Cat Ladies and Parasites

One can invoke evolution to explain "Cat Ladies".

1. Toxoplasmosis infected female humans have an increased probability of becoming cat horders.
   
2. This increases the survival probability of infected cats.
   
3. Cats living in such conditions have an increased probability of getting infected.
   
4. This increases the the survival probability of the parasite.
   

Such a positive feedback loop can drive evolution (co-evolution).

PsySci Toxoplasmosis links:

http://loom.corante.com/archives/2006/01/17/the_return_of_the_puppet_masters.php
http://www.slate.com/id/2123006/?nav=ais
http://gojomo.blogspot.com/2005/07/cat-ladies-caused-by-toxoplasmosis.html