Monkeys

Harry Harlow ran a famous experiment with rhesus monkeys, in which young ones were put in a cage with both a wire mesh "mother" that gave milk and a cloth "mother." The monkeys preferred to cling to the cloth mother monkey--except to eat. He drew conclusions, which are probably correct, about the need for comfort as well as food.

I have no documentation for the following story!

On my thesis experiment, the spokesman's wife had a friend (I repeat: third-hand story going on here) who had studied at UW during Harlow's work, and whose job involved cleaning his lab after hours. She thought the baby monkeys looked lonely, and she would take some of them out and cuddle them.

In my not-so-humble estimation, this wouldn't change the results significantly. But it is good to remember that experimenters don't always control the variables as tightly as they think they do.