Luc Brisson—The Philosophical History of the Human Embryo

Luc Brisson—The Philosophical History of the Human Embryo



BrissonThe following paper was presented by Luc Brisson, Research Director at France’s National Centre for Scientific Research (CNRS) at “Defining Platonism: A Conference in Honor of John Dillon’s 75th Birthday.” The event, which took place on September 13-14, 2014, in Berkeley, California, was co-hosted by Franciscan University of Steubenville’s Classics Department, the University of Iowa’s Classics Department, and University of California Berkeley’s Department of Philosophy.

The embryo

Pre-natal life can be understood in two ways. It can designate life before conception, and life as comprised between the moment of conception and the moment of birth, that is, the life of the embryo. I am going to concentrate on this second meaning, although, at least as far as Plato and the Platonists are concerned, I will have to take the second meaning into account. In this context, I will try to reflect on the various viewpoints – medical, philosophical and theological – which, from the 5th century B.C. to the 18th century, have tried to answer the question: when does one become a human being? I will do so by reflecting respectively on conception, gestation, and birth.


In the background of all philosophical and theological debates, we find the works of two doctors, Hippocrates (5th century B.C.) and Galen (2nd century A.D.).

1.Conception. For Hippocrates and Galen, whose positions will tend to merge in the medical texts of the end of Antiquity, the embryo results from a mixture of the male’s sperm with that of the female, for according to them both male and female produce sperm. It is the predominance of one over the other that accounts for the sex of the child to be born. Thus, the two seeds combine as a result of the female’s movements, then the mixture is heated as an effect of internal heat. It is this heating that provokes its coagulation, like a porridge that “takes” when one heats the mixture of milk and flour.

2. Gestation. Between conception and birth, a crucial stage is that of formation, that is, the moment when the embryo acquires a human form. Many philosophers or theologians situate the acquisition of the animal, or even rational soul at this stage, which is not the case in Hippocrates or in Galen, who do not take the soul into account. Complex calculations lead to a specific set of numbers, more or less symbolic, with the fortieth day being preferred. In both cases, one opts for a gradual development of the embryo, which goes through conception, pregnancy, and birth.

3.Birth. On the threshold of the eighth month, the child descends into the womb to prepare its departure. The process of childbirth is described at the end of the Hippocratic treatise On the nature of the child: it is the movements of the child, who feels cramped in a womb that has become too small, that triggers this process of birth by breaking the membranes. As soon as one is broken, the others are rendered fragile and break in their turn.



In Plato’s Timaeus, the sperm, which comes from the marrow, transports living beings that are so small as to be invisible, and are still formless. These living beings are sowed in the womb, as in ploughed land, where they will grow and differentiate, and whence they will emerge into the light upon birth (Timaeus 91c-d). Yet things are not as simple as they appear. One must take account, first and foremost, of the life of the soul, for the soul lives before all incarnations, and it survives the destruction of the body, which it inhabits temporarily.

The central myth of the Phaedrus (245c-249d) describes it accompanying the gods and demons who leave the sphere of the world to go contemplate the intelligible. It is the quality of their contemplation that will justify their first incarnation in a specific body. Once it falls into a body, the soul forgets its past visions, and it is the process of reminiscence that will enable it to rediscover them. And since the soul survives the dissolution of the body, which it inhabits temporarily, it is the quality of its previous life which explains that at each new incarnation, it enters such-and-such a new body, as is described in the Phaedrus (249d-252c) and especially in the Timaeus (90e-92c). A human soul can pass from the body of a man to that of a woman, to that of a bird, a quadruped, a reptile or a fish, with the oyster occupying the lowest position. In short, the soul is alive before any incarnation, but Plato proposes no explanation to account for its entry into one body or another. One will have to wait half a millennium, for Plotinus and Porphyry, for the question to be raised in this context.


In Aristotle (4th century B.C.), the development of the embryo is also gradual.

1. Conception. There is a single seed, that of the male, which provides the form and finds in the uterus a nest it which it can develop, whereas the female provides the matter. Matter, through its resistance, is therefore the cause of all monstrosity.

