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Dictionary of the History of Ideas

Studies of Selected Pivotal Ideas

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Spontaneous generation is the idea that life is derived
from any source other than an already existing,
genetically related parent organism. Its two main ver-
sions will be further defined as abiogenesis, or the
production of living things from nonorganic matter,
and heterogenesis, or the rise of living things from
organic matter, both animate and inanimate, without
genetic resemblance or continuity.

The idea of spontaneous generation was no doubt
first suggested by universally inaccurate observation of
how certain “lower” types of life appeared in such
environments as soil, water, and especially in decaying
organic substances. From a popular opinion seemingly
confirmed by daily experience, it passed into ancient
Greek science with only a modicum of examination.
As a rule, classical thinkers tended to attribute to
spontaneous causes of one kind or another the propa-
gation of all those vegetal and animal species about
whose sexual history the difficulties of investigation left
them in the dark. Aristotle's De generatione animalium
reflected the state of science in the fourth century, B.C.,
when it asserted that oysters, mussels, sponges, lice,
mosquitoes, flies, and some plants spring up directly
from various organic or inorganic elements. Although
spontaneous generation did not square well with his
doctrine of causality, Aristotle preferred not to ques-
tion its factualness, but rather to view it as an
“equivocal” event which, lying outside the orderly
processes of nature, understandably produced “imper-
fect” creatures. Pliny's Natural History indicates that
knowledge about the subject had not improved notice-
ably by the first century, A.D. It informs us that worms
and caterpillars are begotten from dew on cabbage-
leaves, house-flies from wet wood, maggots from rot-
ting flesh, moths from woolens, anchovies from sea-
foam, mice from river-mud, etc. General—as distinct
from scientific—literature, expressing more faithfully
popular beliefs, offered a greater number of species
imagined to be born spontaneously, and the cases that
it described were often more fantastic. Among the
favorite substances held capable of engendering life
were wood, animal-hairs, filth, excrement, stagnant
water, dried sweat, paper, and the carcasses of large
beasts. This last category in particular inspired some
curious and stubborn illusions during antiquity, for
example, that putrefaction generates hornets in dead
horses, wasps and scarabs in asses, scorpions in
crocodiles, locusts in mules, and bees in oxen. On
occasion, vertebrates were more implausibly included
among such productions, as seen in the notion that
frogs came from rainwater, or serpents from the mar-
row of the human spine! The available evidence shows
that, while spontaneous generation was unanimously
accepted as a natural principle in Greco-Roman times
and was invoked regarding many species, there was
little agreement concerning the specific cases, or the
actual manner, in which it was assumed to take place.
By its very character, such an idea was bound to un-
dergo arbitrary metamorphoses and applications.

A special version of spontaneous generation, of far
greater interest in the long run, is found in the specula-
tive tradition, launched by the Ionian cosmogonists,
that dealt with the original formation on earth of all
living things. Anaximander and Anaximenes supposed
that, in the beginning, every species had sprung into
existence from the slime of primordial seas under the
vivifying action of heat and air. This doctrine of an
initial abiogenesis was modified by Empedocles, who
taught that all creatures had evolved gradually from
chance combinations of the four elements constituting
the whole of nature. Similar opinions concerning the
emergence of men and animals from the “womb of
earth,” or from a primeval slime warmed by the sun,


found a logical place within Epicurean philosophy.
Lucretius no dobut summed up accurately this impor-
tant aspect of atomism, when in De rerum natura he
sang of how “Mother Earth” had long ago, while in
her prime, created all plant and animal species,
including man himself, immediately out of her own
substance—a creative power of which, in her tired old
age, some traces still remained in the similar generation
of certain low forms of life. Even though the thesis
of a materialistic origin for all beings drew “empirical”
support from the opinions then prevalent about the
spontaneous generation of many extant species, this
widespread and naive belief in biological spontaneity
was itself less the result of naturalistic than of animistic
habits of thought. It remained, at any rate, consonant
with the relative unawareness in antiquity that all
processes in nature obey strict and uniform laws of
physical change. The idea of spontaneous generation
will therefore go logically unchallenged until the time
when, by virtue of the seventeenth-century revolution
in science, nature will finally be stripped of its animistic
qualities and mysterious powers, and will be envisaged
as a system of exactly determined relations between
cause and effect.

