Could the two be one and the same? Enquiring minds want to know. Dibassey  
I'm trying to help you in your lifetime of angst. We may discover something  
together with Suntou. Avogadro's contemporaries thought he were silly too.  
Haruna. And he never obtained an invite to the infamous gaseous conference in  
Nouackchott.
 
 
Ed Rybicki, a virologist at the University of Cape Town in South  Africa, 
answers: 
Tracing the origins of viruses is difficult because they don't leave fossils  
and because of the tricks they use to make copies of themselves within the 
cells  they've invaded. Some viruses even have the ability to stitch their own 
genes  into those of the cells they infect, which means studying their ancestry 
 requires untangling it from the history of their hosts and other organisms. 
What  makes the process even more complicated is that viruses don't just 
infect  humans; they can infect basically any organism—from _bacteria_ 
(http://www.sciam.com/topic.cfm?id=bacteria)  to horses; seaweed to people. 
Still, scientists have been able to piece together some viral histories,  
based on the fact that the genes of many viruses—such as those that cause herpes  
and mono—seem to share some properties with cells' own genes. This could 
suggest  that they started as big bits of cellular DNA and then became independent—
or  that these viruses came along very early in _evolution_ 
(http://www.sciam.com/topic.cfm?id=evolution) , and some of their DNA stuck around in cells'  
genomes. The fact that some viruses that infect humans share structural 
features  with viruses that infect bacteria could mean that all of these viruses have 
a  common origin, dating back several billion years. This highlights another  
problem with tracing virus origins: most modern viruses seem to be a 
patchwork  of bits that come from different sources—a sort of "mix and match" approach 
to  building an organism. 

The fact that viruses like the deadly Ebola and Marburg viruses, as well  as 
the distantly related viruses that cause measles and rabies, are only found  
in a limited number of species suggests that those viruses are relatively  new—
after all, those organisms came along somewhat recently in evolutionary  time. 
Many of these "new" viruses likely originated in insects many million  years 
ago and at some point in evolution developed the ability to infect other  
species—probably as insects interacted with or fed from them. 

HIV, which is thought to have first emerged in humans in the 1930s, is  
another kind of virus, known as a retrovirus. These simple viruses are akin to  
elements found in normal cells that have the ability to copy and insert  
themselves throughout the genome. There are a number of viruses that have a  similar 
way of copying themselves—a process that reverses the normal flow of  
information in cells, which is where the term "retro" comes from—and their  central 
machinery for replication may be a bridge from the _original life-forms on this 
planet_ 
(http://www.sciamdigital.com/index.cfm?fa=Products.ViewIssuePreview&ARTICLEID_CHAR=6A1A42E0-16E8-4F62-A20A-233B2E760B1)  to what we know as  life 
today. In fact, we carry among our genes many "fossilized"  retroviruses—left 
over from the infection of distant ancestors—which can help us  trace our 
evolution as a species. 

Then there are the viruses whose genomes are so large that scientists  can't 
quite figure out what part of the cell they would have come from. Take,  for 
instance, the largest-ever virus so far discovered, mimivirus: its genome is  
some 50 times larger than that of HIV and is larger than that of some bacteria. 
 Some of the largest known viruses infect simple organisms such as amoebas 
and  simple marine algae. This indicates that they may have an ancient origin,  
possibly as parasitic life-forms that then adapted to the "virus lifestyle." 
In  fact, viruses may be responsible for significant episodes of evolutionary  
change, especially in more complex types of organisms. 

At the end of the day, however, despite all of their common features and  
unique abilities to copy and spread their genomes, the origins of most viruses  
may remain forever obscure.



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