why don't we believe in the "spontaneous generation" anymore?

Question

in more specific i am searching for 'why we don't think that way anymore'?

Answer 1

What is "Spontaneous generation"?-----

Answer--Classical notions of abiogenesis, now more precisely known as spontaneous generation, held that complex, living organisms are generated by decaying organic substances, e.g. that mice spontaneously appear in stored grain or maggots spontaneously appear in meat.

FOR EXAMPLE -

1 ) According to Aristotle it was a readily observable truth that aphids arise from the dew which falls on plants, fleas from putrid matter, mice from dirty hay, and so forth.

OBJECTION-

In the 17th century such assumptions started to be questioned; such as that by Sir Thomas Browne in his Pseudodoxia Epidemica, subtitled Enquiries into Very many Received Tenets, and Commonly Presumed Truths, of 1646, an attack on false beliefs and "vulgar errors."

SUPPORT -

His conclusions were not widely accepted, e.g. his contemporary,

Alexander Ross wrote: "To question this (i.e., spontaneous generation) is to question reason, sense and experience. If he doubts of this let him go to Egypt, and there he will find the fields swarming with mice, begot of the mud of Nylus, to the great calamity of the inhabitants."

EXPERIMENTAL EVIDENCE WENT AGAINST -

However, experimental scientists continued to decrease the conditions within which the spontaneous generation of complex organisms could be observed.

The first step was taken by the Italian Francesco Redi, who, in 1668, proved that no maggots appeared in meat when flies were prevented from laying eggs.

From the seventeenth century onwards it was gradually shown that, at least in the case of all the higher and readily visible organisms, the previous sentiment regarding spontaneous generation was false.

The alternative seemed to be omne vivum ex ovo: that every living thing came from a pre-existing living thing (literally, from an egg).

THEREFORE THE SUPPORT FOR THAT HYPOTHESIS BEGAN TO WANE

Then in 1683 Antoni van Leeuwenhoek discovered bacteria, and it was soon found that however carefully organic matter might be protected by screens, or by being placed in stoppered receptacles, putrefaction set in, and was always accompanied by the appearance of myriad bacteria and other low organisms.

As knowledge of microscopic forms of life increased, so the apparent realm of abiogenesis increased, and it became tempting to hypothesize that while abiogenesis might not take place for creatures visible to the naked eye, at the microscopic level, living organisms continually arose from inorganic matter.

In 1768 Lazzaro Spallanzani proved that microbes came from the air, and could be killed by boiling.

FINAL BLOW TO THAT HYPOTHESIS -

Yet it was not until 1862 that Louis Pasteur performed a series of careful experiments which proved that organisms such as bacteria and fungi do not appear in nutrient rich media of their own accord in non-living material.

Answer 2

Pasteur disproved spontaneous generation when he did the experiments with bacterial growth in broth cultures.

See explanations of Pasteur's experiments:
http://www.accessexcellence.org/RC/AB/BC/Spontaneous_Generation.html

Answer 3

because we believe in biogenesis