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thumbnail image of amourous coupleessay: The Advantage of Sex

microscopic photo of sickle-shaped cells
In sickle cell
anemia,
abnormal
hemoglobin
deforms blood
cells to sickle
shapes.

Keeping variety in store  
Sexual species can call on a "library" of locks unavailable to asexual species. This library is defined by two terms: heterozygosity, when an organism carries two different forms of a gene, and polymorphism, when a population contains multiple forms of a gene. Both are lost when a lineage becomes inbred. What is the function of heterozygosity? In the case of sickle cell anemia, the sickle gene helps to defeat malaria. So where malaria is common, the heterozygotes (those with one normal gene and one sickle gene) are better off than the homozygotes (those with a pair of normal genes or sickle genes) who will suffer from malaria or anemia.  
 
One of the main proponents of the Red Queen hypothesis was the late W. D. Hamilton. In the late 1970s, with the help of two colleagues from the University of Michigan, Hamilton built a computer model of sex and disease, a slice of artificial life. It began with an imaginary population of 200 creatures, some sexual and some asexual. Death was random. As expected, the sexual race quickly died out. In a game between sex and "asex," asex always wins -- other things being equal. That's because asexual reproduction is easier, and it's guaranteed to pass genes on to one's offspring. sea anemone
Sea anemones
reproduce
asexually.
     
page 1 | 2 | 3 | 4 | 5 | 6 adding parasites to the mix
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