Professor Manuel Varela: Amazing Scientists REDI

Jan 24, 2017 by

An Interview with Professor Manuel Varela: Amazing Scientists REDI

Michael F. Shaughnessy

1) Professor Varela, I would like to ask you some questions about Francesco Redi and his contributions to science. Can you provide some background as to his birth (when and where) and his early endeavors and education and experience?

Thank you for inquiring about the amazing scientist Dr. Francesco Redi. He was born in the town of Arezzo, Italy, on February 18, 1626. In his early years, he was educated in Florence at a Jesuit-run school, which taught mainly theology. When Redi turned about 15 years of age, he moved to the University of Pisa, where he ultimately earned his doctorate degrees in medicine and philosophy in 1647.  Dr. Redi subsequently became the personal physician to the Grand Duke of Tuscany, Ferdinand II, and later to his successor, Cosimo III.

2) Now, I may be wrong, but Redi was apparently the first to test Aristotle’s “spontaneous generation” ideas– using flies—How did this all come about and why is it important in the realm of science?

You are certainly correct about Dr. Redi being the first scientist to experimentally challenge the idea of spontaneous generation.  In fact, Dr. Redi has the distinction of apparently publishing one of the very first, if not the first, experimentally-based paper dealing with the biological sciences, complete with proper controls.

The concept of spontaneous generation originated with Aristotle back in 343 B.C., when he postulated that living beings could simply generate themselves into existence spontaneously out of non-living materials, a notion that is to this day referred to as abiogenesis (i.e., life arises out of non-life).  It is generally believed that Aristotle himself actually invoked, as an example, the flies as spontaneously generating themselves straight out of meat that’s left to sit out, open to the air.  Although at first glance one might erroneously envisage how this might somehow be true, being that if one does leave meat exposed to air, one might certainly see flies “emerging spontaneously” from the meat. Incidentally, according to the theory, air was believed to be a “vital force” that was necessary for spontaneous generation to manifest itself.  That is, air was critical to the process.

The facts need to be taken into account, however, that flies will actually land on the exposed meat, lay their eggs and hatch, and be mistakenly interpreted by observers to mean that spontaneous generation has occurred in which flies arise directly from the non-living meat. This incorrect spontaneous generation concept was nonetheless widely believed for many centuries to be completely true, believed even well into the 19th century. Spontaneous generation is certainly not true, and Dr. Redi was the first individual in history to provide experimental evidence against it.

3) What other contributions was he known for and why is this one still studied?

Dr. Redi is known also in scientific circles for his work as an early pioneer in the field of parasitology. He studied a particular type of parasitic worm known as the helminth, a kind of tapeworm.  Worm parasites, such as the helminthes, infect the guts of animals, including those of humans and thrive at the expense of their unfortunate animal hosts. Parasites are unable to live totally on their own, and they thus require a living host that has all the biological workings necessary for life and which a parasite lacks. Thus, parasites which infect a host benefit in terms of growth while their hosts, in turn, suffer from the loss of nutrients, etc. Lastly, one thing I neglected to mention is that in some of the literature dealing with scientific history, Dr. Redi is considered to be the father of parasitology.

4) As I recall “dropsfilia” ( fruit flies ) were central to his methods- why is this important for budding scientists to know about and why is it so critical ?

Interestingly, Dr. Redi read the ancient works of Aristotle and was aware of his spontaneous generation theory, along with the putative involvement of the flies, meat, and air.  Redi also read the publications of both Hooke and Leeuwenhoek.  So, Redi was especially aware of the observations that were made about microbes and other specimens by these earlier investigators using their scopes. Furthermore, Redi knew about the writings of William Harvey, who essentially refuted the theory. In particular, however, Redi was intrigued by Leeuwenhoek’s published descriptions of flies at the microscopic level; there was no doubt that their body structures were complex, leading Leeuwenhoek to reason, thus, that flies reproduced sexually by laying eggs, which would hatch and then release progeny flies. This reproduction theory, however, flew in the face of the firmly established and ongoing spontaneous generation theory. For instance, if flies spontaneously generated themselves, then there was then no apparent need for sexual reproduction and, consequently, no need for their complicated body structures seen in the flies. In summary, the questions were as follows.  Did flies reproduce sexually, or did they simply spontaneously generate?  These were the main issues concerning Dr. Redi and his historically famous work.

In 1668, Dr. Redi described in his newly published paper how he put to the test the idea of spontaneous generation.  He had set up several flasks, all with meat placed into each of them.  In one flask the meat was sealed airtight, preventing access to flies and the outside air, with its “vital force.” Another flask was covered with a gauze mesh that kept flies out but still allowed air exposure to occur upon the meat within the flask. The last flask was left totally uncovered and open directly to both air and flies. In the first two flasks, both open to air, no flies arose from the meat. In contrast, in the open flask which allowed air and flies open access, Redi described that he observed flies landing on the meat, likely laying their eggs, and the subsequent hatching of the fly eggs. Redi further noted that the fly larvae developed into young flies on the uncovered meat, and he further observed the flies simply flying away. Because no flies spontaneously arose out of the meat within either of the sealed or the gauze-covered flasks, Redi concluded, correctly, that spontaneous generation did not occur, at least in flies.  This famous experiment is still introduced in virtually all modern textbooks of Microbiology. It is also used as a good example of how to put the modern scientific method of inquiry to work when testing new ideas.

5) What are some interesting facts or details about this person and his life and contributions?

It may interest you and your readers to know that Dr. Redi had other intellectual interests. Apparently, he was recognized as a talented poet.  He also pursued independent studies in the areas of linguistics, language dialects, and literature.

6) What have I neglected to ask about this interesting scientist?

I think it is fascinating to consider how Redi’s famous fly experiment was received in his time and thereafter.  On the one hand, an interesting outcome of the famous Redi fly experiment is that few people at the time were convinced of the fallibility of the spontaneous generation theory. Many people still believed in it. You’ll recall that the idea had been resolutely established and firmly ingrained since ancient times, with Aristotle. So it was difficult to just let the idea go. In fact, Redi himself still thought that microbes generated spontaneously, even if his flies didn’t.

An additional confounding factor was the work of another investigator, John Needham, who tested the spontaneous generation theory in microbes. Unfortunately, Needham’s work still showed microbes apparently thriving in mutton gravy broth even after having been heated with a direct flame. The unfortunate happenstance is that Needham had had contaminating heat-resistant microbes, providing inaccurate evidence in support of spontaneous generation.

One the other hand, in 1767 Lorenzo Spallanzani, a well-respected clergyman and scientist in his own right, proposed that the tiny microbes landed on the mutton gravy broth and used it to grow, thereby refuting the spontaneous generation theory. The microbes were simply floating around in the air.  The controversy continued, setting the stage for the spontaneous generation theory to remain intact well into the 19th century, until the definitive experiments of the great Prof. Louis Pasteur.

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