History
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Three different approaches have been established to study embryos; anatomical, experimental and genetic. Anatomical embryology is the foundation of developmental biology. It addresses the early questions of embryology through studying and comparison of organism development - a field now called comparative embryology - and by looking at how changes in development cause evolutionary change. Anatomical embryology was the first and most simple tool available to early scientists - simple observation which didn’t require technical skill or equipment. Experiments were also used, and advanced as technology created new opportunities and avenues to be discovered. Naturally genetic techniques as we consider them now were not possible until recently, however the study of abnormal embryos was a very useful tool and still is today, as seeing what goes wrong gives an insight into developmental processes.
The field of developmental biology has been studied as early back as 350 B.C, and Aristotle is probably the best known early contributor. Although most people know him best for his philosophy, Aristotle worked extensively with chick eggs and is considered one of the greek fathers of modern biology. He noted the different ways in which animals were born, and defined the two major cell division patterns; holoblastic and meroblastic cleavage patterns.
William Harvey, 1651, concluded all animals, including mammals, developed originally from eggs. Harvey was the first to see the blastoderm of a chick embryo, and the “islands” of blood that develop before the heart. He also suggested that amniotic fluid served as a shock absorber for the embryo. The invention of the microscope in 1600 was a major breakthrough, allowing embryology studies to take a great leap forward by permitting scientists to study embryos in greater detail. In 1672, Marcello Malpighi, defined the neural groove, the muscle-forming somites and the first circulation of the arteries and veins in the chick embryo.
Christian Pander, Karl Ernst von Baer and Heinrich Rathke established embryology into a specific branch of science. Pander and von Baer discovered the three germ layers in 1826 through studies of the chick embryo. Rathke studied the development of frogs, salamanders, fish, turtles, birds and mammals for 40 years, through which he described the formation of the vertebrae skull, the reproductive, respiratory and excretory systems. Karl Ernst von Baer on the other hand revolutionized the study of developmental biology through his four generalizations, which are referred to as the “von Baer laws”. Karl Ernst von Baer also extended on Pander's studies and discovered the notochord, which is the most important aspect in the development of the neural tube.