Erasmus Darwin (1731-1802), the grandfather of Charles Darwin, was a full-time British physician who traveled an average of 10,000 miles a year to visit patients. He was a founder of the Lunar Society of Birmingham, and a prolific inventor. Zoonomia was Darwin’s major scientific publication and the leading medical/biological book of its
day. Published in London in 1796, Zoonomia was reprinted the same year in New York, by “T. & J. Swords, printers to the Faculty of physic of Columbia College,” and again the following year by Thomas Dobson of Philadelphia. A “second edition” was published in 1803 by “Thomas and Andrews” of Boston. By 1818, a “Fourth American Edition” had been printed in Philadelphia, by Edward Earle. The continued popularity of Zoonomia over more than two decades suggests a wide readership outside of medical schools. The 1815 “Catalog of the Library of the United States” lists Zoonomia, The Botanic Garden, and Darwin’s posthumous poem, The Temple of Nature.Like his grandson, Erasmus Darwin wrote about evolution through natural selection. Chapter 39 of Zoonomia, “On Generation,” presents Erasmus’ ideas on competition, extinction, and how “different fibrils or molecules are detached from . . . the parent . . . to form” the child. The Temple of Nature goes even farther, declaring “all vegetables and animals now existing were originally derived from the smallest microscopic ones, formed by spontaneous vitality” in ancient oceans.
When I was doing research in Ashfield, Massachusetts, I was surprised to find that six Ashfield children were named “Darwin” or “Erasmus Darwin” between 1803 and 1847. Erasmus Darwin never visited America, although he was a political radical, a friend of Benjamin Franklin and a supporter of American independence. Looking a little farther, I found there are at least sixty-three towns in Massachusetts where children were apparently named after Darwin before 1849! I also found 96 towns where there’s no record of a child named “Erasmus” or “Darwin” in the Vital Records (these two groups represent all the towns whose records I was able to find online).
It’s possible that a few of the children named “Erasmus” may have been named for the fifteenth-century humanist, or for remote family members (close ones would have showed up in the records I was searching). But I think most of them were named for the scientist, especially because in many cases the children are actually named “Erasmus Darwin.” So far, I’ve found no record of “Darwin” being a family name anywhere in early nineteenth-century Massachusetts, and Charles Darwin’s only significant publication before 1849 was his The Zoology of the Voyage of H.M.S. Beagle, published in 5 parts, 1838-1843. So there’s a high probability that a lot of people in Massachusetts thought highly enough of Erasmus Darwin to name a son after him.
In all, I found 112 children named “Erasmus,” “Erasmus Darwin,” “Darwin,” or, in a couple of cases, “Erastus Darwin.” But my initial search of Vital Record books available online missed 187 towns, whose records are not yet available electronically. After my PhD work is done, I’ll try to complete the map. In the meantime, I think it’s remarkable how widely read and apparently influential the works of Erasmus Darwin were in rural Massachusetts in the early nineteenth century!
(Green = places with a "Darwin"; Brown = places without; White = haven’t got to it yet)
[See also Dan's sketches of these "Darwins" here.] 
