Survival of the fittest

At the most fundamental level the success of an organism can be assessed by whether it passes its genes (DNA sequences) on to the next generation. Any genetic changes - and the resultant novel proteins and enzymes - that increase the likelihood of successful reproduction are positive evolutionary events, while genetic alterations that reduce the likelihood of successful reproduction probably move the organism one step closer to extinction. 

The ultimate physical consequences of such changes (mutations) may include better means of defence or escape from predators, greater success in mating, or better response to climate change or food restrictions. For most of the lower organisms, eg bacteria and fungi, however, it is the production of natural products that enhances their chances of survival and reproductive success.