Elegant biology

Beauty, as we know, is in the eye of the beholder, and the beholder finds beauty in many different things. Scientists are no exception. What can be "beautiful" in a mathematical equation, in a physical theory, or in an experiment?

Yonat Ashhar, Galileo

Surprisingly, concepts like beauty and elegance come up again and again not only in conversations between scientists but also in textbooks, and even in scientific articles. We will try to answer here the question of what is actually a "beautiful" biological experiment, through a review of three particularly beautiful classical experiments.

What requirements does an experiment have to meet in order to win the title "beautiful"?

First of all, it should be at least relatively simple, so that anyone who reads it will immediately understand what it is about. Usually it is a short series of experiments - or even one experiment - that answers a specific question. A study based, for example, on the careful collection of facts over twenty years, can be useful and important, but it is not elegant.

A good experiment usually tries to solve a certain problem from a new angle, using familiar tools but from a new and original way of thinking. An experiment whose main purpose is the use of new equipment, operated in a way known for a long time, will not be awarded such a title.
On top of that, a particularly important point is the unequivocal result of the experiment. The classic elegant experiments, such as those described below, were done in order to decide between two opposing theories, or to confirm a certain claim. Their power stems from their ability to persuade: each of them, at the time, caused many to "take sides" and support the claims of the researchers who performed the experiment.
Meat creates a maggot, rot creates a bacterium - Louis Pasteur and the death of the theory of spontaneous creation

In 1668, an Italian doctor named Francesco Redi placed several jars on the windowsill of his home. There was rotten meat in the jars. Some of the jars were completely closed, some were wrapped in gauze, and the rest were left open. This is how the experiment was planned and carried out, which many consider to be the first biological experiment that met scientific standards.

What was so special about this simple experiment, and what was it trying to test? Reddy examined the theory called "spontaneous creation", according to which animals can be created spontaneously from inanimate substances. This theory is not as ridiculous as it sounds to us today; In fact, it fits nicely with the observations made in those days. These observations showed, for example, that after the rain the ground turns into mud and frogs appear, which were not there before. Mice appeared similarly in barns, and flies - near carcasses or in butcher shops. Hence the claim that mud creates frogs, that grain kernels create mice, that rotten meat creates flies, and so on. This is a completely scientific claim, based on observations - and can also be tested, through an experiment like the one performed by Reddy.

If the theory of spontaneous selection is correct, then the flies will develop in all the jars - they will simply be created from the meat. But if flies are created solely from other flies, as Reddy thought, denying flies access to the meat would prevent the creation of new flies inside the jar. And so it was: in the closed jars no maggots appeared and no flies developed. On top of that, Reddy reported that the flies laid eggs on the cheesecloth that covered some of the jars, and some of them fell through it into the meat - therefore, some flies were seen in these jars. Based on this experiment, Reddy determined that all the flies that appeared in the jars were created from eggs laid by adult flies, and not from the meat itself.

What was special about this experiment - and it was the thing that earned it the title of "the first biological experiment" - was the use made, perhaps for the first time, of criticism; Reddy was not satisfied with stating that there were no flies in the closed jars, but showed that under exactly the same conditions, apart from the condition he tested - the flies' accessibility to the meat - the flies did appear. Since then, the control experiment is one of the most important principles in the field of life sciences.

This experiment and others that followed effectively eliminated the theory of spontaneous creation of animals: it was established quite satisfactorily that only animals produce more animals. But then a new player entered the game - the microscope.

see and believe

At the end of the 17th century and the beginning of the 18th century, microscopes were built and perfected with the help of which microorganisms could be seen, and these were quickly discovered almost everywhere - from water drops to fruits. Many microorganisms in particular were seen in rotten meat and fermenting fruit, and the question arose: where do these life forms come from? Are the microorganisms that cause decay and fermentation, or maybe the other way around - it is the rot that creates them?

This debate was more difficult to resolve, and the dispute continued for about 150 years. Many experiments were designed to settle the controversy, and most of them were quite similar to Reddy's simple experiment. In 1748, John T. Needham took jars with meat broth in them, closed them, boiled the liquid - so that every microorganism that was there and could produce more microorganisms was supposed to die - and showed that nevertheless microorganisms were formed in them. According to him, this was proof that microorganisms are formed spontaneously from meat broth. Less than twenty years passed until an Italian scientist - Lazaro Spallanzani - showed that Needham's jars were not properly sterilized, and that nothing was formed in jars that were heated more thoroughly. But that wasn't the end of the story either; Supporters of spontaneous creation claimed against Splenzani that the prolonged heating spoiled the air inside the jar, and perhaps also damaged the creative power of the meat broth itself. In a later period, claims were heard against the entire closed jar method: organisms cannot develop in them, it was claimed, simply because they do not have enough oxygen.

In 1860, the key player in this drama - Louis Pasteur - appeared on stage. Pasteur - one of the greatest French scientists, known today as the "father of microbiology" - planned and carried out one of the most elegant and convincing experiments in the history of biology, and in the end definitively eliminated the theory of spontaneous creation.

In the same year, one of the biggest supporters of spontaneous creation - Felix Pouchet - presented what was supposed to be the experiment that would decide the debate, in favor of his side of course. At this point, the French Academy of Sciences presented a sort of "open competition": a prize for anyone who could present an experiment that could resolve the controversy. Pasteur could not refuse such a challenge - he immediately approached the craft.

The beginning was quite banal: Pasteur took a glass container and filled it with meat broth. He then heated the neck of the container until he could shape the glass to his liking, twisting it into an S shape.

The next step was boiling the meat broth. The boiling served a dual purpose: it both concentrated the liquid, and caused steam to escape through the opening. After the liquid cooled, the vapor condensed on the neck of the long container, and moisture accumulated especially at its lowest point (point a). When air from the outside entered the tank, the air and dust accumulated at that point, and the water that accumulated there also served as a kind of "air filter" - so that microorganisms could not enter and reach the soup, and remained at the bottom of the "neck". Nothing grew in the meat-broth, until Pasteur broke the neck and allowed unfiltered air to enter - then the broth was filled with microorganisms.
Yonat Ashhar is a master's student in the Department of Plant Sciences at the Weizmann Institute