Parasites are by definition bad for you. Some, such as malaria,
can kill. Others, like microbes known as Wolbachia that are
found in more than one-fifth of all insects, often make female
hosts less fertile. Now scientists discover parasites can evolve
surprisingly rapidly to become helpful instead of harmful. The
typically nasty Wolbachia can make females more fertile instead
of less, a study reveals. They're not doing it out of the
goodness of their non-existent hearts — they boost host
fertility to better spread themselves in nature. These findings
could shed light on how symbiotic or mutually beneficial
partnerships develop in nature, such as the pivotal relationship
widely believed to have led mitochondria to dwell in cells and
help them breathe oxygen. "Mitochondria are thought to have
evolved from a symbiotic relationship. It may be that the
Wolbachia in this case is well on the way to having a similar
relationship that will eventually develop into a dependency by
the host on the Wolbachia for survival,