Ancient Egypt Knowledge of the
placenta goes back at least to ancient Egypt, where it was viewed as the seat of the soul. There was an Egyptian official with the title
Opener of the Kings Placenta. An Egyptian text from the time of
Akhenaten said that a human originates from the egg that grows in women.
Ancient Asia Various interpretations of embryology have existed in Asia throughout history. Included in the ancient Indian tradition of
Ayurveda is
garbhasharir or the study of embryology, which refers to conceptions of embryology from antiquity. Descriptions of the
amniotic sac appear in the
Bhagavad Gita, Bhagavata Purana, and the
Sushruta Samhita. One of the
Upanishads known as the
Garbhopanisaḍ states that the embryo is "like water in the first night, in seven nights it is like a bubble, at the end of half a month it becomes a ball. At the end of a month it is hardened, in two months the head is formed". In Indian literature, the start of consciousness in an embryo is not clearly defined. Some scriptures state that it is active at conception, while others suggest that consciousness begins in the seventh to ninth month of fetal development. Many South Asian traditions, including some Tibetan traditions, believe that the fetus has conscious experiences towards the end of its development. The development of the human embryo is mentioned in the ancient
Buddhist text of (1st–4th century CE). It mentions the human gestation period of 38 days. The text describes embryonic development in first three weeks as a liquid part of yogurt and the differentiation of body parts such as arms, leg, feet and head in the third month. Discussion on various views regarding how long it takes for specific parts of the embryo to form appear in an anonymous document known as the
Nutriment. Ancient Greeks discussed whether only the male had a seed which developed into the embryo within the female womb, or both the male and the female each had a seed that made a contribution to the developing embryo. The difficulty that one-seed theorists confronted was to explain the maternal resemblance of the progeny. One issue that two-seed theorists confronted was why the female seed was needed if the male already had a seed. One common solution to this problem was to assert that the female seed was either inferior or inactive. Another question was the origin of the seed. The encephalomyelogenic theory stated that the seed originated from the brain or and/or bone marrow. Later came pangenesis, which asserted the seed was drawn from the whole body in order to explain the general resemblance in the body of the offspring. Later on, hematogenous theory developed, which asserted that the seed was drawn from the blood. A third question was how or in what form the progeny existed in the seed prior to developing into an embryo and a fetus. According to preformationists, the body of the progeny already existed in a pre-existing but undeveloped form in the seed. Three variants of preformationism were homoiomerous preformationism, anhomoiomerous preformationism, and homuncular preformationism. According to the first, the homoiomerous parts of the body (e.g.
humors, bone) already exist pre-formed in the seed. The second held that it was the anhomoiomerous parts that were pre-formed. Finally, the third view held that the whole was already a unified organic thing. Preformationism was not the only view. According to epigenesists, parts of the embryo successively form after conception takes place.
Hippocrates Some of the most well-known early ideas on embryology come from
Hippocrates and the
Hippocratic Corpus, where discussion on the embryo is usually given in the context of discussing
obstetrics (pregnancy and childbirth). Some of the most relevant Hippocratic texts on embryology include the
Regimen on Acute Diseases,
On Semen, and
On the Development of the Child. Hippocrates claimed that the development of the embryo is put into motion by fire and that nourishment comes from food and breath introduced into the mother. An outer layer of the embryo solidifies, and the fire within consumes humidity which makes way for development of bone and nerve. The fire in the innermost part becomes the belly and air channels are developed in order to route nourishment to it. The enclosed fire also helps form veins and allows for circulation. In this description, Hippocrates aims at describing the causes of development rather than describing what develops. Hippocrates also develops views similar to
preformationism, where he claims that all parts of the embryo simultaneously develop. Hippocrates also believed that maternal blood nourishes the embryo. This blood flows and coagulates to help form the flesh of the fetus. This idea was derived from the observation that menstrual blood ceases during pregnancy, which Hippocrates took to imply that it was being redirected to fetal development. Hippocrates also claimed that the flesh differentiates into different organs of the body, and Hippocrates saw as analogous an experiment where a mixture of substances placed into water will differentiate into different layers. Comparing the seed to the embryo, Hippocrates further compared the stalk to the umbilical cord.
