Oxford scientists have discovered a type of parasite that infects rats and which, instead of hurting them directly, controls their mind making them fearless of cats and thus increasing their probability of being eaten. The same parasite lives inside half of the human population. The scientists wonder what influence it has on the human mind.

The parasite, called Toxoplasma, influences the rats because, as part of its life cycle, it needs to get into the gut of a cat. It lays out eggs that get eaten by rats and other animals which often end up eaten by cats. However, as cats don't eat dead animals, the parasite has to deliver its host alive. In order to do this it influences its host's mind by producing blood cysts inside their brains.

Researchers have found that healthy rats have the ability of detecting the smell of cat urine and carefully avoid areas depicting such traces. They are so careful and sensitive to such odors that scientists often use cat's urine to test rats' panic reactions. On the other hand, infected rodents not only that don't exhibit this negative reaction, but they are actually seeking those areas where the smell of cat's urine is prevalent. The parasite is literally controlling their mind and pushing them into the cat's jaws. This obviously doesn't benefit the rodent in any way but benefits the parasite which is seeking to get into the cat's gut.

This is a dramatic example of how a creature can exhibit a spectacular intentional behavior without even having a nervous system - and thus it's obviously not aware of its own purposes.

But scientists wonder, if this parasite does such a thing to a mouse's mind, what is its effect on humans? There is no definite answer to this question yet. However, Dr. E. Fuller Torrey from the Stanley Medical Research Institute has noticed certain connections between the presence of the Toxoplasma parasite in humans and schizophrenia. Doctors have found that schizophrenics have damaged glial cells (which surround and support neurons); taxoplasma is also associated (although the cause-and-effect relation is not definitely proven) with the presence of such damaged cells. Moreover, scientists found that infected rats which were administered certain antipsychotic drugs used to treat schizophrenia, regained their fear of urine cat. Thus, the effect of taxoplasma on humans might be to increase the probability of schizophrenia.

These parasites are not the only such mind-controlling creatures out there. For example, there are certain microscopic parasites acting on insects: Dicrocoelium dendriticum controls its ant host to stay on the tips of grass baldes thus increasing its probability of being eaten by a ruminant animal, as the parasite needs to get into the gut of such an animal to complete its life cycle. Trichastrongylidae sp., a worm that lives inside grasshoppers, drives their hosts to jump into water pools (and thus drown) because its life cycle continues in the aquatic environment. There are also some parasites specialized in controlling the minds of fish: Euhaplorchis californiensis causes its host to swim near the water surface in a shaky manner and even to jump above the surface so they could be more easily spotted and preyed upon by birds - inside which the parasite continues its life cycle.

Evolution can be quite scary sometimes!