Embryology – historical overview and current achievements

Embryology is maybe the first thing that comes to mind when the term “developmental biology” is mentioned. It is, quite self-evidently from the name, the study of the embryo and the prenatal development altogether, but also it focuses on the formation of gametes and the fertilization – two processes without which the embryo doesn’t really come to be (with a few exceptions, of course).

Embryology seems to have been a subject of interest and study for a very long time. In the recorded history the first theory that concerns embryology, and the development of new life in general, belongs to the Greek philosopher Aristotle who lived in 384–322 BC. His idea at the time was that living organisms develop from an egg or a seed via series of consecutive steps that transform the relatively simple seed or egg into a complex organism. While this almost seems like a common sense nowadays, consider that Aristotle’s theory was proposed in a time when humanity knew nothing about cells, cell and tissue differentiation and all the intricate molecular mechanisms that stand behind these processes. One might even say Aristotle’s work is genius and as a testament of that stands the fact that his theory seems to not have been widely understood until much later.

Statue of Aristotle
Bust statue of Aristotle (384–322 BC)

The theory of “Preformationism” was the domination one from seventeenth until the beginning of nineteenth century (roughly timed). This theory suggested that all life was created during the Creation and new generations develop from already existing miniature versions of themselves. As a simple example, the eggs inside a woman’s body contain tiny human beings that eventually start to grow and become babies that are born. This is the so called “ovism model”. Later, when the magnifying lenses were improved and sperm cells were observed, a competing model was suggested, the “spermism model” according to which the tiny human being (also called homunculus) was in the sperm cells. With the perfection of the magnifying lenses and the gathering of more and more data on the cells and their structure, the preformationism theory was eventually abandoned.

Homunculus  inside a sperm
A small human inside a sperm – preformism drawing by Nicolaas Hartsoeker (1695)

Nowadays a central subject of study for the embryology is the development of the embryo, its genetic basis, the intercellular communication involved in the process of forming the proportions, the tissue cells and layers, the timing and positioning and all other mechanisms that allow a complex organism to develop from a single cell. In a way to understand the normal process one can benefit greatly by studying the deviations from it, therefore certain mutations in genes related to the development or other disruptions of the normal process by different internal or external causes, are also of vivid interest in the field of embryology.

The practical applications of the embryological science seem endless. It already allows us to monitor the health and the development of our babies as well of these of our pets, it made possible the so called in-vitro insemination which provides a way for thousands of couples who, for one or another reason, are unable to conceive a child in the usual manner. It is again because of the advances of embryology that treatments of unborn babies with various health issues are now possible.