The article discusses how scientists estimated the sampling variance of co-heritability, which is a measure of how traits are passed down through generations. They used genetic analyses to develop formulas for this variance and explored the relationship between co-heritability and genetic correlation. Co-heritability combines aspects of heritability and genetic correlation, with heritability being a special case of co-heritability. Using co-heritability to describe the relationship between traits can result in smaller errors compared to using genetic correlation.