What would most likely decrease the genetic variation in the human population?

If crossing over occurred less often during meiosis then there would be a decrease in genetic variation 

This is true hope this

Many archeologists and anthropologists disagree with dr. thorne's view.  thorne strongly believes that what many calls "homo erectus"  was in fact  homo sapiens,  and that they migrated out of africa almost 2 million years ago and dispersed throughout europe and asia. that's way different  from what scientists have always believed about the evolution of the species.