Rashevsky was greatly influenced and inspired both by Herbert Spencer's book on the Principles of Biology (1898), and also by J. H. Woodger `axiomatic (Mendelian) genetics', to launch his own search and quest for biological principles, and also to formulate mathematically precise principles and axioms of biology. He then developed his own highly original approach to address the fundamental question of What is Life? that another theoretical Physicist, Erwin Schrödinger, had asked before him from the narrower viewpoint of quantum theory in biology.

In 1917, Nicolas Rashevsky joins the White Russian Navy and in 1920 he and his wife, Countess Emily had to flee for their lives to Constantinople where he taught at the American College. In 1921 they moved to Prague where he taught both special and general relativity.

From Prague, he moved in the 1930s to Paris, France, and then to New York, Pittsburgh and Chicago, USA. His life has been dedicated to the science that he founded, Mathematical Biology, and his wife Emily was very supportive and appreciative of his scientific efforts, accompanying him at the scientific meetings that he either initiated or attended.

He was awarded a Rockefeller Fellowship in 1934 and went to the University of Chicago to take up the appointment of assistant professor in the Department of Physiology. In 1938, inspired by reading On Growth and Form (1917) by D'Arcy Wentworth Thompson, he made his first major contribution by publishing his first book on Mathematical Biophysics, and then in 1939 he also founded the first mathematical biology international journal entitled The Bulletin of Mathematical Biophysics (BMB); these two essential contributions founded the field of mathematical biology, with the BMB journal serving as the focus of contributing mathematical biologists over the last 70 years.

In 1938 he published one of the first books on mathematical biology and mathematical biophysics entitled: "Mathematical Biophysics: Physico-Mathematical Foundations of Biology." This fundamental book was eventually published in three revised editions, the last revision appearing in two volumes in 1960. It was followed in 1940 by "Advances and applications of mathematical biology.", and in 1947 by "Mathematical theory of human relations", an approach to a mathematical model of society. In the same year he established the World' s first PhD program in Mathematical Biology at the University of Chicago.

Some of Rashevsky's most outstanding PhD students who earned their doctorate under his supervision were: George Karreman, Herbert Daniel Landahl, Clyde Coombs, Robert Rosen and Anatol Rapoport. In 1948, Anatol Rapoport took over Rashevsky's course in mathematical biology, so that Rashevsky could teach mathematical sociology instead.

In 1954 the budget for his Committee of Mathematical Biology was drastically cut; however, this was at least in part politically imposed, rather than scientifically, motivated. Thus, the subsequent University of Chicago administration—notably represented by the genetics Nobel laureate George Wells Beadle— who reversed in the 1960s the previous position and quadrupled the financial support for Rashevsky's Committee for Mathematical Biology research activities ("Reminiscences of Nicolas Rashevsky." by Robert Rosen, written in late 1972).

He wished to reach this `holy grail' of (theoretical/ mathematical) biology, but his heavy work load during the late 1960s—despite his related health problems—took its toll, and finally prevented him in 1972 from reaching his ultimate goal. Rashevsky's relational approach represents a radical departure from reductionistic approaches, and it has greatly influenced the work of his student Robert Rosen.

In his later years, after 1968, he became again very active in relational biology and held, as well as Chaired, in 1970 the first international "Symposium of Mathematical Biology" at Toledo, Ohio, in USA with the help of his former PhD student, Dr. Anthony Bartholomay, who has become the Chairman of the first Department of Mathematical Medicine at Ohio University. The meeting was sponsored by Mathematical Biology, Inc.

He also formed in 1969 a non-profit organization, "Mathematical Biology, Incorporated", which was to be the precursor of "The Society for Mathematical Biology", with the purpose of "dissemination of information regarding Mathematical Biology".

He cut a tall, impressive figure with a slight Russian accent, but a clear voice and thought to the very day when in 1972 he died from a heart attack caused by coronary heart disease. His generosity was very well known and is often recognized in print by former associates or visitors. As the Chief Editor of BMB he had a declared policy of helping the authors to optimize their presentation of submitted papers, as well as proving many valuable suggestions to the submitting authors.