Adaptation

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This article is about the evolutionary process. Adaptation_sentence_0

For other uses, see Adaptation (disambiguation). Adaptation_sentence_1

Not to be confused with Adoption or Acclimatization. Adaptation_sentence_2

In biology, adaptation has three related meanings. Adaptation_sentence_3

Firstly, it is the dynamic evolutionary process that fits organisms to their environment, enhancing their evolutionary fitness. Adaptation_sentence_4

Secondly, it is a state reached by the population during that process. Adaptation_sentence_5

Thirdly, it is a phenotypic trait or adaptive trait, with a functional role in each individual organism, that is maintained and has evolved through natural selection. Adaptation_sentence_6

Historically, adaptation has been described from the time of the ancient Greek philosophers such as Empedocles and Aristotle. Adaptation_sentence_7

In 18th and 19th century natural theology, adaptation was taken as evidence for the existence of a deity. Adaptation_sentence_8

Charles Darwin proposed instead that it was explained by natural selection. Adaptation_sentence_9

Adaptation is related to biological fitness, which governs the rate of evolution as measured by change in gene frequencies. Adaptation_sentence_10

Often, two or more species co-adapt and co-evolve as they develop adaptations that interlock with those of the other species, such as with flowering plants and pollinating insects. Adaptation_sentence_11

In mimicry, species evolve to resemble other species; in Müllerian mimicry this is a mutually beneficial co-evolution as each of a group of strongly defended species (such as wasps able to sting) come to advertise their defences in the same way. Adaptation_sentence_12

Features evolved for one purpose may be co-opted for a different one, as when the insulating feathers of dinosaurs were co-opted for bird flight. Adaptation_sentence_13

Adaptation is a major topic in the philosophy of biology, as it concerns function and purpose (teleology). Adaptation_sentence_14

Some biologists try to avoid terms which imply purpose in adaptation, not least because it suggests a deity's intentions, but others note that adaptation is necessarily purposeful. Adaptation_sentence_15

History Adaptation_section_0

Main article: History of evolutionary thought Adaptation_sentence_16

Adaptation is an observable fact of life accepted by philosophers and natural historians from ancient times, independently of their views on evolution, but their explanations differed. Adaptation_sentence_17

Empedocles did not believe that adaptation required a final cause (a purpose), but thought that it "came about naturally, since such things survived." Adaptation_sentence_18

Aristotle did believe in final causes, but assumed that species were fixed. Adaptation_sentence_19

In natural theology, adaptation was interpreted as the work of a deity and as evidence for the existence of God. Adaptation_sentence_20

William Paley believed that organisms were perfectly adapted to the lives they led, an argument that shadowed Gottfried Wilhelm Leibniz, who had argued that God had brought about "the best of all possible worlds." Adaptation_sentence_21

Voltaire's satire Dr. Adaptation_sentence_22 Pangloss is a parody of this optimistic idea, and David Hume also argued against design. Adaptation_sentence_23

The Bridgewater Treatises are a product of natural theology, though some of the authors managed to present their work in a fairly neutral manner. Adaptation_sentence_24

The series was lampooned by Robert Knox, who held quasi-evolutionary views, as the Bilgewater Treatises. Adaptation_sentence_25

Charles Darwin broke with the tradition by emphasising the flaws and limitations which occurred in the animal and plant worlds. Adaptation_sentence_26

Jean-Baptiste Lamarck proposed a tendency for organisms to become more complex, moving up a ladder of progress, plus "the influence of circumstances," usually expressed as use and disuse. Adaptation_sentence_27

This second, subsidiary element of his theory is what is now called Lamarckism, a proto-evolutionary hypothesis of the inheritance of acquired characteristics, intended to explain adaptations by natural means. Adaptation_sentence_28

Other natural historians, such as Buffon, accepted adaptation, and some also accepted evolution, without voicing their opinions as to the mechanism. Adaptation_sentence_29

