Annals of the History and Philosophy of Biology

82
Annals of the History and Philosophy of Biology, Vol. 10 (2005)
Peter McLaughlin
In order to clarify the problem of a spontaneous but not equivocal form of generation,
we need to introduce a few basics about normal sexual generation as this was conceived
in the early modern period. The mechanistic theories of generation of the 17th
and 18th centuries share a common basic principle that goes back to Descartes which
could be so formulated: The entire heterogeneity of the body of an organism is completely
represented materially in the germ. 2 The germ contains at least a sufficient cause
of the body if not a small model or miniature; in any case it contains a system that is alive
with the same kind of life as the later organism. The central question of the theory of the
organism was to explain the production of this germ. The two relevant alternatives in the
18th century were the (deistic) theory of pre-existing germs and the (materialistic) theory
of pangenesis, which was later replaced by the adoption of various chemical or vital
forces. Preexistence theories stipulated that all organisms arise out of germs that God
created at the beginning of the world. Within the school there were various positions
about how these germs were stored for future use – encased within one another or
spread with the winds. But there was no need or indeed room for the subsequent new
production of germs. Parentless generation is divine; subsequent generation is the unfolding
of preexisting structures that merely pass through one or both of the parents
(Roger 1997, McLaughlin 1989). In pangenesis, on the other hand, germs produce bodies,
and bodies (by pre-selecting particles) produce germs according to laws of nature –
as a rule inside one of the parents, but sometimes outside the parents.
Spontaneous Generation of Worms
Let me now take an example from the first area of spontaneous generation, the generation
of insects and intestinal worms in order to illustrate where the distinction between
spontaneous and equivocal can lead us. I shall present a problem analyzed by the German
physiologist and natural historian, Johann Friedrich Blumenbach, around 1790. We
can accept the facts and their interpretation as he presents them, since the purpose of the
example is to illustrate how to deal conceptually with the problem.
Blumenbach (1789; 1806, ch. 5) ascertains two facts which present him with an interesting
problem.
Fact 1. Domesticated pigs constitute a race descended from wild pigs within human
history. Although the two races have certain morphological differences,
there is no question that they belong to the same species.
Fact 2. Domestic pigs have intestinal worms of a species not found anywhere
else. Wild pigs do not have this species of intestinal worms. The worms of domesticated
pigs cannot survive in wild pigs.
From these facts he derives a problem.
2 Descartes [1648, 277] wrote: “If one knew exactly in detail all the parts of the seed of a particular species of
animal, for instance Man, one could deduce from that alone for reasons entirely mathematical and certain,
the whole figure and conformation of each of its parts, just as the other way around knowing some particulars
of this conformation one can deduce from this what the seed is.“