Search results
Revolutionary United Front (RUF), guerrilla unit formed in 1991 in Sierra Leone whose actions created instability in the country that led to the overthrow of the government and a long civil war. The group later financed itself through control of the country’s diamond resources and for 11 years.
- Richard Mchugh
Sep 3, 2024 · All life tends to increase: more organisms are conceived, born, hatched, germinated from seed, sprouted from spores, or produced by cell division (or other means) than can possibly survive. Each organism so produced varies, however little, in some measurable way from its relatives.
- Overview
- Spontaneous generation
- The death of spontaneous generation
- The origin of primordial life
If a species can develop only from a preexisting species, then how did life originate? Among the many philosophical and religious ideas advanced to answer that question, one of the most popular was the theory of spontaneous generation, according to which, as already mentioned, living organisms could originate from nonliving matter. With the increasing tempo of discovery during the 17th and 18th centuries, however, investigators began to examine more critically the Greek belief that flies and other small animals arose from the mud at the bottom of streams and ponds by spontaneous generation. Then, when Harvey announced his biological dictum ex ovo omnia (“everything comes from the egg”), it appeared that he had solved the problem, at least insofar as it pertained to flowering plants and the higher animals, all of which develop from an egg. But Leeuwenhoek’s subsequent disquieting discovery of animalcules demonstrated the existence of a densely populated but previously invisible world of organisms that had to be explained.
The Italian physician and poet Francesco Redi was one of the first to question the spontaneous origin of living things. Having observed the development of maggots and flies on decaying meat, Redi in 1668 devised a number of experiments, all pointing to the same conclusion: if flies are excluded from rotten meat, maggots do not develop. On meat exposed to air, however, eggs laid by flies develop into maggots. Nonetheless, in 1745 support for spontaneous generation was renewed with the publication of An Account of Some New Microscopical Discoveries by the English naturalist and Roman Catholic divine John Turberville Needham. Needham found that large numbers of organisms subsequently developed in prepared infusions of many different substances that had been exposed to intense heat in sealed tubes for 30 minutes. Assuming that such heat treatment must have killed any previous organisms, Needham explained the presence of the new population on the grounds of spontaneous generation. The experiments appeared irrefutable until the Italian physiologist Lazzaro Spallanzani repeated them and obtained conflicting results. He published his findings around 1775, claiming that Needham had not heated his tubes long enough, nor had he sealed them in a satisfactory manner. Although Spallanzani’s results should have been convincing, Needham had the support of the influential French naturalist Buffon; hence, the matter of spontaneous generation remained unresolved.
If a species can develop only from a preexisting species, then how did life originate? Among the many philosophical and religious ideas advanced to answer that question, one of the most popular was the theory of spontaneous generation, according to which, as already mentioned, living organisms could originate from nonliving matter. With the increasing tempo of discovery during the 17th and 18th centuries, however, investigators began to examine more critically the Greek belief that flies and other small animals arose from the mud at the bottom of streams and ponds by spontaneous generation. Then, when Harvey announced his biological dictum ex ovo omnia (“everything comes from the egg”), it appeared that he had solved the problem, at least insofar as it pertained to flowering plants and the higher animals, all of which develop from an egg. But Leeuwenhoek’s subsequent disquieting discovery of animalcules demonstrated the existence of a densely populated but previously invisible world of organisms that had to be explained.
The Italian physician and poet Francesco Redi was one of the first to question the spontaneous origin of living things. Having observed the development of maggots and flies on decaying meat, Redi in 1668 devised a number of experiments, all pointing to the same conclusion: if flies are excluded from rotten meat, maggots do not develop. On meat exposed to air, however, eggs laid by flies develop into maggots. Nonetheless, in 1745 support for spontaneous generation was renewed with the publication of An Account of Some New Microscopical Discoveries by the English naturalist and Roman Catholic divine John Turberville Needham. Needham found that large numbers of organisms subsequently developed in prepared infusions of many different substances that had been exposed to intense heat in sealed tubes for 30 minutes. Assuming that such heat treatment must have killed any previous organisms, Needham explained the presence of the new population on the grounds of spontaneous generation. The experiments appeared irrefutable until the Italian physiologist Lazzaro Spallanzani repeated them and obtained conflicting results. He published his findings around 1775, claiming that Needham had not heated his tubes long enough, nor had he sealed them in a satisfactory manner. Although Spallanzani’s results should have been convincing, Needham had the support of the influential French naturalist Buffon; hence, the matter of spontaneous generation remained unresolved.
