Historical Gleanings
If I have seen further, it is by standing on the shoulders of giants. —Sir Isaac Newton, English mathematician, 1643–1727
This statement, made more than 300 years ago, emphasizes that each new study of a problem rests on a base of knowledge established by earlier investigators. The theories of every age offer explanations based on the knowledge and experience of investigators of the period. Although we should not consider them final, we should appreciate rather than scorn their ideas. People have always been interested in knowing how they developed and were born and why some embryos and fetuses develop abnormally. Ancient people developed many answers to the reasons for these birth defects.
Ancient Views of Human Embryology
Egyptians of the Old Kingdom, approximately 3000 BC, knew of methods for incubating birds’ eggs. Akhnaton (Amenophis IV) praised the sun god Aton as the creator of the germ in a woman, maker of the seed in man, and giver of life to the son in the body of his mother. The ancient Egyptians believed that the soul entered the infant at birth through the placenta.
A brief Sanskrit treatise on ancient Indian embryology is thought to have been written in 1416 BC. This scripture of the Hindus, called Garbha Upanishad , describes ancient views concerning the embryo. It states:
From the conjugation of blood and semen [seed], the embryo comes into existence. During the period favorable for conception, after the sexual intercourse, [it] becomes a Kalada [one-day-old embryo]. After remaining seven nights, it becomes a vesicle. After a fortnight it becomes a spherical mass. After a month it becomes a firm mass. After two months the head is formed. After three months the limb regions appear.
Greek scholars made many important contributions to the science of embryology. The first recorded embryologic studies are in the books of Hippocrates of Cos , the famous Greek physician (circa 460–377 BC), who is regarded as the father of medicine . To understand how the human embryo develops, he recommended:
Take twenty or more eggs and let them be incubated by two or more hens. Then each day from the second to that of hatching, remove an egg, break it, and examine it. You will find exactly as I say, for the nature of the bird can be likened to that of man.
Aristotle of Stagira (circa 384–322 BC), a Greek philosopher and scientist, wrote a treatise on embryology in which he described the development of the chick and other embryos. Aristotle promoted the idea that the embryo developed from a formless mass, which he described as a “less fully concocted seed with a nutritive soul and all bodily parts.” This embryo, he thought, arose from menstrual blood after activation by male semen.
Claudius Galen (circa 130–201 AD), a Greek physician and medical scientist in Rome, wrote a book, On the Formation of the Foetus , in which he described the development and nutrition of fetuses and the structures that we now call the allantois, amnion, and placenta.
The Talmud contains references to the formation of the embryo. The Jewish physician Samuel-el-Yehudi, who lived during the second century AD, described six stages in the formation of the embryo, from a “formless, rolled-up thing” to a “child whose months have been completed.” Talmud scholars believed that the bones and tendons, the nails, the marrow in the head, and the white of the eyes were derived from the father, “who sows the white,” but the skin, flesh, blood, and hair were derived from the mother, “who sows the red.” These views were according to the teachings of both Aristotle and Galen.
Embryology in the Middle Ages
The growth of science was slow during the medieval period, but a few high points of embryologic investigation undertaken during this time are known to us. It is cited in the Quran (seventh century AD), the holy book of Islam, that human beings are produced from a mixture of secretions from the male and female. Several references are made to the creation of a human being from a nutfa (“small drop”). Reference is made to the leech-like appearance of the early embryo. Later the embryo is said to resemble a “chewed substance.”
Constantinus Africanus of Salerno (circa 1020–1087 AD) wrote a concise treatise entitled De Humana Natura . Africanus described the composition and sequential development of the embryo in relation to the planets and each month during pregnancy, a concept unknown in antiquity. Medieval scholars hardly deviated from the theory of Aristotle , which stated that the embryo was derived from menstrual blood and semen. Because of a lack of knowledge, drawings of the fetus in the uterus often showed a fully developed infant frolicking in the womb ( Fig. 1.2 ).
A–G , Illustrations from Jacob Rueff’s De Conceptu et Generatione Hominis (1554) showing the fetus developing from a coagulum of blood and semen in the uterus. This theory was based on the teachings of Aristotle, and it survived until the late 18th century.
