What is the role of chance in scientific discovery?


“The theory that chromosome behaviour accounts for Mendel’s principles of segregation an independent assortment is known as the Sutton-Boveri chromosome theory of inheritance. Sutton and Boveri were two scientists who worked independently, but it was Sutton who was the first to publish his research. Boveri studied Parascaris equorum, a roundworm with large cells, containing only two pairs of chromosomes.
Historians of science have pointed out that Sutton was aided by the serendipitous use of the research organism, Brachystola magna, a grasshopper. Sutton began his research in Kansas and the great abundance of grasshoppers in that state contributed to its use as a research organism. Brachystola magna had eleven pairs of chromosomes. This made it much easier to distinguish individual chromosomes by their size and shape. Using similar techniques to Boveri, he documented the configuration of chromosomes undergoing meiosis, and made the observation that each chromosome has a well-defined shape that is conserved in each cell generation. This prompted Sutton to proclaim that ‘chromosomes may constitute the physical basis of the Mendelian law of heredity.'”

(BIOLOGY Course Companion, 2014)

Walter Sutton and Theodor Boveri

Sutton-Boveri chromosome theory of inheritance:

chromosome theory

To better understand what the role of chance is, you have to know what it means. This is the definition according to the Oxford dictionary:

ChanceThe occurrence of events in the absence of any obvious intention or cause

A word which is commonly used to describe “luck” in a scientific discovery is serendipity. It is an unexpected event that occurs due to chance.

SerendipityThe occurrence and development of events by chance in a happy or beneficial way

This word was invented by Horace Walpole in 1754. He explained an unexpected discovery he had made in reference to a Persian fairy tale, The Three Princes of Serendip. Walpole stated that the princes were “always making discoveries, by accidents and sagacity, of things which they were not in quest of”

“Scientists are not passive recipients of the unexpected; rather, they actively create the conditions for discovering the unexpected and have a robust mental toolkit that makes discovery possible.”

– Kevin Dunbar and Jonathan Fugelsang

Kevin Dunbar estimates that 30% – 50% scientific discoveries are accidental. Along with Fugelsang, Dunbar suggests that the process of scientific discovery often starts when a researcher finds mistakes in their experiment. These unexpected results lead a researcher to try and fix what they think is an error in their procedure. Eventually, the researcher decides that the “error” is too persistent and systematic to be a coincidence so he or she will begin to think of theoretical explanations for the “error”.

“In the fields of observation, chance only favours the mind which is prepared”

– Louis Pasteur
Portrait of Louis Pasteur

Here, Pasteur was speaking about Oersted, a Danish physicist’s, almost “accidental” way in which he discovered the basic principles of electro-magnetism. He then “by chance” came upon a significant observation:

through a microscope, he observed that healthy fermentation produced round globules and they lengthened as alteration began, becoming very long and slender at the point they became lactic.

This allowed manufacturers to observe the health of fermentation during their manufacturing processes to avoid common failures during fermentation. Pasteur began going down a path that would develop into the science of Microbiology while revolutionizing Chemistry at the same time.

Scientists conduct experiments to attempt to prove a hypothesis. The chance of making an accidental discovery is amplified when no conclusive results are presented. However, it is not during this accidental moment that an actual discovery occurs: the scientist must be able, with prepared mind, to interpret the accidental observation.

Chance and a prepared mind are linked in the process of making scientific discoveries. A “prepared mind” is one that is constantly curious and persistent, always questioning everything. When the result of an experiment is unexpected or unusual, a prepared mind doesn’t simply discard the result and start the experiment again, but ponders and investigates the unusual observation and why the result turned out the way it did.


Serendipity is a common occurrence throughout the history of scientific discovery such as Alexander Fleming’s accidental discovery of penicillin in 1928.


Probably the most famous serendipitous event reported in science.

Fleming’s discovery of penicillin began when he was investigating a group of petri dishes on his workbench. They contained colonies of a bacterium called Staphylococcus which Fleming had deliberately placed in the dishes. He found that one of the dishes had become contaminated by a mold, and he noticed that there was a clear area around the mold.

penicillin mold

Instead of cleaning or discarding the petri dish and ruling out the contamination as a “mistake”, he decided to investigate why the clear area had appeared. Eventually, he discovered that the mold, a species of Penicillium, was making an antibiotic that killed the bacteria around it. Fleming named the antibiotic penicillin. It soon became an extremely important medicine for fighting infections.

NPG x136472; Alexander Fleming by Howard Coster

In conclusion, when you are doing research for discoveries, in actuality you are looking for the unexpected. Research is mostly considered successful when something occurs that you didn’t think was or could happen. Chance/serendipity is usually defined as an accidental discovery, yet that all depends on how an individual understands accidents to validate their opinion on chance. Persistence is key in scientific discovery to make the serendipitous “accident” valid since re-testing to achieve answers is essential. Normally, serendipity is the result of a stimulus, not just something that happens in the moment, this provides an incentive to explore science more deeply and allows scientists to go in another direction for their original goal widening their knowledge so that the rest of the world can learn and benefit.

Here is an entertaining video showing “10 accidental inventions” you never expected:


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