After a number of further investigations had failed to solve the problem, the French Academy of Sciences offered a prize for research that would “throw new light on the question of spontaneous generation.” In response to that challenge, Louis Pasteur, who at that time was a chemist, subjected flasks containing a sugared yeast solution to a variety of conditions. Pasteur was able to demonstrate conclusively that any microorganisms that developed in suitable media came from microorganisms in the air, not from the air itself, as Needham had suggested. Support for Pasteur’s findings came in 1876 from the English physicist John Tyndall, who devised an apparatus to demonstrate that air had the ability to carry particulate matter. Because such matter in air reflects light when the air is illuminated under special conditions, Tyndall’s apparatus could be used to indicate when air was pure. Tyndall found that no organisms were produced when pure air was introduced into media capable of supporting the growth of microorganisms. It was those results, together with Pasteur’s findings, that put an end to the doctrine of spontaneous generation.
When Pasteur later showed that parent microorganisms generate only their own kind, he thereby established the study of microbiology. Moreover, he not only succeeded in convincing the scientific world that microbes are living creatures, which come from preexisting forms, but also showed them to be an immense and varied component of the organic world, a concept that was to have important implications for the science of ecology. Further, by isolating various species of bacteria and yeasts in different chemical media, Pasteur was able to demonstrate that they brought about chemical change in a characteristic and predictable way, thus making a unique contribution to the study of fermentation and to biochemistry.
In the 1920s the Russian biochemist Aleksandr Oparin and other scientists suggested that life may have come from nonliving matter under conditions that existed on primitive Earth, when the atmosphere consisted of the gases methane, ammonia, water vapour, and hydrogen. According to that concept, energy supplied by electrical storms and ultraviolet light may have broken down the atmospheric gases into their constituent elements, and organic molecules may have been formed when the elements recombined.
Some of those ideas have been verified by advances in geochemistry and molecular genetics; experimental efforts have succeeded in producing amino acids and proteinoids (primitive protein compounds) from gases that may have been present on Earth at its inception, and amino acids have been detected in rocks that are more than three billion years old. With improved techniques it may be possible to produce precursors of or actual self-replicating living matter from nonliving substances. But whether it is possible to create the actual living heterotrophic forms from which autotrophs supposedly developed remains to be seen.
May 3, 2016 · How did complex systems of chemical reactions on the prebiotic Earth lead to living organisms? But to tackle it, we need to start from a philosophical point of view and define some of the functions an organism needs to be called living.
- Paul Maclellan
Sep 27, 2012 · The attributes of the first living organisms are also unknown. They were not like extant microbes, but probably simpler than any cell now alive, and may have lacked not only protein-based catalysis, but also perhaps even the familiar genetic macromolecules, with their ribose-phosphate backbones.
- Antonio Lazcano
- alar@ciencias.unam.mx
- 2012
Sep 19, 2022 · The origin of life on Earth stands as one of the great mysteries of science. Various answers have been proposed, all of which remain unverified. To find out if we are alone in the galaxy, we will need to better understand what geochemical conditions nurtured the first life forms.
People also ask
What did the RUF do in Sierra Leone?
What happened to the RUF in 1992?
Who fought the AFRC & RUF?
When did the RUF START disarmament?
Feb 23, 2010 · The first characteristic of living matter is the presence of “vital orgasm”, a particular force that maintains molecules separated in spite of universal attraction. The causes of this “vital orgasm” are the uncontainable fluids: electricity and heat.
