From April 8 through April 26, 1940, the Post Office Department honored five American scientists with its fourth group of the Famous Americans Series. The icon used on each stamp is unique to the branch of science represented by the honoree, whereas in the other six groups, the same icon was used for all five stamps.
In 1940, when the first-class postage rate was three cents, the only way to receive an official first-day cover of the 1-cent Audubon stamp was to apply three 1-cent stamps to a cover. Further, one of the stamps on a one-cent post card, the official rate for post and postal cards at the time, would not be permitted to be postmarked as a First Day of Issue item.
As with all seven groups, the honorees appear in birth order, with the oldest person appearing on the 1-cent and the youngest on the 10-cent. John James Audubon, born on April 26, 1785, appears first stamp, and Jane Addams, born on September 6, 1860, appears on the last. Addams was one of only two women selected to be honored in this thirty-five-stamp series.
The POD's decision to include Jane Addams, a social worker from Chicago, in the American Scientists issues stirred considerable controversy because the idea of the 'Social Sciences' was unfamiliar to the public. The public debated the names selected for the scientists group more heatedly than it did the other six groups. The contention sparked a national discussion that asked, "What is a scientist?"