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thumbnail image of amourous coupleessay: The Advantage of Sex
drawing of the Red Queen from Alice in Wonderland
The Red Queen
is a metaphor for
evolutionary
change.
Enter the Red Queen  
In the late 1980s the Red Queen hypothesis emerged, and it has been steadily gaining popularity. First coined by Leigh Van Valen of the University of Chicago, it refers to Lewis Carroll's Through the Looking Glass, in which the Red Queen tells Alice, "[I]t takes all the running you can do, to keep in the same place." This never-ending evolutionary cycle describes many natural interactions between hosts and disease, or between predators and prey: As species that live at each other's expense coevolve, they are engaged in a constant evolutionary struggle for a survival advantage. They need "all the running they can do" because the landscape around them is constantly changing.  
   
 

The Red Queen hypothesis for sex is simple: Sex is needed to fight disease. Diseases specialize in breaking into cells, either to eat them, as fungi and bacteria do, or, like viruses, to subvert their genetic machinery for the purpose of making new viruses. To do that they use protein molecules that bind to other molecules on cell surfaces. The arms races between parasites and their hosts are all about these binding proteins. Parasites invent new keys; hosts change the locks. For if one lock is common in one generation, the key that fits it will spread like wildfire. So you can be sure that it is the very lock not to have a few generations later. According to the Red Queen hypothesis, sexual reproduction persists because it enables host species to evolve new genetic defenses against parasites that attempt to live off them.

drawing of HIV docking onto white blood cell
Immune cells
have receptors
("locks") for
binding proteins
("keys") of viruses
such as HIV, that
allow them to
dock and
gain entry.
   
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