2. Formation. Aristotle maintains a progressive development by the successive formation of parts in accordance with the final orientation defined by the form, or the soul, which also goes through a vegetative, then an animal stage. The first organ to be formed in the embryo is the heart or its equivalent, that is, the principle of life, motion, and sensitivity. Nevertheless, the embryo is imperfect or incomplete, since it receives its nourishment from someone else by means of the umbilical cord. One must therefore reconcile, on the one hand, the fact that the embryo is dependent, imperfect being, and, on the other, the belief that once it is formed, it possesses within itself a proper principle of development, viz. the heart. The solution consists in saying that this principle is not absolutely primary, for it is secondary with regard to the only principle that can be absolutely first within the animal, i.e. the soul.

3 Birth. Thus, the embryo is not yet an animal in act, in the strict sense, but it is already an animal potentially, and it does not become an animal in act until birth. In short, in his research on the embryo, Aristotle mobilizes the theoretical instruments of form and matter, potency and act.

The Stoics

The Stoics consider the universe as a divine, living unity, organized according to rational laws and governed in its slightest details by Providence. At the basis of their cosmology, they place the following two principles. One has only the ability to undergo action: it is matter (húle), bereft of all determination, all motion and all initiative. The other, lógos , has the ability to act, and brings form, quality, and motion to matter. By taking the demand for matter’s indeterminacy to an extreme, Stoicism finds itself forced to acknowledge the lógos alone as the cause of the most elementary physical characteristics, those of the four elements (fire, air, water, earth) and those of the result of the combination of these four elements in sensible things. This is why one may speak of Stoic “corporealism”: the action of the lógos on matter and on bodies remains an activity, which is corporeal.

This fire that is the lógos identified as a god can also be conceived as an igneous breath, the omnipresent pneûma. In all the parts of the world penetrated by this pneûma and informed by it, fire, which is hot, is associated with expansion, while air, which is cold, is characterized by contraction. This oscillation, which animates all bodies and ensures their cohesion, is called “tension” (tónos), a tension that is diversified according to the regions of the universe: it assumes the name of “constitution”, “tenor” or “maintenance” (héxis) in inanimate solids, of “growth” (phúsis) in plants, and of “soul” (psukhé) in animals. In any case, however, its function is to unify all bodies, including and especially the body of the universe.

1.Conception. It is the father’s sperm that transports the formative reasons (lógoi), which derive from the lógos, into the womb.

2.Formation. For the Stoics, the embryo is simply a part of the woman’s womb, which features all the characteristics of a plant. Its breath (pneuma) is that of a plant, it breathes and feeds itself like a plant, for it is bereft of the sensations, impulses and spontaneous movements that are proper to animals; it is endowed only with the functions of nutrition and growth. The soul really appears only at birth, when the vegetable breath is transformed into animal breath as an effect of cold air, in a phenomenon similar to the tempering of melted metal plunged into cold water. Despite this image, the Stoics did not represent the embryo simply as a vegetable: as the moment of birth approaches, the embryo’s vegetable breath becomes progressively finer, to become animal breath.

3. Birth. If the embryo is not an animal, but a vegetable, it is modified progressively, until it leaves behind its vegetable status at birth. Although it is sudden, this change in the nature of the embryo, which moves from vegetable to animal, is thus merely the last stage of a progressive transformation. It can therefore exhibit the sensations, impulses, and spontaneous motions that are proper to the animal. The embryo is therefore “like a plant” or similar to a plant, more than it is a plant in the strict sense.

Plotinus and Porphyry

Plotinus and Porphyry seem to have adopted a similar position as far as the question of the embryo is concerned, both of them attempting a synthesis between Platonism and Stoicism.

1. Conception. It is the father’s sperm that transports into the mother’s womb the formative reasons (lógoi) concealed by nature, that is, the lower or vegetative part of the world soul. Conception, which enables the production of an embryo, first takes place by means of sperm, which is a piece of matter animated by a vegetative soul, and administered by the father’s higher soul. When this sperm is in the womb, it is the mother’s higher soul that administers it. In fact, what the seed conveys are “reasons” (lógoi) that will serve to produce an embryo.

2 Formation. The treatise entitled On the way in which the embryo receives the soul, dedicated “To Gauros” (= Pròs Gaûron, in Greek, and Ad Gaurum, in Latin), was first attributed to Galen, but now is ascribed to Porphyry. It essentially takes up the Stoic position, which it radicalizes in a Platonic context, as was the case for Plotinus.

