This article has been peer-reviewed under the direction of Professors Mary Elizabeth Leighton and Lisa Surridge (University of Victoria). It forms part of the Great Expectations Pregnancy Project, funded by the Social Sciences and Humanities Research Council of Canada. [Click on the image to enlarge it.]

In the sciences, the Victorian period is most famous for producing Charles Darwin and the theory of evolution. Darwin rejected the idea that God intervened in the creation and development of life, which he saw as "inexplicable" by the "ordinary view of creation" (361). As he wrote, only the theory of descent with modification (evolution by natural selection as we know it today) can explain them. But what did Darwin mean by the "ordinary view of creation"? In general terms, this phrase referred to the Biblical creation account in which God created the world in seven days and, further, the idea that the world and its inhabitants are the same now as they have always been. Darwin's controversial theory profoundly affected the Victorians, including Alfred Lord Tennyson. However, the conflict between science and religion, particularly in relation to questions about life, started with Aristotle. In the medieval period, a Christianized version of Aristotle's theory was the dominant view until roughly the seventeenth century, when a conflict emerged between competing theories of embryology, a theory that attempts to explain how and when life begins and how the fetus develops over time in the womb (gestation).

The two main theories of embryology, preformation and epigenesis, emerged from (1) competing worldviews about God's role in creating life and (2) many scientists' desire to explain natural phenomena with material, verifiable evidence. Preformationists argued that God, the external, immaterial source of life, creates fully formed beings before or shortly after conception; in the womb, these pre-formed beings simply grow larger over time. Epigenesists, by contrast, said that life comes from an internal, material source, not an external source such as God; beings begin as unformed masses of material that develop part by part over time.

Before the Victorian period, the central questions in embryology were, How does the individual organism begin? How does it develop over time? and What drives this process? For Victorians, these questions were replaced by another: What is the relationship between the development of the individual organism (ontogeny) and that of the species (phylogeny)? The answers had important theological implications, challenging many long-held beliefs about the relationship between God and humanity.

Ancient and Medieval Backgrounds

Before the seventeenth century, most scientists and the Western European public accepted a Christianized version of Aristotle's embryology, which was essentially epigenetic. According to Aristotle, male and female seed mix and beings develop from unformed to formed masses of material "epigenetically, gradually, and internally" (Fagan and Maienschein). Aristotle believed that the male seed was the creative, active force whereas the female was inferior and passive. In Aristotle's complex, pre-Christian view, everything has a soul that is defined by that being's properties and purpose. Souls have a clear hierarchy: vegetables have nutritive souls (they can grow); animals have nutritive and sensory souls (they can grow and feel); humans have nutritive, sensory, and rational souls (they can grow, feel, and think) (Haskett et al). Concerning the agent causing form and material to create an embryo, Aristotle wrote, "Either it is something external which makes them or else it is something existing in the seminal fluid and the semen; and this must either be soul or a part of a soul, or something containing soul" (qtd. in Needham 46). He concluded that the soul is internally sourced, and the being's form develops gradually over time.

Shortly before the Middle Ages (5001500), St. Augustine (394-430) offered a Christianized version of Aristotle's embryology, which was widely accepted by the Catholic Church and Western Christians (Brind'Amour, "St. Augustine"). Augustine and later St. Thomas Aquinas (c. 1225-74) maintained that life enters the fetus at conception, but that the fetus does not become fully human until further along in gestation (Brind'Amour, "St. Thomas Aquinas"). This view aligned in some ways with ideas of hominization (becoming human) and ensoulment (the act of the soul entering the body). Importantly, Christians considered the soul as provided by God and separate from the material body. As a result, both Augustine and Aquinas believed abortion was wrong but considered it more wrong later in fetal development. Medical and popular theories of conception and human development were roughly the same as Aristotle's: the fetus starts as an unformed mass of material that gradually develops into a formed being with a purpose, a being shaped by God's will. This theory was espoused by the popular sex manual Aristotle's Masterpiece (not actually written by Aristotle), which went through hundreds of editions and versions into the twentieth century, the first in 1684 and the last in 1925 (see "Sexual Knowledge in Print Culture" by Sarah Bull.