Despite its antireligious uses in Epicureanism, spon-
taneous generation incurred no special disfavor with
the establishment of Christian theology. Because it was
commonly regarded as a natural fact, the Church Fa-
thers, far from condemning it as impious, were inclined
instead to adapt it to their own ends. Lactantius, for
example, adduced it as a proof of nonsexual procreation
in nature against those pagans who doubted the physi-
cal possibility of the virgin birth. Saint Augustine, in
whose City of God spontaneous generation was turned
to exegetical account, played a major role in its
“christianizing.” He sought to render more credible
the story of Noah's ark by pointing out that it had
been unnecessary to include among the species
assembled therein “very minute creatures, not only
such as mice and lizards, but also locusts, beetles, flies,
fleas, and so forth” because, in order to perpetuate all
forms of life after the Flood, “there was no need for
those creatures being in the ark which are born without
the union of the sexes from inanimate things, or from
their corruption.” The broadening of this notion per-
mitted Augustine to answer another objection regard-
ing the historical truth of the Deluge, voiced by those
who did not quite see how the account of the animals
preserved on Noah's ark could explain their subsequent
distribution in remote islands. He suggested, among
other ways in which they might have gotten there, that
“they were produced out of the earth as at their first
creation, when God said, Producat terra animam
” In the Augustinian synthesis, there was thus
no essential conflict between an original spontaneous
generation of all species and the biblical teaching of
their creation by God; on the contrary, the divine fiat,
in the absence of pre-existing parents, was the equiva-
lent of a spontaneous origin. Centuries later, Thomas
Aquinas was also able to find a place for spontaneous
generation in the all-embracing architecture of his
Scholastic theology. It was not, in fact, until the
Enlightenment that, in very different intellectual cir-
cumstances, the contradiction latent in the naturalistic
as opposed to the Scriptural meanings of creative
spontaneity came finally to the fore with far-reaching

Unhindered by Christian dogma and enjoying the
endorsement of the greatest scientific and philosophical
minds of antiquity, the doctrine of spontaneous gener-
ation lost none of its appeal and credibility during the
Middle Ages, and indeed not until the seventeenth
century. During the Renaissance, aided by the resur-
gence of animistic theories of nature, it reached, if
anything, a high point in its fortunes. Among those
at the time whose writings lent positive support to the
doctrine were Paracelsus, Ambroise Paré, G. Cardano,
A. Cesalpino, and Francis Bacon. Attesting to its
prevalence toward the end of the sixteenth century,
G. della Porta's Magia naturalis, a widely read
compendium of scientific knowledge, viewed sponta-
neous generation as an unquestionable reality, and
based the discussion of it on a long list of authorities—
even the most improbable—extending far back into
antiquity. Van Helmont was perhaps its most extraor-
dinary exponent well into the seventeenth century: a
scientist otherwise deserving of posterity's respect, he
was convinced that vermin were engendered by their
hosts, and that frogs, snails, shellfish, and the like, were
produced by the stagnant odors of marshes. One of his
recipes for the fabrication of living creatures is well
known: putrid rags stuffed in a container together with
wheat-grains will, after twenty days, give birth to mice!
It is noteworthy that until that late period those treat-
ing the subject did not, as a rule, trouble to make any
theoretical distinction between abiogenesis and
heterogenesis, it being apparently just as easy for them
to imagine the sudden emergence of life from such
inorganic substances as mud or water, as its nonrepro-
ductive derivation from organic matter, whether living
or dead.

But along with the persistence of age-old errors, the
early seventeenth century witnessed new developments
in science—particularly a growing resolve to observe
directly and experimentally the world of nature—
which were to lead to the eventual rejection of sponta-
neous generation, at least in its traditionally gross sense.
Sir William Harvey's exercitationes de generatione


animalium (1651) may be said to have represented the
modern outlook. From numerous experiments on the
mechanics of reproduction in various animal species,
he drew conclusions epitomized by the celebrated
dictum: Omne vivum ex ovo. Despite this reassuring
formula, however, Harvey did not categorically aban-
don spontaneous generation, for his rather vague un-
derstanding of both “ovum” and “omne vivum” pre-
vented him from breaking with the still current belief
in the rise of certain lower forms of life from putrefac-
tion. Yet Harvey's ovist theory, together with the
exact—and exacting—method in physiology that he
himself did so much to accredit, posed the problem
of generation in a new light by making paramount the
discovery of the “eggs” belonging to each animal spe-
cies. His dictum thus inspired the researches of
Francesco Redi, who confirmed its truth on a radically
wider scale.

