Annals of the History and Philosophy of Biology

Spontaneous versus equivocal generation in early modern science
parents and progeny, generator and generated don’t belong to the same species of thing,
the progeny are equivocally generated. For instance, if something organic arises from
something non-organic, it is specifically different from that from which it was generated.
But also if an animal of one species gives birth to an animal of another species, we also
have a case of equivocal generation. Thus if an elephant were to give birth to a hippopotamus
or to anything that is not an elephant, generation would certainly be equivocal,
although it is hard to view it as spontaneous in any usual sense. This means that any kind
of degeneration, transformation or evolution which continues beyond the boundaries of
the species would be a form of equivocal generation, generation that is not species-true.
This sort of generation was universally rejected in the 18th century. The question is thus:
can there be spontaneous generation that is not equivocal?
Many scientists of the 17th and 18th century believed that spontaneous generation
could be unequivocal. For instance, if the same solutions, the same ingredients, always
give rise to the same species of infusoria, and different solutions give rise to different
kinds of infusoria, there seems to be nothing equivocal about this sort of generation. If
there is a lawlike connection between the ingredients mixed and the species of organisms
produced, then one could maintain (and many did) that there is nothing accidental or
equivocal about this. Far from being fortuitous, such generation is merely an instance of
matter in motion following its necessary laws, of particles combining into those structures
into which they can be organized. In the words of Descartes’ errant disciple Regius:
“Formatio illa non est fortuita sed fit ex certis et necessariis legibus motus” (Regius 1654,
224). The early atomists Pierre Gassendi, Nathaniel Highmore and Walter Charleton also
insisted that spontaneous generation was not accidental, but rather completely determined.
Highmore (1651, 83–84) criticized “equivocal generations” opposing them to the
„regular disposure” of atoms in the germ. Charleton maintained,
that those insects or spontaneous Animals have their causes certain, and by reason of that energie
once conferred upon their Efficients, must arise to animation in such and such a Figure, according
to the magnitude, number, situation, complexion, quiet, motion or in a word Temperament of those
particles, out of which their bodies are amassed; and according to the activity of that domestick
Heat, which ferments and actuate the matter (1652, 54–55). 1
Perhaps the most prominent advocate of spontaneous generation in the 18th century,
John Turberville Needham, maintained that the “vegetative force” which he introduced
to explain generation (including spontaneous generation) was constant for each species
and thus prevented generation from being equivocal:
God may have established Forces in Nature, subsisting Forces by which such Principles may in
certain Circumstances, be invariably united, without any Danger of deviating, so as to render
Generation equivocal (Needham 1748, 626).
Spontaneous (or parentless) generation can thus be considered to be just as lawlike and
unequivocal as sexual generation.
1 Gassendi (1658, 805) distinguished between animals whose seed is found in the parents and those whose
seed “is hidden in foreign and so to speak unexpected material”; the second kind are wrongly called equivocal
“because only the external and apparent cause is taken into account, not the internal hidden one.”
Annals of the History and Philosophy of Biology, Vol. 10 (2005)
81