In the late 1950s (my sources disagree on exactly when the experiment started, although the majority say 1957), Harry Harlow was interested in love. No, not that kind of love, but love of the parental variety. For eons, amongst a huge variety of animals, there has been a close bond between mother and child. The young animal will usually stay with the mother for a while -- a period of time that be as little as a month (e.g. the purple martin1, a bird found throughout North America) or as much as eighteen years (take your average American human). A popular theory in Harry Harlow's time was that the young animal stays with its mother for the sake of nourishment. However, it became clear that this could not be the only reason for the parent-child bond. After all, as one source2 points out, "ducklings and baby chicks feed themselves from birth, yet they still follow their mothers about and spend a great deal of time with them." So Harlow, a researcher at the University of Wisconsin, decided to explore the issue.
Harlow used rhesus monkeys in his experiment; they are similar to humans in that they nurse and show a variety of emotions early on3. Although there were a few variations, the basic experiment went like this: The monkey was separated from its mother very soon after it was born. Harlow would then put the monkey in an environment with two artificial mommies, one made of wire mesh and one made of soft foam rubber covered in terrycloth. The wire mommy had a feeding bottle attached to it, whereas the terrycloth mommy had nothing but its soft furry self. Harlow's idea was to observe the baby monkey and see which mommy it tended to cling to. And, interestingly enough, he found that even though the wire mommy was the one providing the baby with its food supply, the little monkey clung to it only when feeding. At all other times, the baby monkey spent its time hanging onto the terrycloth mommy. And, when the feeding bottle was attached to the terrycloth mommy instead, the baby monkey did not cling to the wire mommy at all4.
The social effects
Baby monkeys do, of course, become adult monkeys; and their strange, artificially-mothered childhoods can't help but have some effect. So, in addition to seeing how little rhesus monkeys reacted to their artificial mommies, Harlow got to see how they reacted to their peers when they became big rhesus monkeys. And some of them did react strangely. The ones who had been completely isolated from real monkeys during their time with the artificial mommies were socially inept. As my intro psychology book5 puts it:
They rarely engaged in normal interaction with other monkeys later on (either cowering in fear or showing abnormally aggressive behavior), and their sexual responses were inappropriate. When female monkeys that had been deprived of early social contact were successfully mated (after considerable effort), they made poor mothers, tending to neglect or abuse their first-born infants -- although they became better mothers with their later-born children.
However, those were the most extreme cases. When the little monkeys were raised with the artificial mommies, but also allowed social contact with their peers, they developed in a much healthier manner: although they developed more slowly, they were basically normal by about a year old.
What does it all mean?
For one thing, it means that there's more to that special mother-child bond than just food. And that seems nice and gives you that warm fuzzy feeling in your tummy until you remember that the little monkeys were still drawn to one of the artificial mommies, which means that it wasn't some special animal-to-animal bond but a simple physical comfort taken in the form of a soft squishy monkey-shaped model. But take heart! Because, as we can see by observing the behavior of the grown-up artificially mothered monkeys, not having a real mommy does negatively affect them -- if you'll recall, the artificially mothered monkeys took a longer time to develop when raised with other monkeys and developed completely inappropriately when exposed only to the artificial mommies. "But wait!" you may say, "that could lead to some pretty depressing conclusions about the effects of parental neglect in humans." Well, take heart yet again: just remember that monkeys raised with their peers (as most human children are, whether neglected by their parents or not) did eventually develop fairly normally even without real mommies. In essence, Harlow's experiments did not show that personality or behavior are dependent on one specific factor, but rather suggested that they are the result of a number of factors, including characteristics of the mother and interaction with peers. Of course, there are numerous other conclusions you can draw from these experiments, but I wouldn't want to ruin the fun for you by telling you all of them. Go figure them out for yourself.
2. Atkinson, Rita L., Richard C. Atkinson, Edward E. Smith, Daryl J. Bem, and Susan Nolen-Hoeksema; Hilgard's Introduction to Psychology: thirteenth edition; Harcourt Brace: New York, 2000, pp. 90-1
5. Atkinson, et al.
For more information on Harry Harlow: