He was known for his study of plants in the Sonoran Desert, the Santa Cruz Mountains, and the Alaska North Slope, and for his history of botanical exploration in Washington, Oregon, and California.

[5] After completing his undergraduate work at Caltech, Thomas spent the next decade as an intermittent graduate student at Stanford University (MA, 1949; PhD, 1959) broken up by active military service.

[6] His master's thesis focused on the taxonomy and distribution of the evening primrose family of flowering plants in the Sonoran Desert.

[7] That same year, he joined Stanford botanist and faculty member Ira Loren Wiggins to study the plants in Point Barrow, Alaska.

From 1951 to 1952, Thomas served as an officer in the United States Navy Reserve during the Korean War after being called to active duty.

[6] Between 1965 and 1969, Thomas spent his summers as a visiting associate professor at the Flathead Lake Biological Station, a year-round, ecological research and education center run by the University of Montana.

Terman's administrative focus on these government grants led to the elimination of the Division of Systematic Biology in June 1965.

[14] In 2011, entomologists Daniel J. Bickel and Paul H. Arnaud Jr named a new long-legged fly species after Thomas (Medetera johnthomasi).

"This species is named in honor of John Thomas," they wrote in their paper announcing their discovery, "who was a great supporter of the Jasper Ridge Biological Preserve and student of its flora.

"[21] During the environmental crisis of the late 1960s and early 1970s, questions about sustainable population size became part of a public debate across the United States.

[23] That same week, he participated in the "Human Relationships in the Year 2000" symposium at Central Washington State College that brought together scientists, philosophers, religious leaders, and politicians.

Along with a variety of speakers, Thomas discussed the potential threat of a growing human population, its contribution to pollution, and its role in the destruction of the environment.

[24] He gave another talk discussing "the interrelated problems of overpopulation and pollution" at Michigan State University on October 13, 1970, where it was recorded by WKAR Radio.

[25] In March 1971, he gave the talk "The Population Component of our Current Crisis" at the annual Ojai Valley School teachers' conference.

[15] His hobbies included reading English novels by authors like C. P. Snow and Evelyn Waugh, as well as running a printing press, which he used to publish satirical reviews of work by his peers under the title Cardboard Carton Corpse and Cadaver Container Corporation.