Here is a short post from the Gender Action Portal of HARVARD Kennedy School's Women and Public Policy Forum that shares findings clearly supporting the existence of collective intelligence and strongly indicating that collective intelligence is determined by group composition and dynamics.
More specifically, the post identifies that the presence and influence of women enhances a group's collective intelligence. This is because a major determiner of the level of collective intelligence within a group is the group's level of social sensitivity. Basically, social sensitivity is the ability to empathise; this is something women (on average) do better than men.
These findings emphasise the importance of ensuring women are encouraged to contribute fully to collaborative initiatives. This is something I have written about when exploring the conductor Paul MacAlindin's work with the National Youth Orchestra of Iraq:
This is how a collaborative person works: encourage, involve, appreciate and develop women
This is how a collaborative person works: form the habit of empowering the disempowered