Embryology is the study of the formation of life, part of the studies with which developmental biology is concerned. Developmental biology examines how all forms of life begin, and how they develop into fully formed and functioning organisms. Embryology's focus is much narrower.
An embryologist looks at the beginning of life from the one-celled organism, egg or sperm. Embryologists examine fertilization and track the development of the embryo until it bears a resemblance to its progenitors. For example, in human conception, embryologists would be interested in both sperm and egg, and the meeting of the two, and then would follow egg implantation and the growth of an embryo until it reaches the fetal stage. So in humans, the study of an embryo would last until about the second month of a pregnancy.
Some embryologists further examine the full development of different organs in the body. For example, neuroembryology studies the way the spinal chord and central nervous system develop from the fertilized egg. Cardiologists employ embryology so they can classify the way a fertilized egg develops into the heart and lungs.
Aristotle was one of the first to champion the theory of epigenesis, the concept that life forms develop into complex organisms from fertilization. This was not a popular concept and was largely discarded in favor of the theory of preformation, which suggested that each human sperm was already a person in waiting. In the mid 18th century, Caspar Fredriech Wolff again set forth the concept of epigenesis. Through his study of chick embryos, Wolff realized that the body of an organism has stages of development. Through vivisection, he observed the complexity of specific organs and contended that their development could not simply have occurred spontaneously, but must have developed over time.
Later scientists followed his studies, and with the development and subsequent improvements of the microscope, Wolff's theories were found to be quite accurate. Wolff is credited as the "Father of Embryology," even though he did not first conceptualize epigenesis. Today, the theories of embryology are easier to prove because of the accuracy with which we can examine DNA codes within a cell.
There are several practical applications of embryology in the modern world. Embryology has given doctors the tools to create fertilized eggs for in vitro implantation. Embryology can also identify risk factors for serious genetic conditions within the fertilized egg and select the most viable eggs for implantation. The study of embryology has led directly to the concept of cloning, either for a whole organism or parts of an organism.
Cloning and in vitro fertilization have both been subject to tremendous debate. Part of the problem lies within each embryology textbook. They all state that life begins at the moment of conception. While it is true that some form of life begins at conception, the degree, value and quality of such a life is not addressed. Hence, abortion proponents and opponents have been arguing about this concept before and since the legalization of abortion.
Cloning is even more hotly contested. Some in the field of embryology suggest that life cannot begin in a Petri dish, and therefore any created embryos are not really "alive." Others refute this concept absolutely and believe that the manipulation of human cells is "playing God," and as such is immoral and potentially dangerous. No doubt this debate will continue, particularly in regard to legislation that allows for the extraction of stem cells from human embryos.