George Gaylord Simpson (1902-1984) was one of the most influential American paleontologists of the twentieth century. In the new introduction he wrote for this edition of his 1944 book, Simpson states, "My main aim was to explore and in a way to exploit the fact that paleontology is the only four-dimensional biological science: time, 'tempo,' is inherent in it. Thus the aim of this book, which I think it accomplished, was to bring this dimension squarely, methodologically, into the study of evolutionary theory." (Interestingly, he also criticizes as a "straw man" Stephen Jay Gould's interpretation of what "gradualism" in evolution means.)
Simpson argues that "Segregation or selection of intragroup variability can give rise to new groups at a potentiallly rapid evolutionary rate.... this process is important and typical in speciation and in lower levels of differentiation." He adds that "Theoretically saltation might result from a single large mutation ... or from the sudden segregation or recombination of pre-existing genetic characters."
Stephen Jay Gould and Niles Eldredge (architects of "punctuated equilibrium") were attracted to this aspect of Simpson's book: "Size of population is one of the dominant factors in determining tempo and mode in evolution," and "Thus the most rapid possible evolution must occur in populations of minimum size. Such evolution will usually lead to extinction, but in a large number of trials it will not always do so."
Such creative ideas are needed because "This regular absence of transitional forms is not confined to mammals, but is an almost universal phenomenon, as has long been noted by paleontologists." Simpson rejects, however, Goldschmidt's "hopeful monster" mechanism (proposed in his The Material Basis of Evolution: Reissued (Silliman Milestones in Science)) on the grounds that "he quite fails to adduce factual evidence that his postulated mechanism has ever produced or ever really could produce such an effect."
He proposes "quantum evolution" (defined as "the relatively rapid shift of a biotic population in disequilibrium to an equilibrium distinctly unlike an ancestral condition") as a solution, and notes that "The hypothesis that there were unusually high rates of mutation at certain times in the past ... is attractive to the point of seduction."
Interestingly, Simpson says in a footnote, "As a matter of personal philosophy, I do not here mean to endorse an entirely mechanistic or materialistic view of the life processes. I suspect there is a great deal in the universe that will never be explained in such terms and much that may be inexplicable on a purely physical plane."
This is a very significant work of interest to anyone with an interest in evolutionary theory.
A must-read for everyone studying evolution at all levels, from an undergrad student to a full professor. Many of the ideas may appear obvious to a modern reader, yet the insight of this book is tremendous.