" t. He decided to raise the next generation of baby
monkeys with two different pretend mothers. One was a wire
mother, formed out of wire mesh, while the other was a mother
made out of soft terry cloth. Harlow assumed that all things being
equal, the babies would prefer the cloth mothers, since they
would be able to cuddle with the fabric. To make the experiment
more interesting, Harlow added a slight twist to a few of the
cages. Instead of hand-feeding some babies, he put their milk bottles in the hands of the wire mothers. His question was simple:
what was more important, food or affection? Which mother
would the babies want more?
In the end, it wasn't even close. No matter which mother held
the milk, the babies always preferred the cloth mothers. The
monkeys would run over to the wire mothers and quickly sate
their hunger before immediately returning to the comforting folds
of cloth. "

― Jonah Lehrer , How We Decide