Scientific theories are never certain. As quoted from the Scientific American page, a scientific theory itself is a collection of facts that can be observed and tested, and compiled over a long period of time by many scientists. Therefore, they can always be proven or disproved.

However, if we dig deeper into history, we will find some crazy theories that were accepted as scientific fact. For example, it was once believed that the traits of an ex could be transferred from a woman to children she had from another man. That theory, and eight others, are discussed below. Here's an explanation.

 1. The miasma theory

The miasma theory is a theory that states that diseases such as cholera, chlamydia, or the Black Death are caused by miasma, a type of "bad air." According to this theory, miasma originates from decaying organic matter.

2. Humoralisme

 

Humoralism, or humorism is a medical system that explains the structure and workings of the human body, which was adopted by the Ayurvedic medical system from India, philosophers and doctors from Ancient Rome and Greece, assuming that excess or deficiency of one of the four body fluids ) in a person known as humor (fluid)  has a direct effect on his health and temperament.

3. Preformasionisme

In the history of biology, preformationism was the once popular theory that organisms developed from miniature versions of themselves. Rather than assemble from parts, proponents of this theory believe that living forms existed, actually, before their development.