Although Charles Darwin and Gregor Mendel were contemporaries, they never met. By the 1860s. Darwin had already published The Origin of Species, assuring himself a slice of eternity and a reputation as one of history's most influential scientific thinkers. But, Mendel remained an obscure Austrian cleric, an inconsequential geneticist whose genius was not recognized until 20 years after, his death. Darwin was certainly unfamiliar with the monk's work, and Mendel has left no word of what he thought of Darwin's evolutionary theory, a theory that tried to explain the diversity and similarities among organisms, both past and present.

The two were never opponents, never contestants in a common debate. It is doubtful that either would have known if their work was related. Yet, when Mendel's work was revived in 1900, his experiments dealt Darwinism a nearly fatal blow. The popularity of Darwin's thought was already on the decline when Mendelism came into favor, but the monk's researches seemed to influence greater reproach for his theory. In 1907 a biologist named Vernon Grant had written a book citing dozens of objections to Darwin's theory and offering 24 alternate explanations of evolution. Many of his ideas sprang directly from the studies of Mendel. It seemed as if the work of two of the 19th century's greatest biologists was hopelessly irreconcilable.

Somehow. Mendel and Darwin joined forces. By 1950, their ideas were assimilated into a "modern synthesis." as Julian Huxley called it.

Ernst Mayr, Alexander Agassiz professor of Zoology emeritus, was one of the architects of this synthesis. His Systematics and the Origin of Species (1942) marked the climax of nearly three decades of work that spanned scientific disciplines and attacked the major problem left unsolved by Darwin, the origin of variation of physical features and traits among species. He and William B. Provine have outlined the development of this intellectual trend in a new book. The Evolutionary Synthesis: Perspectives on the Unification of Biology, published by the Harvard University Press.

Darwin based his theory of natural selection on the existence of this unexplained variation. He claimed varieties that were more "fit' had an advantage in competition for survival and production of offspring. However cogent his "survival-of-the fittest" theory, it was incomplete without an adequate explanation of the cause for variation.

Mendel's studies on the inheritance of physical characteristics provided the missing link for Darwin's evolutionary theory. The synthesis of their ideas required the remarkable imagination and brashness of such scientists as Wright, Haldane, Fisher, Chetverikov, Mayr, Simpson, Dobzhansky, Jepsen and others working in population genetics, systematics, cytology, and paleontology.

The unusual relationship between scientific theories that existed during this time makes the intellectual debate of this period particularly interesting. A survey of the entire history of scientific thought would probably show that most theories are either reduced, made simpler in format and broader in scope--or replaced, with another competing theory receiving wider acceptance. But important ideas are rarely "synthesized." Individual theories are rarely merged to answer a single program of interdisciplinary questions. But development in evolutionary and genetic throught from 1918 to 1947 provides an exception to this trend.

Such a synthesis cannot fairly be called a scientific revolution because it does not drastically alter the view science presents of the world. It is more a "scientific fusion," a period when old facts are looked at in new ways. That is not to say that this period was without theoretical advance, but instead that its exceptional feature was the success with which scientists removed conceptual obstacles to an understanding of how divergent biological disciplines could fit within the same theoretical framework.

New terms were introduced into the English languages deme. taxon (1950) and cline (1939) became the property of evolutionists. It was a time when Lamarckianism--the belief that acquired traits could be passed on to offspring--was finally discarded. It was a time when experimental biology replaced descriptive biology as the status science. It was a time when the study of anatomy, morphology, ecology was dropped from college curricula because it was not experimental enough, and evolutionary biology almost died here at Harvard. It was, finally, the last chapter of the Darwinian Revolution.

But besides the historical interest of this period, understanding the nature of the synthesis is important because a rival theory is currently being formulated in the rooms of the Museum of Comparative Zoology. The attack comes under many headings: "adaptationist critiques," "punctuated equilibrium," and others. But none of these names and none of these new ideas would have any meaning without the Evolutionary Synthesis which gave birth to them, without the synthesis that gave us our modern notion of where we came from and how we got here.