By Robert Hazen, George Mason University
The history of genetics can be divided into three major eras. First came classical genetics: the study of genetics at the level of organisms and their traits. Then came cellular genetics, when microscopes became good enough that we could actually look inside the cell and see what was happening as cells divided. Finally, molecular genetics: looking at genetics at the scale of the molecule that contains the genetic code, DNA.
Classical Genetics
Let’s begin with classical genetics, which looks at how biological information is passed from parents to offspring at the level of complete organisms—animals and plants, for example. Humans have studied this for thousands of years, because they have taken advantage of a simple fact of life, that “like begets like”. In humans, just as in other animals and in plants, offspring bear a resemblance to their parents.
If you’ve seen a family photo album, you can tell immediately that people are related. Parents and children, cousins, aunts and uncles, and so forth; families have resemblances because of the passing-down of similar traits.
Classic Genetics in Breeding Animals
This phenomenon has been exploited since prehistoric times in the selective breeding of animals—domesticated animals such as sheep and dogs, of course; horses, and all the different varieties of these animals that we use in various ways. Sometimes, breeders took advantage of the “sports of nature”; these were mutants that had particularly unusual qualities.
Dwarf animals, for example, or giants; particularly fertile animals, or particularly productive ones, of one sort or another. People have used these in selective breeding to develop new types, new varieties of organisms.
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Selective Cultivation of Plants
All around the world, many new varieties of cultivated plants were developed. Rice, wheat, and barley were improved in Asia; yams, peanuts, and gourds were selectively cultivated in Africa; corn, squash, peppers, and tomatoes, in the Americas.
Interestingly, there’s no record in prehistoric times of anyone in Europe doing selective cultivation. It was not universal, but very widely adopted around the world.
How Human Beings Inherit Traits
Not surprisingly, this idea of inherited traits was applied to human beings. Ancient scholars noted that certain diseases run in families. For example, hemophilia and certain kinds of mental disorders also ran in families.
Some societies also concluded that undesirable characteristics, such as dishonesty or sloth, cowardice, also ran in families; and this observation may have led, in some societies, to the caste system, where high-born and low-born actually represented a prediction of certain personality traits, which we certainly wouldn’t agree to today.
Aristotle’s Idea of Spontaneous Generation
The context of ancient thinking about genetics was quite different from today. The doctrine of spontaneous generation is a tenet of the teachings of Aristotle. It claimed that inanimate matter was imbued with a life force, so that life spontaneously arises around us all the time.
This idea hindered genetic understanding, because if maggots appear spontaneously, and other life forms can just occur from inanimate life, then somehow that information was contained in a kind of ether, in a way that you can’t say was physically passed from one cell to another. The relationship between flies and maggots, and indeed the dismantling of the spontaneous generation theory, therefore, was critical to genetic understanding.
Redi’s Experiment
An important step was taken by the Italian naturalist Francesco Redi, who lived from 1626 to 1697. In the year 1668, Redi published the results of a whole series of experiments that showed that meat that was kept isolated, and away from insects, never produced other insects; maggots did not form in this way. This helped discard one of the tenets of spontaneous generation, about maggots.
There were many other important contributions as well; some were made by the amateur Dutch scientist Antonie van Leeuwenhoek, who lived from 1632 to 1723. He was a contemporary of Redi and Robert Hooke; he also used microscopes, and was the first person to look through the microscope to try to understand the duplication of life, or the origin of life.
Over-ruling the Spontaneous Generation Theory
Van Leeuwenhoek was the first to observe microorganisms, single-celled organisms, in water. He observed the sperm cells, and also semen—the first to do that. He suggested that every sperm contains a complete, miniature human being, so that when the egg is fertilized, that human being is inserted into the egg, and starts to grow in that way.
Much of van Leeuwenhoek’s efforts were directed towards a refutation, then, of this doctrine of spontaneous generation; and it was his work, along with that of Redi and many other people, including Louis Pasteur who finally debunked that whole idea. Then, you had to contend with the fact that biological information was passed from one generation of cell to the next—a key tenet of the cell theory.
Common Questions about Classical Genetics Vs. Spontaneous Generation Theory
The history of genetics can be divided into three major eras. First came classical genetics: the study of genetics at the level of organisms and their traits. Then came cellular genetics, when microscopes became good enough that we could actually look inside the cell and see what was happening as cells divided. Finally, molecular genetics: looking at genetics at the scale of the molecule that contains the genetic code, DNA.
The context of ancient thinking about genetics was quite different from today. The doctrine of spontaneous generation is a tenet of the teachings of Aristotle. It claimed that inanimate matter was imbued with a life force, so that life spontaneously arises around us all the time.
Antonie van Leeuwenhoek, Francesco Redi, and Louis Pasteur, among others debunked the idea of spontaneous generation.
