Yost was born in Arosa, Switzerland, to Dr. Otto Friedrich Amrein and the former Anna Elisabeth Lilli Beerli, both of Switzerland. Arosa was well-know at that time for its Altein Sanatorium, a tuberculosis treatment facility. Yost's father was a prominent physician who ran the Altein for many years and made great strides in tuberculosis treatment. Otto was also an accomplished violinist and took great pride in holding chamber music rehearsals for touring musicians in his home. Yost was introduced to the violin and classical music as a small child and enjoyed both immensely throughout his lifetime. Yost attended boarding school in St. Gallen, Switzerland, where he was particularly fond of biology. Upon completion of his schooling, he traveled to Northern Rhodesia to work as a ranch manager on a citrus farm. While there, a cousin in Oxnard, CA, suggested he come to America to try citrus farming. World War II was about to begin in Europe, and since it was becoming dangerous to return to Switzerland, Yost set off for California. Always an adventurous type, he traveled the long way around, with visits to South Africa, Madagascar, Sumatra, The Great Barrier Reef, and New Zealand. Once in California, he quickly realized that it would be quite expensive to purchase a citrus ranch of his own, so he decided to continue his education and enrolled in the zoology program at UCLA. Not long afterward, the war in Europe had escalated to the point that the U.S. started to accept non-citizens in its military, so Yost enlisted in the Army Air Corps. Yost was originally trained to be a P-38 mechanic and was sent to Goose Bay, Labrador. Since there were already too many mechanics there, Yost was able to talk his way into getting assigned to the medical corp. While he was at Goose Bay, Yost was sent to Bangor, Maine where he became a U.S. citizen. In the spring of 1943, he was transferred to the Air Transport Command in Assam, northeast India, for the "Hump Operations". His unit handled amebiasis and malaria control as well as medical air rescue and evacuation. Yost was also assigned to the Army Air Force Air Transport Command Headquarters in Calcutta, where his knowledge of tropical diseases continued to increase. After the war, Yost returned to UCLA and completed his zoology degree in 1947. Because of his background in tropical medicine, he decided to pursue graduate studies in parasitology. At UCLA, he completed his M.A. in 1948 and his Ph.D. in 1951, working on trypanosomes and parasites of reptiles. His interest in invertebrate zoology, stimulated many years earlier during his trip to the Great Barrier Reef, reached a high point in 1950 when he took courses at Hopkins Marine Station. In the fall of 1951, he took a sabbatical replacement position at Pomona College, in Claremont, CA, and was offered a permanent position in Zoology the following spring. During the first two years at Pomona, he taught eleven different courses, including: Introductory Zoology (his favorite); Microbiology, Parasitology, and the History of Biology. Within eight years, Yost had risen to be the Chairman of the Zoology Department. From 1960 until his retirement in 1981, he held the Halstead Professorship of Zoology. He also had received the R.J. Wig Award for distinguished teaching, three times. In 1957, he received a fellowship from the National Institute of Health to study the biochemical genetics of parasitic protozoans on trypanosomes at the National Institute of Medical Research in London. He was further honored by being named a Fellow of the Royal Society of Tropical Medicine and Hygiene. From 1964-1965, he held a second sabbatical fellowship at the Swiss Tropical Institute where he worked on the infectivity of African trypanosomes. His other major professional society memberships include: Phi Sigma, UCLA 1951; Fellow, American Association for the Advancement of Science; Full Member, Sigma Xi; American Society of Parasitologists; Southern California Parasitologists, President 1959; and Western Society of Naturalists, Secretary 1959 and 1960, President 1969. Yost had many interests and passions during his amazing lifetime. He was fluent in five languages and traveled extensively. He adored classical music and was an exceptional violinist who once played with a college symphonic orchestra and several chamber music groups. He loved reading, hiking, animals, and working in his yard in Claremont. Ships and trains were other passions and his knowledge of and experience with them was quite vast. He held longtime memberships in the Steamship Historical Society, the Pacific Railroad Society, and the Orange Empire Railway Museum. His once ambitious and active lifestyle was abruptly taken away from him around 2000, first with the declining health of his beloved wife, Maggie, and then with his own failing heart. He was truly a one-of-a-kind person with a heart of gold and an unforgettable smile. At his insistence, there were no memorials or services.