133:, which allowed early mammalian ancestors to effectively digest their generalised diet. The precursors to this, the triconodont teeth of reptiles, were adapted for gripping and slicing rather than chewing. The evolution of the hypocone and flat molars later allowed animals to adapt to a herbivorous diet as they could be used to break down tough plant matter through grinding. The evolution of this ability led to mammals being able to adapt to utilise a huge variety of food sources, and allowed early mammals to invade novel niches through the evolution of specialised herbivores, which experienced relative success during the middle
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as stochasticity or habitat, and it is possible to 'cherry pick' examples that fit the hypothesis. In addition, the retrospective identification of key innovations offers little in terms of understanding the processes and pressures that resulted in the adaptation and may identify a very complex evolutionary process as a single event. An example of this is the evolution of avian flight, which was identified as a key innovation in 1963 by
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52:. The term was first used in 1949 by Alden H. Miller who defined it as "key adjustments in the morphological and physiological mechanism which are essential to the origin of new major groups", although a broader, contemporary definition holds that "a key innovation is an evolutionary change in individual traits that is causally linked to an increased diversification rate in the resulting clade".
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to predation the canals increase the species fitness and allow them to escape being eaten, at least until the predator evolves an ability to overcome the defence. During the period of resistance the plants are less likely to become extinct and can diversify and speciate, and as such taxa with latex and resin canals are more diverse than their canal lacking sister taxa.
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canals in plants are used to deter predators by releasing a sticky secretion when punctured which can immobilise insects and some contain toxic or foul tasting substances. They have evolved independently approximately 40 times and are considered a key innovation. By increasing the plant's resistance
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As an evolutionary theory, key innovations has come under critical scrutiny due it being hard to test. Identification depends on finding a correlation between the innovation and increased diversity by comparing sister taxa, but this does not prove causality or isolate other causes of diversity such
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as they access it. These led rapid speciation within the genus as plants and their pollinators can become specialised to each other i.e. a species of pollinator exclusively feeds from a species of plant, and thus plant populations could easily become reproductively isolated from one another. In
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A key innovation may result in reproductive isolation, whereby those individuals with the innovation no longer breed with those without. This can lead to rapid speciation as the two populations separate and accumulate mutations.
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addition the shape and size of the nectar spur can evolve in response to pollinator adaptations, developing a co-evolutionary relationship. The genus
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The theory of key innovations has come under attack because it is hard to test in a scientific manner, but there is evidence to support the idea.
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that were not previously available. The phenomenon helps to explain how some taxa are much more diverse and have many more species than their
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169:, a diverse genus of flowering plant, are considered a key innovation because of this. Nectar spurs aid in pollination by making the
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Miller, Alden (November 22, 1949). "Some ecologic and morphologic considerations in the evolution of higher taxonomic categories".
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The mechanism by which a key innovation leads to taxonomic diversity is not certain but several hypotheses have been suggested:
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A key innovation may allow a species to invade a new region or niche and thus be freed from competition, allowing subsequent
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Cracraft, Joel (1990). "The origin of evolutionary novel pattern and process at different hierarchical levels".
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Hodges, S.A. Arnold, M.L. (1995). "Spurring plant diversification: are floral nectar spurs a key innovation?".
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Heard, S.B.; Hauser, D.L. (1995). "Key evolutionary innovations and their ecological mechanisms".
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A key innovation may, by increasing the fitness of individuals of the species, result in
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and success of a taxonomic group. Typically they bring new abilities that allows the
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349:Hunter, J.P. Jernvall, J. (1995).
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67:Increasing individual fitness
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203:and the enlargement and
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141:Reproductive isolation
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186:has over 50 species.
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26:adaptive breakthrough
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440:Mayr, Ernst (1963).
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34:phenotypic
184:Aquilegia
166:Aquilegia
152:Aquilegia
116:radiation
59:Mechanism
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215:See also
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102:A human
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363:Bibcode
209:sternum
207:of the
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179:pollen
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