Following Plotinus, Porphyry distinguishes between the divine, total soul, that is the hypostasis Soul, which always remains within the Intelligible, and particular souls. The divine or total Soul is what is traditionally called the hypostasis Soul. To this soul, which is and remains unique, are attached all the other souls, both the world soul and the human souls. All these souls remain united and form one single soul, before they are projected here and there like light which, when it reaches the earth, is distributed without being divided. The world soul produces and administers bodies. In order to understand the process in its entirety, we must remind ourselves, in general terms, of the constitution of the universe. The hypostasis Soul receives within itself the intelligible forms in the mode of “reasons”. The lowest part of the world soul, its vegetative power, or Nature, implants these “reasons” within matter. Thus there appears body, which can be described as a set of qualities that come to attach themselves to an ógkos, that is, a piece of matter endowed with size. In short, a body is a composite made of matter with which a specific size endowed with qualities has become associated; ultimately, this size and these qualities are “reasons”, that is, forms that are engaged within matter. Now, a body may or may not be alive. Every living body is animated by a vegetative power, responsible for its nutrition, growth, and reproduction, and this vegetative power comes directly from the world soul. In the case of human beings, the father transmits it through his sperm, which, once it enters the womb, produces an embryo. At birth, a human soul that comes from outside is associated with the vegetative soul that animates the embryo to form a human baby. However, this soul that has descended remains rooted up above through its intellect.

For the author of the Ad Gaurum, the embryo is a vegetable, endowed with merely vegetative power, which ensures its nutrition and growth, and it does not become an animal that can move itself and exhibit sensation, impulse, and representation until after birth, from the moment when it receives from without a soul that is adapted to it. To understand the nature of this aptitude (epitedeiótes), the Aristotelian notion of potency must be enlarged. It is no longer the potency of an oar which remains capable of moving a boat forward even when it has fallen into the sea, but of the potency of a piece of wood appropriate for making an oar, a kind of potency of potency. The embryo is an animal in potency, not because it is already capable of developing the distinctive faculties of an animal within the mother’s womb, but because it is apt since birth to receive an animal soul that was previously elsewhere, separate from it.

3Birth. Yet the problem becomes complicated with the introduction of an ethical criterion, for a soul can enter a body only as a function of the aptitude that body has to receive it, and this aptitude is determined by the quality of that soul’s previous life.


The context changes radically with the great monotheistic religions. The question of the formation and animation of the embryo receives its answer from the outset: God’s intervention, although the balancing point of this answer shifts as a function of the major concerns of the various religious traditions.


For the Jewish world, the answer was found in verse of chapter 2 of Genesis, which is, moreover, cited by Porphyry in his To Gaurus: “And Adonaï Elohim formed man (adam), the dust of humus (adama), and he blew into his nostrils a breath of life (nishmat haïm) and man became a living being (nephesh haya)”. Throughout its history, Rabbinic literature refrains from any philosophical exposition on the subject, and limits itself to constituting a collection of data that shows real medical knowledge, but whose primary function is of another order, essentially prescriptive, especially in the domain of the pure and the impure, that is, in a Jewish context, of the religious. Nevertheless, the embryo seems to be considered a human being after 40 days of gestation.


It was quite naturally to the same verse of Genesis that the Christians referred as far as the formation of the embryo was concerned. For the rest, they adapted the doctrines of the philosophers. Aristotle’s theory remained predominant among the ancient Christians, especially as far as generation is concerned. Only the question of soul’s immediacy in its spiritual reality, closely linked to the question of early abortion, opposed philosophers to the Fathers of the primitive Church.

Theories of the animation of the embryo and its accession to humanity evolved in the western Middle Ages. If the first Scholastics viewed animation as a sudden event, while denying the embryo a proper life prior to this moment, the influence of Aristotle led the Medievals to consider the development of the embryo as a gradual, physiological process, while their positions varied between partisans of the unicity and the plurality of forms, but also within each camp. Nevertheless, a broad consensus existed since the 12th century on one point: the human soul comes from God, and its introduction presupposes a corresponding corporeal and functional organization. From the 13th century, the Scholastics admitted, of course, with Aristotle, that the embryo is animated rather early at the beginning of gestation, but this is not yet the intellective soul. Only a small minority defended the complete animation of the human embryo since conception, in the name of the soul’s unity.

