Konrad Lorenz, in Austria, describes from 1935 onward the phenomenon of imprinting: the process by which the young of certain bird species, during a very early critical period after birth, fix a following-attachment to the first moving object they perceive — normally the mother, but in his famous experiments, Lorenz himself. Nikolaas Tinbergen, at Leiden University (Netherlands), collaborates with Lorenz from 1937 onward and develops a rigorous methodological framework for studying animal behavior in its natural environment, distinguishing between the immediate, developmental, functional, and evolutionary causes of any behavior — the scheme that would become known as 'Tinbergen's four questions'. Karl von Frisch, in Munich, independently discovers that bees communicate the location of food sources to other bees in the hive through a coded 'dance' whose orientation and duration indicate direction and distance relative to the sun. Together the three establish ethology as a rigorous scientific discipline: the study of animal behavior under natural conditions through systematic observation, in contrast to the laboratory behaviorism dominant in American psychology of the time. Their methods and concepts — imprinting, fixed action patterns, critical period, innate versus learned behavior — become the foundation of later behavioral biology, evolutionary psychology, and human ethology.