This illustrates the real merit of Darwin and Alfred Russel Wallace, and secondary figures such as Henry Walter Bates, for putting forward a mechanism whose significance had only been glimpsed previously. Adaptation_sentence_30

A century later, experimental field studies and breeding experiments by people such as E. Adaptation_sentence_31 B. Ford and Theodosius Dobzhansky produced evidence that natural selection was not only the 'engine' behind adaptation, but was a much stronger force than had previously been thought. Adaptation_sentence_32

General principles Adaptation_section_1

What adaptation is Adaptation_section_2

Adaptation is primarily a process rather than a physical form or part of a body. Adaptation_sentence_33

An internal parasite (such as a liver fluke) can illustrate the distinction: such a parasite may have a very simple bodily structure, but nevertheless the organism is highly adapted to its specific environment. Adaptation_sentence_34

From this we see that adaptation is not just a matter of visible traits: in such parasites critical adaptations take place in the life cycle, which is often quite complex. Adaptation_sentence_35

However, as a practical term, "adaptation" often refers to a product: those features of a species which result from the process. Adaptation_sentence_36

Many aspects of an animal or plant can be correctly called adaptations, though there are always some features whose function remains in doubt. Adaptation_sentence_37

By using the term adaptation for the evolutionary process, and adaptive trait for the bodily part or function (the product), one may distinguish the two different senses of the word. Adaptation_sentence_38

Adaptation is one of the two main processes that explain the observed diversity of species, such as the different species of Darwin's finches. Adaptation_sentence_39

The other process is speciation, in which new species arise, typically through reproductive isolation. Adaptation_sentence_40

An example widely used today to study the interplay of adaptation and speciation is the evolution of cichlid fish in African lakes, where the question of reproductive isolation is complex. Adaptation_sentence_41

Adaptation is not always a simple matter where the ideal phenotype evolves for a given environment. Adaptation_sentence_42

An organism must be viable at all stages of its development and at all stages of its evolution. Adaptation_sentence_43

This places constraints on the evolution of development, behaviour, and structure of organisms. Adaptation_sentence_44

The main constraint, over which there has been much debate, is the requirement that each genetic and phenotypic change during evolution should be relatively small, because developmental systems are so complex and interlinked. Adaptation_sentence_45

However, it is not clear what "relatively small" should mean, for example polyploidy in plants is a reasonably common large genetic change. Adaptation_sentence_46

The origin of eukaryotic endosymbiosis is a more dramatic example. Adaptation_sentence_47

All adaptations help organisms survive in their ecological niches. Adaptation_sentence_48

The adaptive traits may be structural, behavioural or physiological. Adaptation_sentence_49

Structural adaptations are physical features of an organism, such as shape, body covering, armament, and internal organization. Adaptation_sentence_50

Behavioural adaptations are inherited systems of behaviour, whether inherited in detail as instincts, or as a neuropsychological capacity for learning. Adaptation_sentence_51

Examples include searching for food, mating, and vocalizations. Adaptation_sentence_52

Physiological adaptations permit the organism to perform special functions such as making venom, secreting slime, and phototropism), but also involve more general functions such as growth and development, temperature regulation, ionic balance and other aspects of homeostasis. Adaptation_sentence_53

Adaptation affects all aspects of the life of an organism. Adaptation_sentence_54

The following definitions are given by the evolutionary biologist Theodosius Dobzhansky: Adaptation_sentence_55

Adaptation_description_list_0

  • 1. Adaptation is the evolutionary process whereby an organism becomes better able to live in its habitat or habitats.Adaptation_item_0_0
  • 2. Adaptedness is the state of being adapted: the degree to which an organism is able to live and reproduce in a given set of habitats.Adaptation_item_0_1
  • 3. An adaptive trait is an aspect of the developmental pattern of the organism which enables or enhances the probability of that organism surviving and reproducing.Adaptation_item_0_2

