Social event starts off friendly. Gradually, the conversation starts turning very technical or very sci-fi, then women turned away and formed their own social group. Worse, the only woman engineer on the team spends the night sipping on her drink quietly wishing she found these topics more interesting or wishing she took more CS classes so she could appreciate the intensity of the conversation. (Note, I'm using women as an example because of the posted question. But this applies just as much to the minority race, age group, etc.)
I think it is important for the manager (or any teammate in general) to make social inclusivity their top priority in a social environment. Look around, if you see that someone in the group is not engaged, steer the group conversation towards the interests of that person. Its a hard skill do develop, but its a skill managers should be actively working to improve.