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In the book I am reading for this class, The red Queen, Sex and The Evolution of Human Nature, the author, Matt Ridley helps us understand the idea that asexual reproduction is more vunerable to losing its ability to contribute its specific genes when bad mutations are also apart of the organism.

First, we must understand Herman Muller's the "Muller ratchet", which can be explained like this:

There are ten water fleas in a tank, only one of which is entirely free of mutations; the others all ahve one or several minor defects. On average only five of the water fleas in each generation manage to breed before they are eaten by a fish. The defect-free flea has a one-in-two chance of not breeding. So does the flea with the most defects, of course, but there is a difference: Once the defect-free flea is dead, the only way for it to be re-created is for another mutation to correct the mutation in a flea with a defect- a very unlikely posibility. The one with two defect can be re-created easily by a single mutation in a water flea with one defect anywhere among its genes. In other words, the random loss of certain lines of descent will mean that the average number of defects gradually increases. Just as a ratchet turns easily one way but cannot turn back, so genetic defects inevitably accumulate. the only way to prevent the ratchet from turning is for the perfect flea to have sex and pass its defect-free genes to other fleas before it dies.

Muller's ratchet applies if you use a photocopier to make a copy of acopy of a copy of a document. With each successive copy the quality deteriorates. Only if you gaurd the unblemished original can you regenerate a clean copy. But suppose the original is stored with the copies in a file and more copies are made when there is only one left in the file. You are just as likely to send out the original as to send out a copy. Once the original is lost, the best copy you canmake is less good than it was before. But you can always make a worse copy just by copying the worst copy you have.

( Ridely, Matt 48)