Science in America” (1895). Youmans was a member of the American Association for the Advancement of Sciences.

In 1868, he married Celia Greene (1847–1915). He died from thyroid fever on April 10, 1901, in Mount Vernon, New York.