Nineteen schools agreed to host the scientists, but negotiating the terms of the visit was sometimes a delicate process: The goal, they assured a principal who worried about their ideological agenda, was simply to tell students why science was “cool” and perhaps interest them in a career. Still, if questions about religion and science arose, they reserved the right to answer them.

Of the 475 mid-February celebrations listed on the Web site DarwinDay.org, none had been scheduled in any of the states — Virginia, Nebraska, Montana, and Iowa — where the center’s scientists landed.