Redi's Esperienze intorno alla generazione degl'insetti
(1668) is the earliest known attempt to subject the idea
of spontaneous generation to an empirical critique. His
experiments, of a lucid simplicity, were concentrated
on the case of the fly—an insect almost unanimously
held to spring from corruption. He showed that when-
ever a sample of organic matter, such as meat, was
protected from its surroundings by a gauze cloth, it
failed to produce the familiar maggots, regardless how
rotten it became. Redi perceived that, under those
circumstances, flies left their eggs on the gauze
covering, and he inferred correctly that the maggots
which ordinarily appear in putrescent substances are
nothing but the larvae of flies hatched from eggs
deposited by their parents. Redi did not repeat his
experiments with every other insect believed to origi-
nate as spontaneously as the fly, for he apparently did
not consider it necessary to do so. On the force of the
Harveyan axiom, omnia ex ovo, he assumed analogic-
ally that what was true of flies must hold true for other
insects, all of which, in his opinion, reproduced their
kind regularly by means of eggs, laid often in places
likely to mislead people into thinking that putrescence
as such has generative powers. Nevertheless, Redi did
not apply the analogy in a wholly consistent manner.
The doctrine of spontaneous generation exercising a
vestigial influence over his mind, he hesitated to con-
clude from his discoveries that it must represent in fact
something biologically impossible. Instead, he con-
tinued to accept a limited type of heterogenesis
pertaining to the presumed production of gall-insects
from living plant tissues and of parasitic worms by the
host organism. Notwithstanding such exceptions to the
rule, Redi's rejection of spontaneous generation won
rapid approval and brought about a general reversal
of scientific opinion on the subject—an outcome that
was owing not only to the value of his experimental
proofs, but also to the fact that, at the time he adduced
them, the traditional belief had already become, under
the impact of revolutionary advances in natural sci-
ence, an obvious anachronism.

Among those who, subsequently, contributed to the
further discrediting of spontaneous generation was the
great entomologist, Jan Swammerdam (1637-80). His
investigations of gall-insects, completed by Malpighi
and Vallisnieri, resulted before long in ruling out any
heterogenetical explanation of such plant parasites. His
minute anatomical descriptions made it clear, more-
over, that even the “vilest” insects exhibit marvelously
intricate structures which render the chance of their
spontaneous origin almost as nonexistent as that of the
most highly organized animals. Impressed to the point
of awe by the precise structural determinateness of all
living things, Swammerdam went in fact to the oppo-
site extreme of doubting the possibility even of
epigenesis. His theory of performation, which postu-
lated that all reproduced life must already have “pre-
existed” morphologically in the parental seed, then
succeeded so well that it dominated, in one version
or another, biological thinking for a century to come.
Under the impact of preformationism, and of the rigid
criteria of mechanical regularity and fixity that it
introduced into the entire theory of generation, the
outmoded belief in the spontaneous emergence of life
now seemed, for most biologists, to contradict the
universal laws of nature.

But concurrently with these developments, which
promised to consign spontaneous generation to the
limbo of pseudoscientific fables, the discovery by
Anthony van Leeuwenhoek (1632-1723) of the world
of microscopic organisms initiated, eventually if not
immediately, an altogether new phase in the survival
of the doctrine. The founder of protozoology was him-
self firmly opposed to the notion that his “animalcules”
could have arisen from the putrefying matter that made
up their usual environment. Having noticed the con-
jugation and fission of protozoa—without, however,
interpreting the phenomena properly—Leeuwenhoek
imagined that their offspring must result, as in the case
of more visible species, from copulation. Nevertheless,
the multitudes of micro-organisms appearing, after
only short intervals, in originally lifeless organic
infusions gave the impression of having sprung into
being literally from nowhere. Because the rate of their
multiplication was so different from the normal rhythm
of reproduction, it seemed plausible to suppose that
some extraordinary cause might be at work, such as
a transmutation process in organic matter itself. But
if the early progress of microbiology served thus to
reshape the idea of spontaneous generation into that


