While listening to Swami Yogatmanandaji's lecture this Tuesday, where he mentioned about Darwin's evolution theory, a thought struck me which he highlighted a few years ago in another talk. The evolution is seen at two levels - physical and mental. While the Darwinian theory mostly deals with the physical aspect, the reincarnation concept deals with the mental evolution. At the physical level, the species evolve and develop characteristics to respond to nature's challenges. These evolutionary changes in response to natural changes are imperceptible across a few generations but are conspicuous when considered over many generations. The relative pace of external natural changes and internal bodily changes due to evolution is critical for the survival of species. If the natural changes are such that their pace is faster than the rate of evolutionary changes, the species could likely become extinct, being unable to cope with the rapidly changing environment.
Now moving to the mental evolution, which although is very obvious in the life of a single person from an infant to adult, can be seen on a much larger scale in the ambit of concept of reincarnation of a soul (particularized mind devoid of body). A soul with greater need for manifestation of the inner essence of divinity needs those bodies (or external conditions) that its evolved mental make-up could use. Hence it is said that a soul transmigrates from one body to another body that is capable of having a greater field-play for the mind, ultimately to get a human birth where it can manifest the mind's powers to a maximum extent and further taking up better human bodies (or external conditions) to finally reach the goal of Self-realization.
It is interesting to note that the evolution exists at these two levels simultaneously and we are an active participant in them. As living persons now, our bodies are already preparing the genes to pass to our next generation with some small imperceptible changes to help them cope better with nature and at the same time we are also preparing our minds so as to take up a body in the next life with better capabilities for manifesting our inner essence of divinity.
It appears that there is a difference in these two evolutionary paths: at the physical level, we have no conscious role to play if we consider only the internal body changes, while at the mental level, conscious efforts could be put to maneuver ourselves towards a particular direction. Now are both these evolutions co-related? Before I attempt to answer that question, I would like to explore what is the guiding force that drives this evolution. You may call it Nature or God's design or whatever term you may like to use - after all it is only a name with no explanation whatsoever. Now these driving forces, even if assumed that they are different for each kind of evolution, would share a common trait - i.e. drive the entity that they act upon towards perfection or stability. At the physical level, this force responds to natural changes to give a temporary stability (or perfection) to the species, whereas at the mental level, the same force (or a different one if you wish to call it so) strives for perfection of mind (or stability). Since they share a common trait, there is no reason for us to assume that it is not the same force that drives both these evolutions. This driving force is what is called God's power or Shakti or Prakriti by different people.
We must, however, note that our real identity is unchanging and therefore, no evolution whatsoever really exists. These perceived evolutions are readings of the Reality through the lens of mind and sense-perceptions; and these readings are themselves meaningful only on the background of the unchanging Reality.