What adaptation is not Adaptation_section_3

Adaptation differs from flexibility, acclimatization, and learning, all of which are changes during life which are not inherited. Adaptation_sentence_56

Flexibility deals with the relative capacity of an organism to maintain itself in different habitats: its degree of specialization. Adaptation_sentence_57

Acclimatization describes automatic physiological adjustments during life; learning means improvement in behavioral performance during life. Adaptation_sentence_58

Flexibility stems from phenotypic plasticity, the ability of an organism with a given genotype (genetic type) to change its phenotype (observable characteristics) in response to changes in its habitat, or to move to a different habitat. Adaptation_sentence_59

The degree of flexibility is inherited, and varies between individuals. Adaptation_sentence_60

A highly specialized animal or plant lives only in a well-defined habitat, eats a specific type of food, and cannot survive if its needs are not met. Adaptation_sentence_61

Many herbivores are like this; extreme examples are koalas which depend on Eucalyptus, and giant pandas which require bamboo. Adaptation_sentence_62

A generalist, on the other hand, eats a range of food, and can survive in many different conditions. Adaptation_sentence_63

Examples are humans, rats, crabs and many carnivores. Adaptation_sentence_64

The tendency to behave in a specialized or exploratory manner is inherited—it is an adaptation. Adaptation_sentence_65

Rather different is developmental flexibility: "An animal or plant is developmentally flexible if when it is raised in or transferred to new conditions, it changes in structure so that it is better fitted to survive in the new environment," writes evolutionary biologist John Maynard Smith. Adaptation_sentence_66

If humans move to a higher altitude, respiration and physical exertion become a problem, but after spending time in high altitude conditions they acclimatize to the reduced partial pressure of oxygen, such as by producing more red blood cells. Adaptation_sentence_67

The ability to acclimatize is an adaptation, but the acclimatization itself is not. Adaptation_sentence_68

The reproductive rate declines, but deaths from some tropical diseases also go down. Adaptation_sentence_69

Over a longer period of time, some people are better able to reproduce at high altitudes than others. Adaptation_sentence_70

They contribute more heavily to later generations, and gradually by natural selection the whole population becomes adapted to the new conditions. Adaptation_sentence_71

This has demonstrably occurred, as the observed performance of long-term communities at higher altitude is significantly better than the performance of new arrivals, even when the new arrivals have had time to acclimatize. Adaptation_sentence_72

Adaptedness and fitness Adaptation_section_4

Main articles: Fitness (biology) and Fitness landscape Adaptation_sentence_73

There is a relationship between adaptedness and the concept of fitness used in population genetics. Adaptation_sentence_74

Differences in fitness between genotypes predict the rate of evolution by natural selection. Adaptation_sentence_75

Natural selection changes the relative frequencies of alternative phenotypes, insofar as they are heritable. Adaptation_sentence_76

However, a phenotype with high adaptedness may not have high fitness. Adaptation_sentence_77

Dobzhansky mentioned the example of the Californian redwood, which is highly adapted, but a relict species in danger of extinction. Adaptation_sentence_78

Elliott Sober commented that adaptation was a retrospective concept since it implied something about the history of a trait, whereas fitness predicts a trait's future. Adaptation_sentence_79

Adaptation_description_list_1

  • 1. Relative fitness. The average contribution to the next generation by a genotype or a class of genotypes, relative to the contributions of other genotypes in the population. This is also known as Darwinian fitness, selection coefficient, and other terms.Adaptation_item_1_3
  • 2. Absolute fitness. The absolute contribution to the next generation by a genotype or a class of genotypes. Also known as the Malthusian parameter when applied to the population as a whole.Adaptation_item_1_4
  • 3. Adaptedness. The extent to which a phenotype fits its local ecological niche. Researchers can sometimes test this through a reciprocal transplant.Adaptation_item_1_5

Sewall Wright proposed that populations occupy adaptive peaks on a fitness landscape. Adaptation_sentence_80