Aristotle's Masterpiece offered a Christianized version of Aristotle's theory, maintaining some of his basic premises regarding species and gender hierarchy. It explains conception thus:

[the generation of] Man consists of an egg, which is impregnated in the testicles [ovaries] of the woman, by the more subtle parts of the man's seed; but the forming faculty and virtue in the seed is a divine gift, it being abundantly imbued with vital spirit, which gives sap and form to the embryo, so that all parts and bulk of the body, which is made up in a few months and gradually formed into the likely figure of a man, do consist in, and are adumbrated thereby. [Anonymous]

The basic concept is epigenetic: the male seed unites with the female egg, and an outside "vital spark" guides the process. The next paragraph describes stages of development from unformed material to a fully formed fetus, reflecting epigenetic theory. As noted above, the process is divinely driven. Like Aristotle's, this text supports epigenetic development; unlike Aristotle's, it gives power to God. In Aristotle's Masterpiece, the soul "is the infused breath of God, immediately proceeding from Him." The text identifies different moments when the soul enters the fetus: "Most males are perfect by the thirtieth day, but females seldom before the forty-second or forty-fifth day, because the heat of the womb is greater in producing the male than the female. [A] woman going with a male child quickens in three months, but going with a female, rarely under four." According to the text, male fetuses become "ensouled" (i.e., fully human) earlier than female fetuses, thus justifying (to some degree) abortion in the first trimester. (This text also promulgated popular ideas about sex, relationships and marriage, and medical cures, including the belief that the maternal imagination can affect the fetus.)

Pre-Victorian Backgrounds: Preformation and Epigenesis

homonculus from Hartsoeker's 'Essay de dioptrique'

Image of the homonculus from Hartsoeker's Essay de dioptrique (1694), from the Wellcome Collection.

In the mid-seventeenth century, the concept of preformation entered scientific discourse. At the time, this process was called "evolution" or "gradual unfolding," a completely different concept than Darwin's meaning of the word "evolution." Preformationists believed that God had predetermined the number of beings of each species since the creation of the world (as in Genesis) and that no being exists without a purpose for itself within the larger system. The pre-formed human being was also known as the homunculus, miniature, or germ. Preformationists argued about whether this being resided in the male sperm or the female egg. Charles Bonnet (1720-93) and Albrecht von Haller (1708-77) were proponents of ovist preformation, which speculated that these complete, microscopic human beings resided in the female egg (the ovum). The other theory, depicted on the left, which lost favor by the second half of the eighteenth century, was spermism or animalculism, which suggested that the germ resides in the male sperm. This illustration from Essay de dioptrique [Essay on Optics] [1694] by Nicolas Hartsoeker [1656-1725] depicts the homunculus inside the sperm, which Hartsoeker never claimed to have seen under the microscope but which he speculated existed based on the theory of preformation. Later, both Bonnet and Haller accepted this theory partly due to faith. In 1762, Bonnet wrote ecstatically of the beauty of preformationist explanations: "The different orders of infinitely small [beings] nested with one another that this hypothesis allows, overwhelms the imagination. I could not bring myself to abandon a theory so beautiful as that of the preexisting germs just to embrace purely mechanical explanations" (qtd. in Müller-Sievers, 27-28). In 1766, Haller explained preformation in more precise religious terms: "[God] has arranged the brute matter according to foreseen ends and according to a model preformed by his Wisdom" (qtd. in Roe, 4344). Both Haller and Bonnet concluded that only God could create the harmony and unity exemplified by preformation. Later scientists, including Darwin, no longer felt the need to articulate God's role in the process.

By contrast, epigenesists were committed to scientific principles and observable evidence, rejecting the idea of external or supernatural forces and instead attempting to identify internal material principles to explain the gradual development of unformed material to fully formed beings. The most influential epigenesists of the period attempted to explain the source of life without resorting to vitalism, a concept suggesting that life is created by something beyond the chemical or physical. Supported by natural philosophers such as Georges-Louis Leclerc, Comte de Buffon (1707-88), C. F. Wolff (1735-94), and J. F. Blumenbach (1735-94), epigenesis posits that at conception the fetus begins as a small bit of material, gradually developing organ by organ until a perfect being is formed. Buffon rejected the idea that the creation of life is "an immediate effect of the Almighty's will" (289), asserting that "experience [is] the sole source of all real science" (334). Buffon challenged preformationist theories as founded on "moral affinities which far from producing any physical or real existence only alter the reality and confound the objects of our sensations, perceptions and knowledge, with those of our sentiments, our passions and our wills" (336). In short, Buffon accused preformationists of religious bias in interpreting evidence.

More often than not, "those who accepted epigenesis also accepted a form of vitalism" (Fagan and Maienschein) because they could not physically locate the power that begins or drives the process. Buffon reasoned that "living organic particles" (279) were driven to the appropriate place by "penetrating powers" (302). In Theory of Generation (1759), Wolff posited an "essential force" that guided organic matter or "nutritive juices" (Müller-Sievers 38). Blumenbach attempted to escape this problem of vitalism by positing that a "formative drive" caused the material to form into particular organs. He equated this "formative drive" with life forces such as irritability and sensibility, an argument not unlike Buffon's "penetrating powers." Preformationists were scandalized by such ideas because, if life were simply matter and motion, then what was God's role? They also argued that epigenesis could not explain the universe's harmony. If life is simply material, there would be many chances for this process to go awry.

