Living systems are units of interactions; they exist in an ambience. From a purely biological point of view they cannot be understood independently of that part of the ambience with which they interact: the niche; nor can the niche be defined independently of the living system that specifies it.
The traditional view of purpose says it comes from on high, from God, from the Creator. Darwin's idea of natural selection makes people uncomfortable because it reverses the direction of tradition. Whereas people used to think of meaning coming from on high and being ordained from the top down, now we have Darwin saying, "No, all of this design can happen, all of this purpose can emerge from the bottom up without any direction at all."
Every living thing is, from the cosmic perspective, incredibly lucky simply to be alive. Most, 90 percent and more, of all the organisms that have ever lived have died without viable offspring, but not a single one of your ancestors, going back to the dawn of life on Earth, suffered that normal misfortune. You spring from an unbroken line of winners...
We want to make life permanent, but in doing so we go against nature, and there lies our pain. Only the mind which is always moving, without resting places and fixed ideas, can be in tune with life and therefore joyful.
A living system, due to its circular organization, is an inductive system and functions always in a predictive manner: what happened once will occur again. Its organization, (genetic and otherwise) is conservative and repeats only that which works. For this same reason living systems are historical systems; the relevance of a given conduct or mode of behavior is always determined in the past.
It is of first-class importance that our answer to the Riddle of the Sphinx should be in step with how we conduct our civilisation, and this should in turn be in step with the actual workings of living systems.
Dixxit 
