Key innovation

In evolutionary biology, a key Innovation, also known as an adaptive breakthrough or key adaptation, is a novel phenotypic trait that allows subsequent radiation and success of a taxonomic group. Typically they bring new abilities that allows the taxa to rapidly diversify and invade niches that were not previously available. The phenomenon helps to explain how some taxa are much more diverse and have many more species than their sister taxa.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'. In evolutionary biology, a key Innovation, also known as an adaptive breakthrough or key adaptation, is a novel phenotypic trait that allows subsequent radiation and success of a taxonomic group. Typically they bring new abilities that allows the taxa to rapidly diversify and invade niches that were not previously available. The phenomenon helps to explain how some taxa are much more diverse and have many more species than their sister taxa.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'. 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. The mechanism by which a key innovation leads to taxonomic diversity is not certain but several hypotheses have been suggested: A key innovation may, by increasing the fitness of individuals of the species, result in extinction becoming less likely and allow the taxa to expand and speciate. Latex and resin 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 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. A key innovation may allow a species to invade a new region or niche and thus be freed from competition, allowing subsequent speciation and radiation. A classic example of this is the fourth cusp of mammalian molars, the hypocone, 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 eocene. Specialising for a plant based diet offered early herbivores sufficient resources to radiate as energy was not lost to higher trophic levels and few competitors existed at the time.