Flies and Spontaneous Generation

One of Redi's most famous experiments investigated spontaneous generation. At the time, scientists believed in the Aristotelian idea of abiogenesis, in which
living organisms arose from non-living matter. People believed rotting meat spontaneously produced maggots over time. However, Redi read a book by William
Harvey on generation in which Harvey speculated that insects, worms, and frogs might arise from eggs or seeds too tiny to be seen. Redi devised and performed
the now-famous experiment in which six jars, half left in open air and half covered with fine gauze that permitted air circulation but kept out flies, were filled
with either an unknown object, a dead fish, or raw veal. The fish and veal rotted in both groups, but maggots only formed in the jars open to air. No maggots
developed in the jar with the unknown object.

He performed other experiments with maggots, including one where he placed dead flies or maggots in sealed jars with meat and observed living maggots did
not appear. However, when he placed living flies were placed in a jar with meat, maggots did appear. Redi concluded maggots came from living flies, not from
rotting meat or from dead flies or maggots.

The experiments with maggots and flies were important not only because they refuted spontaneous generation, but also because they used control groups,
applying the scientific method to test a hypothesis.

By 

Anne Marie Helmenstine, Ph.D.Updated on September 09, 2018

Francesco Redi’s Contributions to Science

Redi maintained a lifelong loyalty to the Jesuits, but word reached him of the importance Galileo placed on gathering evidence to support scientific ideas.
Galileo’s viewpoint sounded so appropriate that Redi applied it in his own investigations.

Also, while studying medicine in Pisa, Redi learned about the rational experiments carried out by William Harvey. These experiments provided Harvey with the
data he needed to correctly describe blood circulation around the body for the first time. Redi was highly impressed by Harvey’s research work.

Spontaneous Generation

Aristotle had also promoted the idea that life is generated spontaneously: he said simpler lifeforms such as worms and maggots need no parents – they emerge
alive from the earth and from rotting organic matter. This idea had been accepted for over 2,000 years.

Again, Redi used experiments to research this subject. He observed that flies laid eggs on meat. These eggs hatched into maggots. If the meat was protected
from flies, no eggs were laid and no maggots appeared.

He described his work in 1668 in Experiments on the Generation of Insects.

“And although it can be observed daily that an enormous number of worms are produced in dead bodies and decayed plants, I feel inclined to
believe that these worms are all generated by insemination.”

FRANCESCO REDI

Experiments on the Generation of Insects, 1668

A little over a decade later, Antonie van Leeuwenhoek confirmed Redi’s maggot and fly work, observing the entire lifecycle. In the 1830s, Theodor
Schwann showed that microorganisms do not spontaneously generate. Finally, in 1862, Louis Pasteur completely killed off the idea of spontaneous generation in
mainstream science. Redi had been the first person to use experiments to show fellow scientists the path, but it took them a long time to follow it to its natural
conclusion.

In addition to his refutation of spontaneous generation, Experiments on the Generation of Insects contained Redi’s detailed drawings of a large variety of insects,
eggs, and maggots, such as these below.
Redi’s drawing of a donkey louse
under the microscope

Redi’s drawing of an ant

The Slow Death of Spontaneous Generation (1668-1859)

Russell Levine and Chris Evers

From the time of the ancient Romans, through the Middle Ages, and until the late nineteenth century, it was generally accepted that some life forms
arose spontaneously from non-living matter. Such "spontaneous generation" appeared to occur primarily in decaying matter. For example, a
seventeenth century recipe for the spontaneous production of mice required placing sweaty underwear and husks of wheat in an open-mouthed jar,
then waiting for about 21 days, during which time it was alleged that the sweat from the underwear would penetrate the husks of wheat, changing
them into mice. Although such a concept may seem laughable today, it is consistent with the other widely held cultural and religious beliefs of the
time.

The first serious attack on the idea of spontaneous generation was made in 1668 by Francesco Redi, an Italian physician and poet. At that time, it was
widely held that maggots arose spontaneously in rotting meat. Redi believed that maggots developed from eggs laid by flies. To test his hypothesis,
he set out meat in a variety of flasks, some open to the air, some sealed completely, and others covered with gauze. As he had expected, maggots
appeared only in the open flasks in which the flies could reach the meat and lay their eggs.

