This famous photograph shows Konrad Lorenz (1952) and a gaggle of greylag goslings that were imprinted on him and followed him all over his farm. Lorenz discovered that mallard ducklings are more discriminating: they would imprint on him only if he squatted low and dragged himself around, quacking all the while, for hours on end. He was a very dedicated scientist.

TIME & LIFE PICTURES/GETTY IMAGES