To evolve to another, higher peak, a population would first have to pass through a valley of maladaptive intermediate stages, and might be "trapped" on a peak that is not optimally adapted. Adaptation_sentence_81

Types Adaptation_section_5

Changes in habitat Adaptation_section_6

Before Darwin, adaptation was seen as a fixed relationship between an organism and its habitat. Adaptation_sentence_82

It was not appreciated that as the climate changed, so did the habitat; and as the habitat changed, so did the biota. Adaptation_sentence_83

Also, habitats are subject to changes in their biota: for example, invasions of species from other areas. Adaptation_sentence_84

The relative numbers of species in a given habitat are always changing. Adaptation_sentence_85

Change is the rule, though much depends on the speed and degree of the change. Adaptation_sentence_86

When the habitat changes, three main things may happen to a resident population: habitat tracking, genetic change or extinction. Adaptation_sentence_87

In fact, all three things may occur in sequence. Adaptation_sentence_88

Of these three effects only genetic change brings about adaptation. Adaptation_sentence_89

When a habitat changes, the resident population typically moves to more suitable places; this is the typical response of flying insects or oceanic organisms, which have wide (though not unlimited) opportunity for movement. Adaptation_sentence_90

This common response is called habitat tracking. Adaptation_sentence_91

It is one explanation put forward for the periods of apparent stasis in the fossil record (the punctuated equilibrium theory). Adaptation_sentence_92

Genetic change Adaptation_section_7

Genetic change occurs in a population when natural selection and mutations act on its genetic variability. Adaptation_sentence_93

The first pathways of enzyme-based metabolism may have been parts of purine nucleotide metabolism, with previous metabolic pathways being part of the ancient RNA world. Adaptation_sentence_94

By this means, the population adapts genetically to its circumstances. Adaptation_sentence_95

Genetic changes may result in visible structures, or may adjust physiological activity in a way that suits the habitat. Adaptation_sentence_96

The varying shapes of the beaks of Darwin's finches, for example, are driven by differences in the ALX1 gene. Adaptation_sentence_97

Habitats and biota do frequently change. Adaptation_sentence_98

Therefore, it follows that the process of adaptation is never finally complete. Adaptation_sentence_99

Over time, it may happen that the environment changes little, and the species comes to fit its surroundings better and better. Adaptation_sentence_100

On the other hand, it may happen that changes in the environment occur relatively rapidly, and then the species becomes less and less well adapted. Adaptation_sentence_101

Seen like this, adaptation is a genetic tracking process, which goes on all the time to some extent, but especially when the population cannot or does not move to another, less hostile area. Adaptation_sentence_102

Given enough genetic change, as well as specific demographic conditions, an adaptation may be enough to bring a population back from the brink of extinction in a process called evolutionary rescue. Adaptation_sentence_103

Adaptation does affect, to some extent, every species in a particular ecosystem. Adaptation_sentence_104

Leigh Van Valen thought that even in a stable environment, competing species constantly had to adapt to maintain their relative standing. Adaptation_sentence_105

This became known as the Red Queen hypothesis, as seen in host-parasite interaction. Adaptation_sentence_106

Existing genetic variation and mutation were the traditional sources of material on which natural selection could act. Adaptation_sentence_107

In addition, horizontal gene transfer is possible between organisms in different species, using mechanisms as varied as gene cassettes, plasmids, transposons and viruses such as bacteriophages. Adaptation_sentence_108

Co-adaptation Adaptation_section_8

Main article: Co-adaptation Adaptation_sentence_109

In coevolution, where the existence of one species is tightly bound up with the life of another species, new or 'improved' adaptations which occur in one species are often followed by the appearance and spread of corresponding features in the other species. Adaptation_sentence_110

These co-adaptational relationships are intrinsically dynamic, and may continue on a trajectory for millions of years, as has occurred in the relationship between flowering plants and pollinating insects. Adaptation_sentence_111