Aristotle Some embryological discussion appears in the writings of Aristotle's predecessor
Plato, especially in his
Timaeus. One of his views were that the bone marrow acted as the seedbed, and that the soul itself was the seed out of which the embryo developed, though he did not explain how this development proceeded. Scholars also continue to debate the views he held on various other aspects of embryology. Some ideas related to embryology also appear in his
History of Animals,
On the Parts of Animals,
On Respiration, and
On the Motion of Animals. Means by which we know Aristotle studied embryology, and most likely his predecessors as well, was through studying developing embryos taken out from animals as well as aborted and miscarried human embryos. Aristotle believed that the female supplied the matter for the development of the embryo formed from the menstrual blood, whereas the semen that comes from the male shapes that matter. Aristotle's belief that both the male and female made a contribution to the actual fetus goes against some prior beliefs. According to
Aeschylus and some Egyptian traditions, the fetus solely develops from the male contribution and that the female womb simply nourishes this growing fetus. On the other hand, the
Melanesians held that the fetus is solely a product of the female contribution. Aristotle did not believe there were any external influences on the development of the embryo. Against Hippocrates, Aristotle believed that new parts of the body developed over time rather than all forming immediately and developing from then on. He also considered whether each new part derives from a previously formed part or develops independently of any previously formed part. On the basis that different parts of the body do not resemble each other, he decided in favor of the latter view. He also described development of fetal parts in terms of mechanical and automatic processes. In terms of the development of the embryo, he says it begins in a liquid-like state as the material secreted by the female combines with the semen of the male, and then the surface begins to solidify as it interacts with processes of heating and cooling. The first part of the body to differentiate is the heart, which Aristotle and many of his contemporaries believed was the location of reason and thinking. Aristotle claimed that vessels join to the uterus in order to supply nourishment to the developing fetus. Some of the most solid parts of the fetus cool and, as they lose moisture to heat, turn into nails, horns, hoofs, beaks, etc. Internal heat dries away moisture and forms sinews and bones and the skin results from drying of the flesh. Aristotle also describes the development of birds in eggs at length. He further described embryonic development in dolphins, some sharks, and many other animals. Aristotle singularly wrote more on embryology than any other pre-modern author, and his influence on the subsequent discussion on the subject for many centuries was immense, introducing into the subject forms of classification, a comparative method from various animals, discussion of the development of sexual characteristics, compared the development of the embryo to mechanistic processes, and so forth.
Later Greek embryology Reportedly, some
Stoics claimed that most parts of the body formed at once during embryological development. Some
Epicureans claimed that the fetus is nourished by either the amniotic fluid or the blood, and that both male and female supply material to the development of the fetus. According to the writings of
Tertullian,
Herophilus in the 5th century BC described the ovaries and fallopian tubes (but not past what was already described by Aristotle) and also dissected some embryos. One advance Herophilus made, against the conceptions of other individuals such as Aristotle, was that the brain was the center of intellect rather than the heart. Though not a part of Greek tradition, in
Job 10, the formation of the embryo is likened to the curdling of milk into cheese, as described by Aristotle. Whereas Needham sees this statement in Job as part of the Aristotelian tradition, others see it as evidence that the milk analogy predates the Aristotelian Greek tradition and originates in Jewish circles. In addition, the
Wisdom of Solomon (7:2) also has the embryo formed from menstrual blood.
Soranus of Ephesus also wrote texts on embryology which went into use for a long time. Some rabbinic texts discuss the embryology of a female Greek writer named Cleopatra, a contemporary of
Galen and Soranus, who was said to have claimed that the male fetus is complete in 41 days whereas the female fetus is complete in 81 days. Various other texts of less importance also appear and describe various aspects of embryology, though without making much progress from Aristotle.
Plutarch has a chapter in one of his works titled "Whether was before, the hen or egg?" Discussion on embryological tradition also appears in many
Neoplatonic traditions. Next to Aristotle, the most impactful and important Greek writer on biology was
Galen of Pergamum, and his works were transmitted throughout the
Middle Ages. Galen discusses his understanding of embryology in two of his texts, those being his
On the Natural Faculties and his
On the Formation of the Foetus. There is an additional text spuriously attributed to Galen known as
On the Question of whether the Embryo is an Animal. Galen described embryological development in four stages. In the first stage, the semen predominates. In the second stage, the embryo is filled with blood. In the third stage, the main outlines of the organs have developed but various other parts remain undeveloped. In the fourth stage, formation is complete and has reached a stage where we can call it a child. Galen described processes that played a role in furthering development of the embryo such as warming, drying, cooling, and combinations thereof. As this development plays out, the form of life of the embryo also moves from that like a plant to that of an animal (where the analogy between the root and umbilical cord is made). Galen claimed that the embryo forms from menstrual blood, by which his experimental analogy was that when you cut the vein of an animal and allow blood to flow out and into some mildly heated water, a sort of coagulation can be observed. He gave detailed descriptions of the position of the umbilical cord relative to other veins.
Patristics The question of embryology is discussed among a number of
early Christian writers, largely in terms of theological questions such as whether the fetus has value and/or when it begins to have value. (Although a number of Christian authors continued the classical discussions on the description of the development of the embryo, such as
Jacob of Serugh. Passing reference to the embryo also appears in the eighth hymn of
Ephrem the Syrian's
Paradise Hymns.) Many
patristic treatments of embryology continued in the stream of Greek tradition. The earlier Greek and Roman view that it was not was reversed and all pre-natal infanticide was condemned.
