b :  the action or an instance of forming and giving something off :  emission

c (1) :  a process of continuous change from a lower, simpler, or worse to a higher, more complex, or better state :  growth

d :  something evolved

b :  a theory that the various types of animals and plants have their origin in other preexisting types and that the distinguishable differences are due to modifications in successive generations;also :  the process described by this theory