Mimicry Adaptation_section_9

Main article: Mimicry Adaptation_sentence_112

Bates' work on Amazonian butterflies led him to develop the first scientific account of mimicry, especially the kind of mimicry which bears his name: Batesian mimicry. Adaptation_sentence_113

This is the mimicry by a palatable species of an unpalatable or noxious species (the model), gaining a selective advantage as predators avoid the model and therefore also the mimic. Adaptation_sentence_114

Mimicry is thus an anti-predator adaptation. Adaptation_sentence_115

A common example seen in temperate gardens is the hoverfly, many of which—though bearing no sting—mimic the warning coloration of hymenoptera (wasps and bees). Adaptation_sentence_116

Such mimicry does not need to be perfect to improve the survival of the palatable species. Adaptation_sentence_117

Bates, Wallace and Fritz Müller believed that Batesian and Müllerian mimicry provided evidence for the action of natural selection, a view which is now standard amongst biologists. Adaptation_sentence_118

Trade-offs Adaptation_section_10

All adaptations have a downside: horse legs are great for running on grass, but they can't scratch their backs; mammals' hair helps temperature, but offers a niche for ectoparasites; the only flying penguins do is under water. Adaptation_sentence_119

Adaptations serving different functions may be mutually destructive. Adaptation_sentence_120

Compromise and makeshift occur widely, not perfection. Adaptation_sentence_121

Selection pressures pull in different directions, and the adaptation that results is some kind of compromise. Adaptation_sentence_122

Consider the antlers of the Irish elk, (often supposed to be far too large; in deer antler size has an allometric relationship to body size). Adaptation_sentence_123

Obviously, antlers serve positively for defence against predators, and to score victories in the annual rut. Adaptation_sentence_124

But they are costly in terms of resource. Adaptation_sentence_125

Their size during the last glacial period presumably depended on the relative gain and loss of reproductive capacity in the population of elks during that time. Adaptation_sentence_126

As another example, camouflage to avoid detection is destroyed when vivid coloration is displayed at mating time. Adaptation_sentence_127

Here the risk to life is counterbalanced by the necessity for reproduction. Adaptation_sentence_128

Stream-dwelling salamanders, such as Caucasian salamander or Gold-striped salamander have very slender, long bodies, perfectly adapted to life at the banks of fast small rivers and mountain brooks. Adaptation_sentence_129

Elongated body protects their larvae from being washed out by current. Adaptation_sentence_130

However, elongated body increases risk of desiccation and decreases dispersal ability of the salamanders; it also negatively affects their fecundity. Adaptation_sentence_131

As a result, fire salamander, less perfectly adapted to the mountain brook habitats, is in general more successful, have a higher fecundity and broader geographic range. Adaptation_sentence_132

The peacock's ornamental train (grown anew in time for each mating season) is a famous adaptation. Adaptation_sentence_133

It must reduce his maneuverability and flight, and is hugely conspicuous; also, its growth costs food resources. Adaptation_sentence_134

Darwin's explanation of its advantage was in terms of sexual selection: "This depends on the advantage which certain individuals have over other individuals of the same sex and species, in exclusive relation to reproduction." Adaptation_sentence_135

The kind of sexual selection represented by the peacock is called 'mate choice,' with an implication that the process selects the more fit over the less fit, and so has survival value. Adaptation_sentence_136

The recognition of sexual selection was for a long time in abeyance, but has been rehabilitated. Adaptation_sentence_137

The conflict between the size of the human foetal brain at birth, (which cannot be larger than about 400 cm, else it will not get through the mother's pelvis) and the size needed for an adult brain (about 1400 cm), means the brain of a newborn child is quite immature. Adaptation_sentence_138

The most vital things in human life (locomotion, speech) just have to wait while the brain grows and matures. Adaptation_sentence_139

