Annals of the History and Philosophy of Biology

80
Annals of the History and Philosophy of Biology, Vol. 10 (2005)
Peter McLaughlin
cifically deny that this kind of generation is in any way equivocal. Thus there seems to be
more to the story than meets the eye in Harris’ Lexicon.
Since the beginnings of modern science in the early 17th century there have been two
major breeding grounds for theories about spontaneous generation: the first is the question
of the generation in the present of small organisms especially insects and intestinal
worms; the second is the question of the historical origin of life itself including larger animals.
Both sorts of questions are related at various levels, but it has been possible for
scientists to agree on the answer in one area and to disagree in the other. I shall not give
a chronicle of various theories of spontaneous generation; rather I shall use a few examples
to illustrate the conceptual problems with which such theories were dealing.
First of all I shall introduce a conceptual distinction between spontaneous generation
and equivocal generation (generatio aequivoca). This distinction is, I think, essential to an
understanding of 17th and 18th century theories of generation. Secondly, I shall illustrate
the importance of this distinction on the example of the intestinal worms of the
domesticated pig as the problem presented itself to one important biologist, J.F. Blumenbach,
near the end of the 18th century. Thirdly, I shall present and analyze the kind
of explanation of the historical origin of life proposed by G.-L.L. de Buffon in the middle
of the 18th century in order to point out the philosophical presuppositions of this
sort of theory.
Spontaneous but not equivocal
The two terms spontaneous generation and equivocal generation are often used synonymously
by historians and were also often used synonymously by scientists in the 17th
and 18th centuries – at least by those who rejected spontaneous generation. On the other
hand, a significant number of those who advocate some form of spontaneous generation
explicitly reject what they call “equivocal” generation. In fact aside from the Aristotelians
and some eclectics such as Kenelm Digby in the mid seventeenth century one can
scarcely find a serious scientist who favored equivocal generation, although many favored
spontaneous generation. So what is the difference?
Spontaneous generation is relatively straightforward: In the Aristotelian and Christian
tradition generation was as a rule sexual and living creatures had parents of the same
species. This is the position expressed above by John Ray. Generation without parents
would be irregular, exceptional, and fortuitous – but this had not always been objectionable.
In the Aristotelian tradition rules have exceptions. The world is complex and multifarious
but not necessarily deterministic. Thus in an exceptional, parentless case when an
organism arises out of organic matter (heterogenesis) or when anything organic arises out
of anorganic matter (abiogenesis), we can say that generation is spontaneous or fortuitous.
Whenever an organism arises without parents we have spontaneous generation. But
why, one might ask, does Ray insist that the parents be of the same species?
Equivocal generation is somewhat more complicated. It was considered a form of accidental,
non-lawlike generation. In logic an argument is equivocal if the meaning of a
term is changed in the course of the argument. Equivocation in generation on the other
hand occurs when the species of progeny is changed in generation. That is, whenever