From Explores Web:
A 20-year study has found a surprising reason why some gray wolves become the pack leader. Wolves infected with the parasite Toxoplasma gondii are far more likely to end up as the top dog.
The tiny parasites are well known to cat owners, where they are a common problem. Because T. gondii can only reproduce inside cats, its effect on other animals has been somewhat overlooked. Yet it can infect almost any warm-blooded animal.