Diversity and sustainability

For many years botanists were puzzled by the presence of certain nonessential chemical substances found within many forms of plant life. These chemicals had no apparent role within the primary production system of the plants; that is, they had no clear link to the organism's growth, maintenance or regeneration. They were termed ‘secondary metabolites’ to distinguish them from the other, primary productive substances. These secondary substances were a puzzle because it was unclear why they would persist: how could an organism expend some portion of its limited energy on the generation of such chemicals if they played no role in the plant's primary production? Surely other, competing organisms would evolve without such secondaries and supplant them by virtue of relative fitness. Plant communities, nevertheless, clearly do produce many chemical substances that play no direct role in the furtherance of their primary productivity.

The solution to this puzzle was found by broadening the scope of enquiry beyond the narrow focus on primary productivity. Evolution generally rewards the ‘relative fitness’ of an organism: its capacity to outperform its competitors within the system. One means of achieving relative fitness is the attainment of characteristics which generate individual primary productivity. These are characteristics which perform the fundamental functions of plant life (e.g. photosynthesis, seed production) most efficiently.