Although Blumenbach tried to explain the process by referring to the "formative drive," he ultimately said that this force was unknowable: it is "a power, the constant agency of which we ascertain by experience, whilst its cause, like that of all other generally recognized natural powers, still remains, in the strictest sense of the word 'qualitas occulta'" (qtd. in Müller-Sievers 43). In other words, this power is unknowable.

By early in the nineteenth century, epigenesists had won the debate between epigenesis and preformation, and other questions became more central. According to Stephen J. Gould, a shift in thinking about the world from static to progressive, from mechanical to organic, and from first causes to teleology accounts for the triumph of epigenesis (34). Teleology is a means of explaining phenomena by effects (their purpose or end goal) rather than by causes (how they got there). So influential was teleology on embryology that, by 1810, Lorenz Oken needed no justification for epigenesis beyond this epigram: "The theory of preformation contracts the laws of nature's development" (qtd. in Gould 34-35). In the early nineteenth century, most other scientists followed suit: they stopped asking about the force driving development and instead posed larger questions about the relationship among species and between existing species and their ancestors.

The Victorian Period: Embryology and Evolution

While eighteenth-century embryology centered on whether the embryo is always fully formed or whether it develops part by part over time, nineteenth-century embryologists debated the relationship between individual (ontogeny) and species development (phylogeny). The question of such a relationship arose because scientists noticed similarities between the embryos of one species and another. In Figure 2, Ernst von Haeckel shows the similarity among embryos of pigs (schwein), cows (rind), rabbits (kaninchen), and humans (mensch). Row one depicts all four animals as virtually identical at an early gestational stage. As they gestate, the differences increase, but they remain similar through much of the process. Because of these similarities, scientists began asking: What can we learn about our ancestors by studying the fetal formation and development of an individual organism? Do fetuses provide clues about characteristics our ancestors had and what has changed over time? What, if anything, is the relationship between the development of one species and another? Just as Aristotle had hierarchies, so too did modern scientists. They organized species by "lower order" (less complex in form) and "higher order" (increasingly complex in form), which helped create a framework for such questions.

fetal similarities of various species, including humans

Image of fetal similarities of various species, including humans, from Haeckel's Anthropogenie, oder, Entwickelungsgeschichte des Menschen ... Keimes- und Stammes-geschichte... (1874), from the Wellcome Collection.

In its attempt to answer two major questions, Victorian embryology morphed into evolutionary theory. First, scientists sought to explain why the embryos of existing species resemble those of other existing species (as shown on the right); these explanations allowed them to articulate some basic premises about how development occurs over time. Secondly, Victorian scientists speculated that the embryonic development of existing species provides clues about what their biological ancestors looked like.The idea that ontogeny repeats phylogeny is known as the theory of recapitulation. Most famously promoted by Ernst Haeckel, recapitulation suggests the embryos of higher-order beings such as humans resemble adult forms of lower-order beings such as fish, suggesting that humans evolved from fish. Karl von Baer (1792-1896) and Darwin suggested instead that embryos of existing species resemble those of their ancestors as well as the embryos of other groups of organisms, thus indicating several common ancestors. The most famous example is gill pouches in fish. Whereas Haeckel would argue that gill pouches in human embryos recapitulate the adult forms of gill pouches in ancestral fish, von Baer and Darwin would say that gill pouches in human embryos mirror a similar stage in the development of species more generally (Gould 7). In other words, Haeckel would say humans evolved from fish, but von Baer and Darwin would say humans show similar patterns of development to those of other species, indicating that different species share common ancestors.

Karl Ernst Von Baer's Four Laws of Embryology

In the late 1820s, Von Baer repudiated preformationism by developing the four laws of embryology (Barnes, "Karl Ernst von Baer"):

1. General characteristics of an organism appear in embryo earlier than specialized traits.

2. Organisms become increasingly specialized until the most unique traits emerge.

3. Embryos do not pass through earlier forms; they separate from other forms.

4. Only the embryos of different forms resemble one another; the more complex forms do not repeat the adult stages of less complex forms.

As Barnes explains, the first two laws established that development proceeds epigenetically. The second two laws refuted recapitulation theories such as Haeckel's in rejecting the idea that the embryo of a complex organism is a window into the adult forms of extinct, less complex species (Barnes, "Karl Ernst von Baer").

Ernst Haeckel's Biogenetic Law

In the mid-1860s, influenced by Darwin's On the Origin of Species (1859), German zoologist Ernst Haeckel (1834-1919) formulated the biogenetic law, one of many recapitulation theories. This law asserts a congruence between the stages of animals' embryonic development and their ancestors' adult forms. Studying the embryonic development of living species will therefore provide evidence of past forms' evolutionary development. This theory is typically referred to as ontogeny recapitulates phylogeny. Later embryologists and biologists rejected Haeckel's theories because they could not reproduce his results and suggested that he exaggerated the similarities among different species' or groups' embryos (Barnes, "Ernst Haeckel").

