Inevolutionary biology,function is the reason some object or process occurred in a system thatevolved throughnatural selection. That reason is typically that it achieves some result, such as thatchlorophyll helps to capture the energy of sunlight inphotosynthesis. Hence, the organism that contains it is more likely to survive and reproduce, in other words the function increases the organism'sfitness. A characteristic that assists in evolution is called anadaptation; other characteristics may be non-functionalspandrels, though these in turn may later be co-opted by evolution to serve new functions.
Inbiology, function has been defined in many ways. Inphysiology, it is simply what an organ, tissue, cell or molecule does.
In thephilosophy of biology, talk of function inevitably suggests some kind ofteleological purpose, even though natural selection operates without any goal for the future. All the same,biologists often use teleological language as a shorthand for function. In contemporary philosophy of biology, there are three major accounts of function in the biological world: theories of causal role, selected effect, and goal contribution.
Inphysiology, a function is an activity or process carried out by a system in anorganism, such assensation orlocomotion in an animal.[1] Thisconcept of function as opposed toform (respectively Aristotle'sergon andmorphê[2]) was central in biological explanations inclassical antiquity. In more modern times it formed part of the 1830Cuvier–Geoffroy debate, where Cuvier argued that an animal's structure was driven by its functional needs, while Geoffroy proposed that each animal's structure was modified from a common plan.[3][4][5]
Function can be defined in a variety of ways,[6][7] including as adaptation,[8] as contributing to evolutionary fitness,[9] in animal behaviour,[10] and, as discussed below, also as some kind of causal role or goal in the philosophy of biology.[11]
A functional characteristic is known inevolutionary biology as anadaptation, and the research strategy for investigating whether a character is adaptive is known asadaptationism. Although assuming that acharacter is functional may be helpful in research, some characteristics of organisms are non-functional, formed as accidentalspandrels, side effects of neighbouring functional systems.[8]
From the point of view ofnatural selection, biological functions exist to contribute tofitness, increasing the chance that an organism will survive toreproduce.[9][12] For example, the function ofchlorophyll in a plant is to capture the energy of sunlight forphotosynthesis,[13] which contributes toevolutionary success.[14]
TheethologistNiko Tinbergen named four questions, based onAristotle'sFour Causes,[10] that a biologist could ask to help explain abehaviour, though they have been generalised to a wider scope. 1) Mechanism: What mechanismscause the animal to behave as it does? 2)Ontogeny: Whatdevelopmental mechanisms in the animal's embryology (and its youth, if itlearns) created the structures that cause the behaviour? 3) Function/adaptation: What is the evolutionary function of the behaviour? 4) Evolution: What is thephylogeny of the behaviour, or in other words, when did it first appear in the evolutionary history of the animal? The questions are interdependent, so that, for example, adaptive function is constrained by embryonic development.[15][16][17][18]
Function is not the same as purpose in theteleological sense, that is, possessing conscious mental intention to achieve a goal. In thephilosophy of biology,evolution is a blind process which has no 'goal' for the future. For example, a tree does not grow flowers for any purpose, but does so simply because it has evolved to do so. To say 'a tree growsflowers to attractpollinators' would be incorrect if the 'to' implies purpose. A function describes what somethingdoes, not what its 'purpose' is. However,teleological language is often used by biologists as a shorthand way of describing function, even though its applicability is disputed.[11]
In contemporary philosophy of biology, there are three major accounts of function in the biological world: theories of causal role,[20] selected effect,[21] and goal contribution.[22]
Causal role theories of biological function trace their origin back to a 1975 paper by Robert Cummins.[20] Cummins defines the functional role of a component of a system to be the causal effect that the component has on the larger containing system. For example, the heart has the actual causal role of pumping blood in the circulatory system; therefore, the function of the heart is to pump blood. This account has been objected to on the grounds that it is too loose a notion of function. For example, the heart also has the causal effect of producing a sound, but we would not consider producing sound to be the function of the heart.[23][24]
Selected effect theories of biological functions hold that the function of a biological trait is the function that the trait wasselected for, as argued by Ruth Millikan.[21] For example, the function of the heart is pumping blood, for that is the action for which the heart was selected for by evolution. In other words, pumping blood isthe reason that the heart has evolved. This account has been criticized for being too restrictive a notion of function. It is not always clear which behavior has contributed to the selection of a trait, as biological traits can have functions, even if they have not been selected for. Beneficialmutations are initially not selected for, but they do have functions.[25]
Goal contribution theories seek to carve a middle ground between causal role and selected effect theories, as with Boorse (1977).[22] Boorse defines the function of a biological trait to be the statistically typical causal contribution of that trait to survival and reproduction. So for example, zebra stripes were sometimes said to workby confusing predators. This role of zebra stripes would contribute to the survival and reproduction of zebras, and that is why confusing predators would be said to be the function of zebra stripes. Under this account, whether or not a particular causal role of a trait is its function depends on whether that causal role contributes to the survival and reproduction of that organism.[26]
{{cite book}}:|work= ignored (help)Photosynthesis has been instrumental in the success of life on Earth
