Daily Archives: 13 March 2014

March 13, 1720

Charles Bonnet

On this date, Charles Bonnet, a Swiss naturalist and philosophical writer, was born at Geneva, of a French family driven into Switzerland by the religious persecution in the 16th century. He made law his profession, but his favorite pursuit was the study of natural science.

Bonnet’s first published work appeared in 1745, entitled Traité d’insectologie, in which were collected his various discoveries regarding insects, along with a preface on the development of germs and the scale of organized beings. Botany, particularly the leaves of plants, next attracted his attention; and after several years of diligent study, rendered irksome by the increasing weakness of his eyesight, he published in 1754 one of the most original and interesting of his works, Recherches sur l’usage des feuilles dans les plantes; in which among other things he advances many considerations tending to show (as was later done by Francis Darwin) that plants are endowed with powers of sensation and discernment. Bonnet also studied photosynthesis in plants and noted the emission of bubbles by a submerged illuminated leaf (but see Jan Ingenhousz, who is also given credit for this observation). This very visible production of oxygen by an illuminated leaf is still used regularly in school laboratories as a way of investigating rates of photosynthesis.

Affected by his observation of the aphid, Bonnet argued, in Considérations sur les corps organisés (1762; “Considerations on Organized Bodies”), that each female organism contains within its germ cells (i.e., eggs) an infinite series of preformed individuals (Theory of Preformation), leading to an immortality and immutability of species. In his Contemplation de la nature (Amsterdam, 1764–1765; translated into Italian, German, English and Dutch), one of his most popular and delightful works, he sets forth, in eloquent language, the theory that all the beings in nature form a gradual scale rising from lowest to highest (scala natura), without any break in its continuity.

In order to explain the fossil findings of extinct species, Bonnet, in his work La Palingénésie philosophique (1769; “The Philosophical Revival”), advocated the view that Earth is periodically struck by global disasters. In these disasters most organisms die and the survivors climb the scala natura to reach new heights. According to this, mankind, the peak of evolution, would develop into angels after the next disaster, when plants would become animals, animals would become intelligent beings, and minerals would become plants. This disaster theory to explain evolution strongly influenced Erasmus Darwin (1731-1802), Charles Darwin’s (1809-1882) grandfather. This makes Charles Bonnet one of the first biologists to use the term evolution in a biological context. However, he was stuck in the preformation theory, which implied the immutability of species and precluded biological evolution.

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March 13, 1832 (a Tuesday)

Rev. John Thomas Gulick

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…

A plate of Hawaiian land snails from Addison Gulick’s book, Evolutionist and Missionary: John Thomas Gulick (1932).

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.

Darwin's illustration of an evolutionary tree, from The Origin of Species (1859).

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.

Monotypic (left) v. polytypic evolution.

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.

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