of microcosmic heterogenesis, it should be stressed that
the technical inability, in the seventeenth and eight-
eenth centuries, to ascertain the modes of protozoic
reproduction did not lead to the revival of the idea
on the same uncritical footing that it had known in
the pre-Radi past. Under the new scientific goal of
extending to biology the same uniformity of principles
and operations that already typified physics, it was
more commonly assumed that micro-organisms must
reproduce their own kind by processes similar to those
of the larger species. It seemed on the whole doubtful
that a mere difference in size could alter the mechanics
of generation. Furthermore, the determinism that
mechanistic science introduced into the conception of
nature made the notion of “spontaneity” itself seem
specious. To this should be added the popularity
enjoyed, in the first half of the eighteenth century, by
various “theologies of nature,” whose authors, seeking
to identify the mechanically ordered cosmos with the
providential designs of God, came to believe that
nothing expressed so well such a harmony in creation
as the preformationist view of the origin of all life.
In the perspective of this natural theologizing about
the basic problems of biology, the ancient idea of
spontaneous generation took on, for the first time,
unorthodox implications and became charged with a
naturalistic and impious potential—a fact that will
explain its special role in the Enlightenment. But while
the great majority of scientists, until around 1750, were
cautious enough—in both science and religion—to
disavow heterogenesis, the question as to how the
“animalcules” actually came into existence remained,
in an empirical sense, quite undecided.

Such was the context of the problem when John
Needham's New Microscopical Discoveries (1745)
announced that tiny eel-like creatures could be
engendered from blighted wheat-germs placed in
water. Although what he had noticed on this occasion
was only the vivifying of a type of nematode worm
deposited originally in a dry and motionless state
within the “flower” of certain grains, Needham's later
memoir (“Observations upon the Generation, Com-
position, and Decomposition of Animal and Vegetable
Substances,” 1749) defended heterogenesis on clearly
different and more far-reaching grounds. It was
claimed that microscopic organisms can be obtained
spontaneously from various infusions prepared with
mutton-gravy, macerated seeds, etc. Needham believed
that he had taken every measure necessary for steriliz-
ing and isolating his culture-media. In reality, his
methods of boiling and sealing the contents of his vials
left much to be desired. But erroneous as they were,
his observations had a considerable—and in some re-
spects positive—impact on biological science in his
day. Not only did Buffon, who had collaborated on
the same experiments, champion the new version of
spontaneous generation, but he made it the theoretical
cornerstone of his own doctrine of “organic molecules,”
by means of which he hoped to replace with an
epigenetical account of reproduction the misguided
preformationism still very much in vogue. Needham's
opinions promoted, moreover, a trend toward natural-
ism in biology, which, like other facets of eighteenth-
century philosophy, set itself in sharp opposition to
modes of thought linked with traditional metaphysics
and theology. The most striking example of this was
given perhaps by Diderot, whose Rêve de d'Alembert
(1769) used the idea of spontaneous generation as a
logically indispensable ingredient in its atheistic specu-
lations about the evolutionary origins of living forms.
The theme of spontaneous generation became in the
French Enlightenment an ideological bone of conten-
tion between materialists and antimaterialists, with a
deist such as Voltaire heaping ridicule on Needham's
“eels manufactured from paste,” and “orthodox” biolo-
gists such as Réaumur, Haller, and Bonnet forcefully
resisting the naturalistic tendency of Buffon and certain
of his followers.

In 1765, Lazzaro Spallanzani denied the hetero-
genesis of infusoria in his Osservazioni microscopiche
concernenti il sistema della generazione di Needham
e Buffon.
By subjecting his predecessors' experiments
to stricter control, he perceived that whenever a flask
containing an organic infusion and some air was
hermetically sealed and thoroughly heated, it produced
no organisms. He reasoned that Needham's infusoria
were the result less of spontaneous generation than of
imperfect sterilization. But while Spallanzani's
inference was altogether valid, it proved impossible,
given the limitations of experimental technique at the
time, to satisfy his critics. The latter objected that his
experiments were inconclusive because excessive
heating of the infusion-vial had vitiated chemically its
contents of air and organic matter, rendering them
unfit to engender or sustain life.

