He has authored 44 scientific papers and ten high school and college biology texts.
He was granted his Ph.D. in population biology from Stanford University in 1972, his thesis being on genetic variation in alpine butterflies.
Johnson was hired as an assistant professor of biology at Washington University in St. Louis in 1972.
He was a visiting research fellow at Carnegie Institution of Washington, Department of Plant Biology, Stanford, California, 1975-1976.
During the years 1987 to 1990 he served as founding director of The Living World education center, St. Louis Zoo.