Function (biology)

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In evolutionary biology, function is the reason some object or process occurred in a system that evolved through natural selection. Function (biology)_sentence_0

That reason is typically that it achieves some result, such as that chlorophyll helps to capture the energy of sunlight in photosynthesis. Function (biology)_sentence_1

Hence, the organism that contains it is more likely to survive and reproduce, in other words the function increases the organism's fitness. Function (biology)_sentence_2

A characteristic that assists in evolution is called an adaptation; other characteristics may be non-functional spandrels, though these in turn may later be co-opted by evolution to serve new functions. Function (biology)_sentence_3

In biology, function has been defined in many ways. Function (biology)_sentence_4

In physiology, it is simply what an organ, tissue, cell or molecule does. Function (biology)_sentence_5

In the philosophy of biology, talk of function inevitably suggests some kind of teleological purpose, even though natural selection operates without any goal for the future. Function (biology)_sentence_6

All the same, biologists often use teleological language as a shorthand for function. Function (biology)_sentence_7

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. Function (biology)_sentence_8

In pre-evolutionary biology Function (biology)_section_0

Further information: Four causes and Aristotle's biology Function (biology)_sentence_9

In physiology, a function is an activity or process carried out by a system in an organism, such as sensation or locomotion in an animal. Function (biology)_sentence_10

This concept of function as opposed to form (respectively Aristotle's ergon and morphê) was central in biological explanations in classical antiquity. Function (biology)_sentence_11

In more modern times it formed part of the 1830 Cuvier–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. Function (biology)_sentence_12

In evolutionary biology Function (biology)_section_1

Function can be defined in a variety of ways, including as adaptation, as contributing to evolutionary fitness, in animal behaviour, and, as discussed below, also as some kind of causal role or goal in the philosophy of biology. Function (biology)_sentence_13

Adaptation Function (biology)_section_2

Main article: Adaptation Function (biology)_sentence_14

A functional characteristic is known in evolutionary biology as an adaptation, and the research strategy for investigating whether a character is adaptive is known as adaptationism. Function (biology)_sentence_15

Although assuming that a character is functional may be helpful in research, some characteristics of organisms are non-functional, formed as accidental spandrels, side effects of neighbouring functional systems. Function (biology)_sentence_16

Natural selection Function (biology)_section_3

Main article: Natural selection Function (biology)_sentence_17

From the point of view of natural selection, biological functions exist to contribute to fitness, increasing the chance that an organism will survive to reproduce. Function (biology)_sentence_18

For example, the function of chlorophyll in a plant is to capture the energy of sunlight for photosynthesis, which contributes to evolutionary success. Function (biology)_sentence_19

In ethology Function (biology)_section_4

Main article: Tinbergen's four questions Function (biology)_sentence_20

The ethologist Niko Tinbergen named four questions, based on Aristotle's Four Causes, that a biologist could ask to help explain a behaviour, though they have been generalised to a wider scope. Function (biology)_sentence_21

1) Mechanism: What mechanisms cause the animal to behave as it does? Function (biology)_sentence_22

2) Ontogeny: What developmental mechanisms in the animal's embryology (and its youth, if it learns) created the structures that cause the behaviour? Function (biology)_sentence_23

3) Function/adaptation: What is the evolutionary function of the behaviour? Function (biology)_sentence_24

4) Evolution: What is the phylogeny of the behaviour, or in other words, when did it first appear in the evolutionary history of the animal? Function (biology)_sentence_25

The questions are interdependent, so that, for example, adaptive function is constrained by embryonic development. Function (biology)_sentence_26

In philosophy of biology Function (biology)_section_5

Main article: Teleology in biology Function (biology)_sentence_27

Function is not the same as purpose in the teleological sense, that is, possessing conscious mental intention to achieve a goal. Function (biology)_sentence_28

In the philosophy of biology, evolution is a blind process which has no 'goal' for the future. Function (biology)_sentence_29

For example, a tree does not grow flowers for any purpose, but does so simply because it has evolved to do so. Function (biology)_sentence_30

To say 'a tree grows flowers to attract pollinators' would be incorrect if the 'to' implies purpose. Function (biology)_sentence_31

A function describes what something does, not what its 'purpose' is. Function (biology)_sentence_32

However, teleological language is often used by biologists as a shorthand way of describing function, even though its applicability is disputed. Function (biology)_sentence_33

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. Function (biology)_sentence_34

Causal role Function (biology)_section_6

Causal role theories of biological function trace their origin back to a 1975 paper by Robert Cummins. Function (biology)_sentence_35

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. Function (biology)_sentence_36

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. Function (biology)_sentence_37

This account has been objected to on the grounds that it is too loose a notion of function. Function (biology)_sentence_38

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. Function (biology)_sentence_39

Selected effect Function (biology)_section_7

Further information: Natural selection Function (biology)_sentence_40

Selected effect theories of biological functions hold that the function of a biological trait is the function that the trait was selected for, as argued by Ruth Millikan. Function (biology)_sentence_41

For example, the function of the heart is pumping blood, for that is the action for which the heart was selected for by evolution. Function (biology)_sentence_42

In other words, pumping blood is the reason that the heart has evolved. Function (biology)_sentence_43

This account has been criticized for being too restrictive a notion of function. Function (biology)_sentence_44

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. Function (biology)_sentence_45

Beneficial mutations are initially not selected for, but they do have functions. Function (biology)_sentence_46

Goal contribution Function (biology)_section_8

Goal contribution theories seek to carve a middle ground between causal role and selected effect theories, as with Boorse (1977). Function (biology)_sentence_47

Boorse defines the function of a biological trait to be the statistically typical causal contribution of that trait to survival and reproduction. Function (biology)_sentence_48

So for example, zebra stripes were sometimes said to work by confusing predators. Function (biology)_sentence_49

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. Function (biology)_sentence_50

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. Function (biology)_sentence_51

See also Function (biology)_section_9

Function (biology)_unordered_list_0


Credits to the contents of this page go to the authors of the corresponding Wikipedia page: en.wikipedia.org/wiki/Function (biology).