Owing to this impasse, biologists remained at odds
concerning the spontaneous generation of microzoa
until around 1860, when Pasteur came to the problem
from his interest in the biochemistry of fermentation,
which could not be properly investigated without first
understanding the origin and role of the varieties of
micro-organism present in fermenting liquids. Pasteur
perfected the type of experiment already performed,
though indecisively, by Schroeder and Dutsch, and
thereby ascertained that sterile culture-media remained
indefinitely free of microscopic life provided that the
“chemically unaltered” air with which they were
brought into contact had all foreign particles carefully


filtered out. From these facts he concluded that the
micro-organisms appearing after a time in sterile
infusions, and which by their multiplication cause the
latter to ferment or putrefy, come not from any vital
force in deteriorating matter, but from contamination
by “germs” floating generally in the atmosphere. The
panspermist theory was further confirmed by the inge-
nious experiments devised by John Tyndall to prove
that exposed infusions of sterile organic matter fail to
produce bacteria when surrounded by optically pure
air. Nevertheless, in the famous debate between
Pasteur and F. A. Pouchet, the latter rested his case
on two lengthy books, Hétérogénie, ou Traité de la
génération spontanée
(1859) and Nouvelles expériences
sur la génération spontanée et la résistance vitale

(1863), that described in detail numerous experiments
having results opposite to those obtained by Pasteur.
The fact that Pouchet and his co-workers, in perform-
ing essentially the same experiments as Pasteur's,
consistently observed bacterial growth under condi-
tions where their great critic could discover none, was
probably owing less to their lack of laboratory skill
than to their preference for cultures (such as hay-
infusions, where the spore of the hay-bacillus can
withstand the prolonged action of boiling water) which
could not be completely sterilized by the methods then
in use. The Pasteur-Pouchet controversy of the 1860's
also had some ideological echoes reminiscent of the
eighteenth century. But if materialists and anticlericals
tended, once again, to approve—whilst the religious
party (which included Pasteur himself) continued to
oppose—spontaneous generation, this remained a quite
secondary aspect of an issue that was eventually settled
according to strictly scientific considerations. The
banishing of heterogenesis from microbiology and the
resultant recognition that micro-organisms, like all the
more visible forms of life, are reproduced only by their
own kind, made possible the establishment of bacteri-
ology as a precise science and its revolutionary appli-
cations in immunology and in the treatment of infec-
tious diseases. Since then, whenever new experimental
claims have been made contrary to the law of bio-
genesis, such as those of H. C. Bastian in the 1870's,
it has always been possible to show, simply by improv-
ing upon Pasteur's classic methods, that spontaneous
generation does not in fact occur.

But if Pasteur and his followers disposed finally of
heterogenesis, this did not really check the career
in the modern age of another version of spontaneous
generation—that connected with the problem of
archebiosis, or the first origins of life on our planet.
In the Temple of Nature (1802), Erasmus Darwin had
set to verse his ideas on the subject: “... without
parents, by spontaneous birth,/ Rise the first specks
of animated earth./ From Nature's womb the plant
or insect swims,/ And buds or breathes, with micro-
scopic limbs.” Following Erasmus Darwin, Lamarck's
Philosophie zoologique (1809) had forged the link be-
tween a specific theory of evolution and the notion
that physicochemical forces continue even now to
produce spontaneously such rudimentary organisms as
infusoria and algae. Lamarck contended that, whereas
at present those forms of life classed above the most
elementary level reproduce themselves sexually, they
had all in effect evolved long ago from undifferentiated
prototypes which Nature, as always, is able to bring
forth “directly.” In a similar vein, but reminiscent also
of the early Greek cosmogonies, Lorenz Oken (1779-
1851) proposed the hypothesis of an Urschleim, or
primary organic substance, from which the evolution
of all species had begun presumably in the seas, and
which even now, according to him, gave rise to such
simple creatures as protozoa. Thus, during the first half
of the nineteenth century, the belief in spontaneous
generation served to promote, as it had in the previous
century, an evolutionary conception of nature.

