and be less frightened of danger – which can result in the same outcome.
A parasitic protozoan called toxoplasma gondii commonly infects rodents either through raw meat or cat faeces. Once inside a rat the parasite grows to maturity without causing any harm. But it has to get back inside the cat to continue its life cycle.
So it increases the dopamine levels in the rat’s amygdala – the part of the brain that is associated with fear and the “fight or flight” responses in humans. The rat then begins to enjoy danger, takes more risks, and ends up being eaten by a cat which puts the parasite right back where it wants to be. And you thought the Alien creature was fiendish!
Now the scary part is that this parasite can also infect humans! Researchers over the last decade have noticed that there are different behavioural characteristics in populations where many people are infected with this parasite compared with those in which infection is rare.
The effects are subtle and may not be apparent to the infected person or observers but infected men tend to be more dogmatic, less trusting and less respectful of rules.
Scientists at the University of California believe that the parasitical infection may explain differences in male behaviour in different parts of the world. Kevin Lafferty, author of a paper in Proceedings of the Royal Society B (vol 273, p 2749), says; “To say that toxoplasmosis makes men more macho may be over-simplifying it, but is definitely associated with neurotic behaviour, which is related to strongly differentiated gender roles”.
So what benefit would there be for the parasite in infecting humans? Well apparently it also slows down people’s reaction times leading to an increased risk of traffic accidents according to a report in BMC Infectious Diseases (vol 9, p72).
Lafferty thinks that by impairing human reactions and alertness the parasite would have made ancient humans easier prey for big cats, thus completing its life-cycle with us on the menu rather than rats.
Source: New Scientist 27/8/2011