On this date, the American evolutionary biologist Rev. John Thomas Gulick was born. John Gulick continued a family tradition by attending theological school and then did missionary work in China and Japan for over thirty-five years. But he also carried on a parallel career as a naturalist and Darwinian evolutionist. Gulick had collected land snails since his teen years, and became a convert to evolutionary thinking even before reading The Origin of Species. An acute observer, he noticed that many species and varieties of snails were often restricted to very geographically-limited ranges and, as his son Addison later wrote (Scientific Monthly 18 (January 1924): 89), Gulick came
to place great emphasis upon every form of isolation or prevention of mingling, and also to emphasize the great significance for evolution of many factors that are of internal origin, such as the unknown intricacies of the process of heredity, and the effects of new choices made by the evolving creatures…
In 1872, Gulick became the first person to advance the thesis that much evolutionary change is simply a result of chance variation; in other words, variation that has no effect whatsoever on survival and reproductive success can persist in a species. He came to this conclusion when observing the incredible diversity of local populations of Hawaiian land snails (Achatinella) and their seemingly random variation under apparently identical environmental conditions.
In 1888, Gulick introduced terms for the two patterns of evolution that are observed: the term monotypic evolution (previously called transformation) – what today we define as “the change in gene frequencies within populations over generations” – and the term polytypic evolution (previously called diversification) – simultaneous processes, like the multiplication of species, manifested by different populations and incipient species. Darwin had been far more interested in diversification, particularly during the early years of his career. Jean-Baptiste Lamarck, in contrast, had been almost exclusively interested in transformational evolution. He stressed change in time, emphasizing transformation from what was commonly called the lower to the more perfect groups, but his mechanism – “use and disuse” and the “inheritance of acquired characteristics” – was, it turned out, erroneous.
George Romanes later (1897) adopted Gulick’s terminology, distinguishing between monotypic evolution as “transformation in time” and polytypic evolution as “transformation in space.” In other words, monotypic evolution deals with the “vertical” (usually adaptive) component of change in time, while polytypic evolution deals with the “horizontal” component of change. [Today, monotypic evolution is also known as "nonbranching" evolution, or anagenesis, and polytypic evolution is also known as "branching" evolution, or cladogenesis.] This insight was largely forgotten again after 1897, until it was revived during development of the synthetic theory of evolution in the 1940s.
Gulick extended his ideas to societal evolution in human beings, which he thought was dependent on altruistic motives and a spirit of cooperation.
- Ernst Mayr, The Growth of Biological Thought: Diversity, Evolution, and Inheritance ( Cambridge, MA: The Belknap Press of Harvard University, 1982) 400-1, 555.
- J.T. Gulick, “On the variation of species as related to their geographical distribution, illustrated by the Achatinellinae,” Nature 6: 222-224 (1872).
- J.T. Gulick, “On diversity of evolution under one set of external conditions,” Journal of the Linnean Society of London (Zoology) 11: 496-505 [Read before the Linnean Society on Nov. 21, 1872].
- J.T. Gulick, “Divergent evolution through cumulative segregation,” Journal of the Linnean Society of London 20: 189-274, 312-380 (1888).