The study found that as the twins developed their own social groups away from their family, genetics played an increasingly important part in their The led the researchers to conclude that people who are genetically more inclined to being gregarious tend to gather more friends around them, and choose people who are similar to themselves. People who are naturally more reserved tend to choose people the basis of shared interests, rather than personality the researchers believe that not everything is down to genetics Environment also plays a part. Children with parents with a wide circle of friends are more likely to have a lot of active themselves, whatever their personality suggests that spending time with a learned behavior. So, if this study is right, although we may feel we're in control when it comes to our friends, it might be that our genes are doing the choosing without us even realizing it.