Here is a story, straight out of Richard Dawkins' 'The Extended Phenotype'. Go and read about toxoplasma gondii. It is a cat parasite which also infects rats and changes the rats behaviour, making them more adventurous and more likely to get caught.
So inside the body of this parasite, there are genes which code for behaviour in another organism. It was not designed, but is a product of natural selection. The parasite just happens to change the rats behaviour and in doing so gets a survival advantage.
There is some suggestion that this organism may even effect our own behaviour. Isn't that a scary thought?Go Top