Genetic and environmental factors are thought to play a part.

It is also thought to play a role in territorial behavior.

"I'd never have thought to play them, but it's a lot of fun," he said.

It is also thought to play a role during embryogenesis.

Changes in estrogen levels are also thought to play a role.

Now genetics were once again thought to play a role in mental illness.

B56 alpha, is additionally thought to play a role in nuclear export.

Unwashed hands are thought to play a role, though how large is unknown.

Foreign fighters from outside Iraq are widely thought to play a key role in its network.