On this aspect of the question, Pasteur's disproof of
heterogenesis was not altogether decisive and was, in
part, to be counterbalanced on a more theoretical
plane by the success of Darwinism after 1859. The
general acceptance of organic evolution on firmly
scientific grounds strengthened the assumption that the
first step in the ascent of life must have been, once
geological conditions permitted it, the formation of
some sort of primordial protoplasm from essentially
physicochemical causes—causes which, moreover,
might conceivably still be active, although much
attenuated, in the current state of the globe. Such
speculations received sensational support when, in
1867, investigation of the Atlantic floor brought to light
the mysterious Bathybius, an amorphous gelatinous
substance thought to be a sample of free-living, basic
protoplasm. Although this and subsequent claims of a
similar kind all turned out, of course, to be erroneous,
and despite the fact that before long protoplasm was
recognized to be, not a stable homogeneous mass at
all, but a highly organized dynamic system in even the
simplest cells, evolutionists could not but continue to
suppose that some type of original living entity, even
if no longer extant, had been constituted chemically
in the remote past before evolving into the complex
structures now found everywhere on earth. Among
those who, in one way or another, affirmed such a view
of archebiosis were Huxley, Pflüger, Le Dantec, Ver-
worn, Leduc, etc. In this form, moreover, the idea of
spontaneous generation was assimilated logically to
monistic or materialistic tendencies of thought. For
example, the later editions of Ludwig Büchner's Kraft


und Stoff (1855) cited the autogenesis of life as evidence
that the inherent energies of matter had alone brought
all things into existence. Ernst Haeckel, in particular,
gave crucial importance to the concept of an initial
abiogenesis in the synthesis he effected between Dar-
winism and naturalism. Positing a fundamental unity
between the realms of animate and inanimate matter,
he attributed to certain protoplasmic compounds, be-
lieved by him still to occur in nature from spontaneous
chemical reactions, the formation of monera, that is,
of what he considered to be theoretically the most
primitive individual organisms.

The status of the idea of spontaneous generation has
not changed radically in the present century. It is true
that the idea came into discussion again during the
1920's and 1930's as a result of some puzzling aspects
of virus behavior; but subsequent study of the subject
made it plain that, while viruses increase by a uniquely
parasitical process in host-cells, a pre-existing virus is
necessary to the production of new ones. Our period
has also seen various explanations proposed regarding
the manner in which life first appeared on earth, among
others that of its chance occurrence from the
polymerization of amino acids into biogenic protein
compounds. But, for obvious reasons, such conjectures
have not been verifiable. Life has not yet been
chemically synthesized in the laboratory, despite
theories about how it might have been synthesized in
the beginning by natural agents. Biogenesis—or the
rule that new life is reproduced by a pre-existing
parent—remains valid without exception, at least on
our planet. Yet it is difficult to imagine how that could
always have been the case. The idea of spontaneous
generation thus persists, as an inescapable adjunct of
organic evolution, in the postulate that transitional
prototypic modes of life once arose abiogenetically,
perhaps in different geological epochs and in more than
one place, and flourished over the long spans of time
required for the development of self-reproducing ge-
netic mechanisms. Beyond such a hypothesis, sponta-
neous generation remains a purely speculative possi-
bility. There is, for example, no categorical proof that
it is not still going on, either in its primordial or in
a modified phase, somewhere on earth. That such a
process has not yet been observed anywhere might be
attributed to its extreme infrequency, or to the imme-
diate destruction of its products by other living things.
Nor can either abiogenesis or heterogenesis be excluded
a priori with respect to some ultra-virus-like, or as yet
totally unknown, entities occupying a subvisible or
molecular level of life between the inorganic and or-
ganic worlds. In this special sense, the idea of sponta-
neous generation survives today mainly as a temptation
to expand or transcend the limits of biology.


Horacio Damianovich, La Doctrina de la generación
espontánea; su evolución y estado actual
(Buenos Aires,
1918). José Godoy Ramírez, “El origen de la vida. Evolución
de las doctrinas abiogenéticas,” Estudio, 31 (Barcelona,
1920), 355-93. Edmund von Lippmann, Urzeugung und
Lebenskraft; zur Geschichte dieser Probleme von den ältesten
Zeiten an bis zu den Anfängen des 20. Jahrhunderts
1933). Jean Rostand, La Genèse de la vie. Histoire des idées
sur la génération spontanée
(Paris, 1943).

In English: Eldon J. Gardner, History of Biology, 2nd ed.
(Minneapolis, 1965); Charles Singer, A History of Biology,
rev. ed. (New York, 1950).


[See also Biological Conceptions in Antiquity; Evolution-
ism; Inheritance through Pangenesis.]