what I find interesting about the study is it makes no mention of the indefinable concept of love.
As humans we know that love exists between members of our species, its definitely a quantifiable mental and physical connection between individuals and family groups, sometimes resulting in irrational risk to the individual for the preservation of a loved one.
We also know that love exists in less intelligent creatures such as dogs.
I don't find it impossible that these different types of primates could develop connections between individuals that may not be explained scientifically. Male primate A may just really like spending time with female primate B, and want to hang around.
