Ornithology, Evolution, and Philosophy 123

348 11 History and Philosophy of Biology—Mayr’s Third Synthesis
idea of the nonfixity of species. Darwin began writing the manuscript of his big
species book in May 1856 after Lyell had urged him to publish his ideas lest he be
scooped by someone else. This indeed almost happened, when A.R. Wallace sent
Darwin a manuscript in 1858 which, in 1859, led to the publication of Darwin’s
Origin, a story recounted many times.
The “First Darwinian Revolution” of the late 19th century did not involve only
a new theory of evolution, but an entirely new conceptual world, consisting of
numerous separate concepts and beliefs. Among these are (1) an evolving rather
than a constant and created world which is, in addition, not of recent but of
great age, (2) the refutation of both catastrophism and a steady-state world, (3)
refutation of the concept of an automatic upward evolution (cosmic teleology),
(4) rejection of creationism, (5) replacement of the philosophies of essentialism
and nominalism by population thinking, and (6) the abolition of anthropocentrism;
Man was relegated to his place in the organic world. Because this intellectual
revolution entailed the rejection of at least six widely held basic beliefs,
it had a tremendous relevance outside of science causing a broad opposition to
Darwin’s theses. Opponents were especially orthodox Christians, natural theologians,
lay-persons, philosophers, physical scientists, and non-Darwinian biologists
(Mayr 1972d). Darwin’s conceptualizations affected the thinking of average people
and their worldview more than the work of Copernicus, Newton, Marx or Einstein.
Darwin’s evolutionary paradigm. Darwin’s theoretical views of evolution comprised
a set of at least five separate theses rather than one unified theory (Mayr 1982d,e,
1985j, 1991g, 1997b, 2001f who spoke of five separate “theories”):
(1) Evolution as such. This is the thesis that the world is not constant nor recently
created nor perpetually cycling but rather is steadily changing and that
organisms are transformed in time.
(2) Common descent. Thisisthethesisthateverygroupoforganismsdescended
from a common ancestor and that all groups of organisms, including animals,
plants, and microorganisms, ultimately go back to a single origin of life on
earth.
(3) Multiplication of species. This thesis explains the origin of the enormous organic
diversity. It postulates that species multiply, either by “splitting” into
daughter species or by “budding,” that is, by the establishment of geographically
isolated founder populations that evolve into new species.
(4) Gradualism. According to this thesis, evolutionary change takes place through
the gradual change of populations and not by the sudden (saltational) production
of new individuals that represent a new type.
(5) Natural selection. According to this thesis, evolutionary change comes about
through the abundant production of genetic variation in every generation. The
relatively few individuals who survive, owing to a particularly well-adapted
combination of inheritable characters, give rise to the next generation.