Tertullian held that the soul was present from the moment of conception. The
Quinisext Council concluded that "we pay no attention to the subtle division as to whether the foetus is formed or unformed". In this time, then, the Roman practice of child exposure came to an end, where unwanted yet birthed children, usually females, were discarded by the parents to die. Other more liberal traditions followed
Augustine, who instead viewed that the animation of life began on the 40th day in males and the 80th day in females but not prior. Before the 40th day for men and 80th day for women, the embryo was referred to as the , and after this period was reached, it was referred to as the . The notion originating from the Greeks that the male embryo developed faster remained in various authors until it was experimentally disproven by
Andreas Ottomar Goelicke in 1723. Various patristic literature from backgrounds ranging from
Nestorian,
Miaphysite and
Chalcedonian discuss and choose between three different conceptions on the relation between the soul and the embryo. According to one view, the soul pre-exists and enters the embryo at the moment of conception (). According to a second view, the soul enters into existence at the moment of conception (). In a third view, the soul enters into the body after it has been formed (). The first option was proposed by
Origen, but was increasingly rejected after the fourth century. On the other hand, the other two options were equally accepted after this point. The second position appears to have been proposed as a response to Origen's notion of a pre-existing soul. After the sixth century, the second position was also increasingly seen as Origenist and so rejected on those grounds. The writings of Origen were condemned during the Second
Origenist Crises in 553. Those defending usually appealed to the Platonic notion of an eternally moving soul. Those defending the second position also appealed to Plato but rejected his notion on the eternality of the soul. Finally, those appealing to the third position appealed both to Aristotle and scripture. Aristotelian notions included the progression of the development of the soul, from an initial plant-like soul, to a sensitive soul found in animals and allows for movement and perception, and finally the formation of a rational soul which can only be found in the fully-formed human. Furthermore, some scriptural texts were seen as implying the formation of the soul temporally after the formation of the body (namely Genesis 2:7; Exodus 21:22–23; Zachariah 12:1). In the
De hominis opificio of
Gregory of Nyssa, Aristotle's triparitate notion of the soul was accepted. Gregory also held that the rational soul was present at conception.
Theodoret argued based on Genesis 2:7 and Exodus 21:22 that the embryo is only ensouled after the body is fully formed. Based on Exodus 21:22 and Zachariah 12:1,
Philoxenus of Mabbug claimed that the soul was created in the body forty days after conception. In his
De opificio mundi, the Christian philosopher
John Philoponus claimed that the soul is formed after the body. Later still, the author
Leontius held that the body and soul were created simultaneously, though it is also possible he held that the soul pre-existed the body. Some Miaphysites and Chalcedonians seemed to have been compelled into accepting in the case of Jesus because of their view that the incarnation of Christ resulted in both one hypostasis and one nature, whereas some Nestorians claimed that Christ, like us, must have had his soul formed after the formation of his body because, per Hebrews 4:15, Christ was like us in all ways but sin. (On the other hand, Leontinus dismissed the relevance of Hebrews 4:15 on the basis that Christ differed from us not only in sinfulness but also conception without semen, making another of Christ's supernatural feats.) They felt comfortable holding this view, under their belief that the human nature of Jesus was separate from the divine
hypostasis. Some Nestorians still wondered, however, if the body united with the soul in the moment the soul was created or whether it came with it only later. The Syriac author
Babai argued for the former on the basis that the latter was hardly better than
adoptionism.
Maximus the Confessor ridiculed the Aristotelian notion of the development of the soul on the basis that it would make humans parents of both plants and animals. He held to
synhyparxis and regarded the other two positions both as incorrect extremes. After the 7th century, Chalcedonian discussion on embryology is slight and the few works that touch on the topic support
synhyparxis. But debate among other groups remains lively, still divided on similar sectarian grounds. The patriarch
Timothy I argued that the
Word first united with the body, and only later with the soul. He cited John 1:1, claiming on its basis that the Word became flesh first, not a human being first. Then,
Jacob of Edessa rejected
prohyparxis because Origen had defended it and
methyparxis because he believed that it made the soul ontologically inferior and as only being made for the body. Then,
Moses Bar Kepha claimed, for Christological reasons as a Miaphysite, that only
synhyparxis was acceptable. He claimed that Genesis 2:7 has no temporal sequence and that Exodus 21:22 regards the formation of the body and not the soul and so is not relevant. To argue against
methyparxis, he reasoned that body and soul are both present at death and, because what is at the end must correspond to what is also at the beginning, conception must also have body and soul together. == Embryology in Religious Context ==