The common opinion does not imply that the child that is to be born is not animated until it becomes viable, that is, according to medieval theories, at seven months of gestation. The introduction of the intellectual soul takes place much earlier, in the first months of pregnancy, at the moment when the embryo acquires the contours of the human form. When the medieval authors suggest precise figures, they vary from thirty to ninety days. Nevertheless, their position differs considerably from the current doctrine of the Catholic Church.

The rejection of immediate animation has philosophical reasons, for this hypothesis leaves scarcely any room for nature: how can the soul be associated with a body that is not yet adapted to it? Yet this rejection can be explained especially because of the sacrament of baptism, the precondition for spiritual salvation. Following Augustine, medieval theologians prohibited unbaptized children, although innocent, from entering paradise. Some practices and beliefs, encouraged or tolerated by the Church, and whose appearance was parallel to the accentuation of the importance of baptism, attenuated the painful implications of the Augustinian doctrine. These include 1) first of all, the practice of summary baptism, 2) then, beginning with the 12th and 13th centuries, the existence of limbo, a place in the beyond without suffering, reserved for those who could not be baptized, either because they were born before Christ or died before having been baptized, et 3) finally, at the beginning of the modern age, those respite sanctuaries where a child was brought to await a miraculous sign that would allow it to be baptized. To situate animation at conception would have led to an absurd increase in the number of damned souls, given the number of miscarriages.

This problem does not arise in the Eastern Church, which makes no room for original sin, and it may be no coincidence if the theory of immediate animation is very widespread there, as an adaptation of the positions on this subject of the Church Fathers Basil of Caesarea, Gregory of Nyssa, and Maximus Confessor.


If we turn to Islam, we note that as far as the origin of the embryo is concerned, the authors of the 9th century followed especially Hippocrates. They later sided with Aristotle. As far as the characters and phases of development of the embryo are concerned, philosophers as well as physicians continued to base themselves on Hippocrates and Galen, showing, moreover, a very widespread interest in astrology. The links between revelation and scientific and philosophical research were always very close in Islam, and embryology was no exception to this rule, which explains why the Koran remains an essential source for Islamic embryology.

The Holy Book of Islam uses embryology primarily to provide proofs of divine omniscience and omnipotence. What is more, the constitution of the embryo is systematically linked to God’s creative action: All the theses concerning the embryo are introduced by the verb “to create”. From a technical viewpoint, the evolution of the embryo goes through three phases. First, the sperm takes its place within a solid receptacle, the uterus, where it is transformed into a clot of blood, then into a piece of chewed-up flesh; finally, the bones are formed and covered with flesh. According to the theologians, each of these three phases lasts forty days. They are followed by a further phase, described in several ways, but generally interpreted as indicating the “humanization” of the embryo, or the insufflation of breath within it. In addition, the Koran establishes a fixed duration for pregnancy which, including the period of nursing, is thirty months.

19th-20th centuries

Leaving to one side the analyses of the formative cause, the 19th century would take up the epigenesis of Caspar Friedrich Wolff on the question of embryonic layers, which it would later reinterpret in the context of cellular theory. It was not until much later, with genetics and molecular biology, that the question of the material conditions of the realization of an organizational plan could really be tackled. This restructuring of biological knowledge, which was to lead to contemporary biomedical knowledge and its increased technical capacities for interventions, while it does indeed constitute a new biological order, has its repercussions. It leaves aside the anthropological status of the embryo, to which the problem of animation was initially attached.

The door was open, and extraordinary scientific and technological advances did not take long to occur. However, on such burning issues as methods of assisted procreation that imply the destruction of a large number of viable embryos, experimentation on embryos in the context of research, cloning, and more generally abortion, science and technology have nothing to say, and must yield to theology and philosophy which, for better or worse, have for millennia molded public opinion and behavior which, in the face of possible change, tend to react with greater or lesser degrees of violence. When does one become a human being? This question, which science and technology cannot answer, cannot be avoided.

Luc Brisson

Translation by Michael Chase