He then took a course in medicine at New York University, and in 1865 studied natural history under biologist Thomas Henry Huxley in London.

[2] On his return to the United States, Youmans settled at Winona, Minnesota, and practiced medicine for about three years.

[2] In 1872, he abandoned his medical practice to assist his brother in establishing the Popular Science Monthly, and subsequently was associated in editing.

[4] Youmans died of typhoid fever at his home in Mount Vernon, New York.

[4] He contributed occasionally to the pages of Popular Science Monthly under his own name, and for many years prepared the articles on chemistry, metallurgy, and physiology for Appletons' Annual Cyclopædia.