lamont:
Doesn't AIDS pretty conclusively prove evolution? The virus hopped from SIV in monkeys to HIV probably around the 1950s and then spread all over the world (and it mutates incredibly rapidly even within the host carrier).
First, a quick note on when HIV was formed. The earliest confirmed infeciton dates to 1959, however computer models push that date back to the 1930's. There is anicdotal evidence of HIV infection prior to that - as early as the 1880's, but there is no way to confirm those dates. More likely, is that those eariler infections were SIV which was transfered to humans.
HIV itself evolves increadably fast - give a patient 1 anti-HIV drug, and a resistant strain of HIV will evolve within months. Give 2 anti-HIV drugs and you'll still get a resistant strain - it just takes longer. Even the infectious cycle of HIV requires evolution - when HIV first infects a patient it is nearly always what we call a R5 tropic virus. This form of the virus preferntially infect cells expressing a receptor called CCR5. Over time X4 tropic virus form, which infect cells expressing a different receptor - CXCR4 to be specific.
This change in tropism is not caused by some bit of stored genetic code. It is not caused by a change in the expression levels of viral genes. Nor is it caused by changes in the expression of genes in the patient. Rather, the change in tropism is entirely, 100%, and all-together caused by
genetic mutations in the viral Env gene.
HIV is probably one of the best examples of evolution, but for another reason. Not only is virus evolution
ALWAYS seen as part of the infectious cycle, but human evolution has been observed in response to the virus. This includes:
1) Selection for the delta-CCR5 mutation among Indian (as in India, not Native) and European populations with high levels of HIV infection (delta-CCR5 confers what we call "long-term non-progression", which is a fancy way of saying "they're either immune to HIV, or HIV disease progresses so slowly in these people we cannot detect it").
2) Selection of certain MHC and TCR haplotypes (groups of genes) which provide protection against HIV - a fact first noted among prostitutes in Kenya.
http://evolution.berkeley.edu/evolibrary/article/0_0_0/medicine_04
lamont:
The flu pandemic of 1918 (and technically all flu pandemics) are also caused by mutation and natural selection -- in that case where I believe it hopped from swine to humans.
Duck -> Swine -> Humans. Every year that same loop goes round, and round, and round. Funny thing is we use our knowledge of flu genetics and evolution to predict what the next years flu virus will look like - this is how we prepare the flu vaccines
before the flu season starts. Given this you have two things you can believe - either evolution occurs and we understand it well enough to use it to design vaccines. Or, alternatively, every flu epidemic since the creation of flu vaccines was deliberately caused by the vaccine manufacturers.
Those are the only two explanations which can explain our ability to "predict" the serology of next years flu virus, and design vaccines around it. And given that I work in the biomedical field, I can say with a great deal of confidence that it's not some massive conspiracy.
But then again, maybe
I am the conspiracy. :uptosome:
Bryan