Bhagavad Gita Verse 16, Chapter 3

evam pravartitam chakram naanuvartayateeha yaha |
aghaayurindriyaaraamo mogham paartha sa jeevati || 16 ||
 
In this manner, one who does not follow this system of evolution, that malicious individual who dwells in sense pleasures, wastes his life.
 
evam : in this manner
pravartitam : evolution
chakram : system
na : does not
anuvartayati : follow
iha : this
yah : one who
aghaayu : malicious
indriyaaraamah : dwells in senses
mogham : waste
paartha : O Paartha
sah : that one
jeevati : lives
 
In the two preceding shlokas, Shri Krishna illustrated how several beings acting in the spirit of yajna brought forth the potential for serving each other. Now he takes the illustration one step further. He says that yajna is a "system of evolution". Which means, it is a method to move from a lower plane of existence to a higher plane of existence.
 
Darwin's theory of evolution describes how life evolved from simple single-celled organisms into plants, then into animals, then into primates, and culminated in our species, the humans. What comes next? Shri Krishna explains that humans, being the only species capable of rational analysis and thinking, have a choice: to remain at the current state and give in to their "lower nature", or evolve into a higher state of existence.
 
What is the "lower nature"? When one continually harbours selfish desires, and lives for the sake of sense pleasure, that person generates guilt, fear, anger, hatred, pride and other such emotions that strengthen the ego. Such an individual is termed "malicious" by Shri Krishna. That individual is said to have lived in vain, because he did not use the wonderful opportunity of being born as a human to access the higher nature.
 
And so, who is the individual of "higher nature"? It is the individual who has begun identifying with a higher ideal, and in doing so, has slowly eroded his ego in the selfless service of that higher ideal. A detailed description of such an individual was provided by Shri Krishna in the latter part of the second chapter in the "sthita-prajna-lakshana" or the signs of a wise individual. Karmayoga is the first step to participate in this system of evolution.