Niche changes over evolutionary time are rather difficult to document, although their occurrence cannot be disputed. As new species arise from the fission of existing ones through the process of speciation, new niches come into existence.

Life on Earth almost certainly arose in aquatic environments, and early organisms were doubtless very small and simple. During the evolutionary history of life over geological time, organisms have become more and more complex and diversified and Earth has been filled with an overwhelming variety of plants and animals. Some taxonomic groups of organisms, such as dinosaurs, have gone extinct and been replaced by others.

Major breakthroughs in the body plans of organisms periodically open up new adaptive zones and allow bursts of evolution of new and diverse species, termed adaptive radiations. A major force that has lead to niche separation and diversification is interspecific competition.

Thus the first terrestrial organisms found themselves in a wide open ecological and competitive vaccum, feed from competition with aquatic organisms, and they rapidly radiated into the many available new terrestrial niches. Similarly, evolution of endothermy and aerial exploitation patterns has allowed major adaptive radiations; flight has evolved independently at least four times, in insects, reptiles, birds, and mammals.

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Often evolutionary interactions between two or more taxa have had reciprocal effects upon one another; thus the origin and radiation of flowering plants (angiosperms) in the Mesozoic presumably allowed insects to diversify widely, while species specificity of pollinating insects to diversify widely, while species specificity of pollinating insects in turn may well have allowed considerable diversification of plants. Indeed, Whittaker (1969) has suggested that organic diversity is self-augmenting.