Here’s a story for your entertainment.
One day, aliens arrived on earth and decided to study humans. They took a special interest in the vibrations close to the human body. They unanimously agreed that the vibrations could be distinguished from one another and clustered together to form wave equivalence classes. With their keen powers of observation, the aliens noticed that waves from one equivalence class often appeared before another class, and particular orders of these waves appeared more frequently before other orders.
There-after, the aliens formed schools to study the order of human associated wave sequences and their interaction with other wave sequences. They began to theorize about the relationships that exist between wave sequences and external variables. The aliens argued and argued and eventually spilt off into different schools.
Some alien schools contended that wave sequences were entirely determined by the things outside the scope of the human body. Others argued that the waves were produced entirely by the things within the human body. The former group started to experiment with their theory by strategically organizing the environments of humans and observing the changes that their manipulations produced in human associated waves. The later group got very weird. They started to abduct humans and do all sorts of unspeakable investigations with the inside parts of humans. The aliens are still arguing with one another and neither group has given up his/her preferred method of investigation.