This was one of the first examples of an experiment in the modern sense, in which controls are used. In spite of his well-executed experiment, the
belief in spontaneous generation remained strong, and even Redi continued to believe it occurred under some circumstances. The invention of the
microscope only served to enhance this belief. Microscopy revealed a whole new world of organisms that appeared to arise spontaneously. It was
quickly learned that to create "animalcules," as the organisms were called, you needed only to place hay in water and wait a few days before
examining your new creations under the microscope.

The debate over spontaneous generation continued for centuries. In 1745, John Needham, an English clergyman, proposed what he considered the
definitive experiment. Everyone knew that boiling killed microorganisms, so he proposed to test whether or not microorganisms appeared
spontaneously after boiling. He boiled chicken broth, put it into a flask, sealed it, and waited - sure enough, microorganisms grew. Needham claimed
victory for spontaneous generation.

An Italian priest, Lazzaro Spallanzani, was not convinced, and he suggested that perhaps the microorganisms had entered the broth from the air after
the broth was boiled, but before it was sealed. To test his theory, he modified Needham's experiment - he placed the chicken broth in a flask, sealed the
flask, drew off the air to create a partial vacuum, then boiled the broth. No microorganisms grew. Proponents of spontaneous generation argued that
Spallanzani had only proven that spontaneous generation could not occur without air.

The theory of spontaneous generation was finally laid to rest in 1859 by the young French chemist, Louis Pasteur. The French Academy of Sciences
sponsored a contest for the best experiment either proving or disproving spontaneous generation. Pasteur's winning experiment was a variation of the
methods of Needham and Spallanzani. He boiled meat broth in a flask, heated the neck of the flask in a flame until it became pliable, and bent it into the
shape of an S. Air could enter the flask, but airborne microorganisms could not - they would settle by gravity in the neck. As Pasteur had expected, no
microorganisms grew. When Pasteur tilted the flask so that the broth reached the lowest point in the neck, where any airborne particles would have
settled, the broth rapidly became cloudy with life. Pasteur had both refuted the theory of spontaneous generation and convincingly demonstrated that
microorganisms are everywhere - even in the air.

Some Personal Details and the End

After studying literature at school, Redi remained a lifelong enthusiast, building a collection of many old manuscripts. He was also a celebrated poet, famous for
his lengthy work Bacchus in Tuscany, dedicated to the joy of wine drinking.

According to Bigelow, (see further reading) Redi did not marry and had no children of his own, although he did have nephews. According to Hunt, Redi had a
least one son, who achieved some renown in literature. If Redi married, the name of his wife has been lost in the mists of time.

From an early age Redi was prone to hypochondria, but took comfort from his personal belief that hypochondriacs seldom die at an early age. In his later years
he suffered from epilepsy.

Francesco Redi died at the age of 71 on March 1, 1697 in Pisa. He was buried in his hometown of Arezzo.
The Duke of Tuscany, Cosmo III, to whom Redi had been a valued physician struck three medals to honor Redi: one for his work in medicine; one for his
contributions to natural history; and one for his Bacchanalian poem.

Origin of Life: Spontaneous Generation

Spontaneous Generation

Origin of Life

 Introduction

 Spontaneous Generation

 Early Earth Environment

It was once believed that life could come from nonliving things, such as mice from corn, flies from bovine manure, maggots from rotting meat, and fish from the
mud of previously dry lakes. Spontaneous generation is the incorrect hypothesis that nonliving things are capable of producing life. Several experiments have
been conducted to disprove spontaneous generation; a few of them are covered in the sections that follow.

Redi's Experiment and Needham's Rebuttal

In 1668, Francesco Redi, an Italian scientist, designed a scientific experiment to test the spontaneous creation of maggots by placing fresh meat in each of two
different jars. One jar was left open; the other was covered with a cloth. Days later, the open jar contained maggots, whereas the covered jar contained no
maggots. He did note that maggots were found on the exterior surface of the cloth that covered the jar. Redi successfully demonstrated that the maggots came
from fly eggs and thereby helped to disprove spontaneous generation. Or so he thought.

In England, John Needham challenged Redi's findings by conducting an experiment in which he placed a broth, or gravy, into a bottle, heated the bottle to kill
anything inside, then sealed it. Days later, he reported the presence of life in the broth and announced that life had been created from nonlife. In actuality, he
did not heat it long enough to kill all the microbes.

Excerpted from The Complete Idiot's Guide to Biology © 2004 by Glen E. Moulton, Ed.D.. All rights reserved including
the right of reproduction in whole or in part in any form. Used by arrangement with Alpha Books, a member of Penguin
Group (USA) Inc.