Darwin: Descent with Modification

Darwin's Origin is the most influential scientific text of the Victorian period. In Chapter 13 of Origin, Darwin lays down basic principles of embryology and its relationship to species' development. Assuming that ontogeny maps onto evolutionary relationships, Darwin speculated that humans and other species emerged in branching patterns from several ancestral sources. Shown below is a drawing from Origin in which Darwin attempted to map how species developed from a particular ancestor (and thus account for the similar structures of embryos of animals of different species). The bottom of the illustration shows ancestral forms A, B, C, and so on. Branching off from each are evolutionary changes at different points of development. At the top of the form, we see that a14, q14, and p14 all emerged from a similar branch of A (a "common parent" as Darwin called them) whereas b14 and f14, while traced back to A, deviated into the "f" branch at some point in the evolutionary process.

multi-level 'tree' demonstrating descent with modification

Multi-level "tree" demonstrating descent with modification, from The origin of species by means of natural selection, or The preservation of favoured races in the struggle for life, by Charles Darwin (1872), Wellcome Collection.

Darwin begins Origin with "An Historical Sketch" that references earlier theories: "Until recently the great majority of naturalists believed that species were immutable productions, and had been separately created....Some few naturalists, on the other hand, have believed that species undergo modification, and that the existing forms of life are the descendants by true generation of pre-existing forms." Chapter 13 of Origin provides the most succinct descriptions of his key points and highlights its central concepts: "It has already been casually remarked that certain organs in the individual, which when mature become widely different and serve for different purposes, are in the embryo exactly alike. The embryos, also, of distinct animals within the same class are often strikingly similar."

Here, Darwin concurs with others that embryos begin with general characteristics but become increasingly particular and distinct with growth and development. (Note its similarity to the first of Von Baer's laws of embryology.) As the embryo develops, its form becomes increasingly complex, which is essentially the second of von Baer's laws: "The embryo in the course of development generally rises in organisation" (Darwin). In the following passage, Darwin articulates the first two of von Baer's laws but also reminds readers of von Baer's fourth law that embryos of different species often resemble one another:

How, then, can we explain these several facts in embryology, - namely the very general, but not universal difference in structure between the embryo and the adult; of parts in the same individual embryo, which ultimately become very unlike and serve for diverse purposes, being at this early period of growth alike; - of embryos of different species within the same class, generally, but not universally, resembling each other; - of the structure of the embryo not being closely related to is conditions of existence, except when the embryo becomes at any period of life active and has to provide for itself; - of the embryo apparently having sometimes a higher organisation than the mature animal, into which it is developed. I believe that all these facts can be explained as follows, on the view of descent with modification.

Darwin accepts these laws as facts but explains them in terms of "descent with modification" (i.e., evolution and natural selection).

Darwin theorizes that humans and animals share a common ancestor: "In two groups of animal [sic], however much they may at present differ from each other in structure and habits, if they pass through the same or similar embryonic stages, we may feel assured that they have both descended from the same or nearly similar parents, and are therefore in that degree closely related. Thus, community in embryonic structure reveals community of descent" (Darwin). The "embryonic state" of each group "partially shows us the structure of their less modified ancient progenitors" (Darwin). He concludes that "the innumerable species, genera, and families of organic beings, with which this world is peopled, have all descended, each within its own class or group, from common parents" (Darwin). And here the concept of evolution as we know it today is born. "Descent with modification" is the process by which the species differentiates from its common ancestor, and the embryos of extant species provide a window into the features of those ancient forms.

Unlike preformationists who were adamant about keeping God in the process and epigenesists who had to tiptoe around the question, Darwin rejects the idea of divine will, stirring controversy. Darwin makes it clear that the facts of embryology as enumerated are "inexplicable" by the "ordinary view of creation," that of the Creator's will. Only the theory of descent and modification can explain them.


By the early nineteenth century, the conflict between preformation and epigenesis had concluded in favor of epigenesis and a focus on development rather than first causes, whether labeled God, an "internal mould," "penetrating powers," or a "formative drive." While preformationists were adamant about keeping God in the process, Victorian scientists saw no such need. Such scientists exchanged the question of when and how life begins for questions about the relationship between individual development and humans' ancestral history. By the middle of the nineteenth century, scientists were articulating evolutionary theories that directly challenged preconceived ideas about the universe. Darwin rejected the usual explanations regarding the history of human and animal development and focused instead on what extant species could tell us about our ancestors, creating a system that articulated the evolution of a variety of species from a set of biological ancestors. Blumenbach's "qualitas occulta" gave way to Darwin's evolutionary theories, which set the stage for what we now call "evolutionary development" or "evo-devo" (Hall, "Evolutionary").


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Created 30 March 2023