by bystander » Wed Apr 23, 2008 2:37 pm
harry wrote:Knowing this we look at the fossil evidence and we see that viruses were the first to evolve.
Simple DNA structures.
It is unlikely viruses evolved first. Viruses cannot replicate w/o a host organism. Some bioligist do not consider viruses to even be a life form. Some viruses are RNA based, not DNA. Bacteria were probably the first life forms, then their predators, bateriophages.
http://en.wikipedia.org/wiki/Virus
Viruses have been described as "organisms at the edge of life", but argument continues over whether viruses are truly alive. According to the United States Code, they are considered microorganisms in the sense of biological weaponry and malicious use. Scientists, however, are divided. Things become more complicated as they look at viroids and prions. Viruses resemble other organisms in that they possess genes and can evolve in infected cells by natural selection. They can reproduce by creating multiple copies of themselves through self-assembly.
Viruses do not have a cell structure (regarded as the basic unit of life), although they do have genes. Additionally, although they reproduce, they do not self-metabolize and require a host cell to replicate and synthesize new products. However, bacterial species such as Rickettsia and Chlamydia are considered living organisms but are unable to reproduce outside a host cell.
An argument can be made that accepted forms of life use cell division to reproduce, whereas viruses spontaneously assemble within cells. The comparison is drawn between viral self-assembly and the autonomous growth of non-living crystals. Virus self-assembly within host cells has implications for the study of the origin of life, as it lends credence to the hypothesis that life could have started as self-assembling organic molecules.
If viruses are considered alive, then the criteria specifying life will have to exclude the cell. If viruses are said to be alive, the question could follow of whether even smaller infectious particles, such as viroids and prions, are alive.
[quote="harry"]Knowing this we look at the fossil evidence and we see that viruses were the first to evolve.
Simple DNA structures.[/quote]
It is unlikely viruses evolved first. Viruses cannot replicate w/o a host organism. Some bioligist do not consider viruses to even be a life form. Some viruses are RNA based, not DNA. Bacteria were probably the first life forms, then their predators, bateriophages.
[url]http://en.wikipedia.org/wiki/Virus[/url]
[quote]Viruses have been described as "organisms at the edge of life", but argument continues over whether viruses are truly alive. According to the United States Code, they are considered microorganisms in the sense of biological weaponry and malicious use. Scientists, however, are divided. Things become more complicated as they look at viroids and prions. Viruses resemble other organisms in that they possess genes and can evolve in infected cells by natural selection. They can reproduce by creating multiple copies of themselves through self-assembly.
Viruses do not have a cell structure (regarded as the basic unit of life), although they do have genes. Additionally, although they reproduce, they do not self-metabolize and require a host cell to replicate and synthesize new products. However, bacterial species such as Rickettsia and Chlamydia are considered living organisms but are unable to reproduce outside a host cell.
An argument can be made that accepted forms of life use cell division to reproduce, whereas viruses spontaneously assemble within cells. The comparison is drawn between viral self-assembly and the autonomous growth of non-living crystals. Virus self-assembly within host cells has implications for the study of the origin of life, as it lends credence to the hypothesis that life could have started as self-assembling organic molecules.
If viruses are considered alive, then the criteria specifying life will have to exclude the cell. If viruses are said to be alive, the question could follow of whether even smaller infectious particles, such as viroids and prions, are alive.[/quote]