According to lawrence kohlberg, the majority of children younger than age nine have a of self-interest.

i believe the answer is:   psychological  experiment

in this experiment, wilhelm wundt became the first person that implement scientific method in analyzing the pyschological phenomenon.

due to this result, wilhelm wundt also able to make psychology to be acknowledged as a separate scientific field from biology.

all you have to do is look at the pictures to find hope this is the lesson you were also hope this .