275. We have seen from the above that living beings at different steps in development mutually create conditions for each other's experience of life and that all beings according to their position on the ladder of evolution are presented before us as constituting certain specially indispensable factors in our existence. But when living beings in this wonderful way mutually condition each other's experience of life, it is due to the principle of perspective and to eternal evolution which is thus revealed as one of the great basic cornerstones on which rests our daily awareness of being alive; for this said evolution creates exactly the conditions necessary enabling living beings to be either sufficiently superior or inferior in order to make up worlds or substances for each other's manifestation of eternal existence.