While diversity in nationality, geographical background, age, and gender can enrich discussions and bring various perspectives, the statement that could most threaten the effectiveness of the panel is:
The panel members are all male.
This is because a lack of gender diversity can lead to a homogenous perspective, potentially overlooking important viewpoints and experiences that could be beneficial to the discussions. Diverse gender representation can enhance the panel's effectiveness by promoting a more comprehensive understanding of the issues being discussed.