That is the result of the birth compromise. Adaptation_sentence_140

Much of the problem comes from our upright bipedal stance, without which our pelvis could be shaped more suitably for birth. Adaptation_sentence_141

Neanderthals had a similar problem. Adaptation_sentence_142

As another example, the long neck of a giraffe brings benefits but at a cost. Adaptation_sentence_143

The neck of a giraffe can be up to 2 m (6 ft 7 in) in length. Adaptation_sentence_144

The benefits are that it can be used for inter-species competition or for foraging on tall trees where shorter herbivores cannot reach. Adaptation_sentence_145

The cost is that a long neck is heavy and adds to the animal's body mass, requiring additional energy to build the neck and to carry its weight around. Adaptation_sentence_146

Shifts in function Adaptation_section_11

Pre-adaptation Adaptation_section_12

Pre-adaptation occurs when a population has characteristics which by chance are suited for a set of conditions not previously experienced. Adaptation_sentence_147

For example, the polyploid cordgrass Spartina townsendii is better adapted than either of its parent species to their own habitat of saline marsh and mud-flats. Adaptation_sentence_148

Among domestic animals, the White Leghorn chicken is markedly more resistant to vitamin B1 deficiency than other breeds; on a plentiful diet this makes no difference, but on a restricted diet this preadaptation could be decisive. Adaptation_sentence_149

Pre-adaptation may arise because a natural population carries a huge quantity of genetic variability. Adaptation_sentence_150

In diploid eukaryotes, this is a consequence of the system of sexual reproduction, where mutant alleles get partially shielded, for example, by genetic dominance. Adaptation_sentence_151

Microorganisms, with their huge populations, also carry a great deal of genetic variability. Adaptation_sentence_152

The first experimental evidence of the pre-adaptive nature of genetic variants in microorganisms was provided by Salvador Luria and Max Delbrück who developed the Fluctuation Test, a method to show the random fluctuation of pre-existing genetic changes that conferred resistance to bacteriophages in Escherichia coli. Adaptation_sentence_153

Co-option of existing traits: exaptation Adaptation_section_13

Main article: Exaptation Adaptation_sentence_154

Features that now appear as adaptations sometimes arose by co-option of existing traits, evolved for some other purpose. Adaptation_sentence_155

The classic example is the ear ossicles of mammals, which we know from paleontological and embryological evidence originated in the upper and lower jaws and the hyoid bone of their synapsid ancestors, and further back still were part of the gill arches of early fish. Adaptation_sentence_156

The word exaptation was coined to cover these common evolutionary shifts in function. Adaptation_sentence_157

The flight feathers of birds evolved from the much earlier feathers of dinosaurs, which might have been used for insulation or for display. Adaptation_sentence_158

Niche construction Adaptation_section_14

Animals including earthworms, beavers and humans use some of their adaptations to modify their surroundings, so as to maximize their chances of surviving and reproducing. Adaptation_sentence_159

Beavers create dams and lodges, changing the ecosystems of the valleys around them. Adaptation_sentence_160

Earthworms, as Darwin noted, improve the topsoil in which they live by incorporating organic matter. Adaptation_sentence_161

Humans have constructed extensive civilizations with cities in environments as varied as the Arctic and hot deserts. Adaptation_sentence_162

In all three cases, the construction and maintenance of ecological niches helps drive the continued selection of the genes of these animals, in an environment that the animals have modified. Adaptation_sentence_163

Non-adaptive traits Adaptation_section_15

Main articles: Spandrel (biology) and Vestigiality Adaptation_sentence_164

Some traits do not appear to be adaptive as they have a neutral or deleterious effect on fitness in the current environment. Adaptation_sentence_165

Because genes often have pleiotropic effects, not all traits may be functional: they may be what Stephen Jay Gould and Richard Lewontin called spandrels, features brought about by neighbouring adaptations, on the analogy with the often highly decorated triangular areas between pairs of arches in architecture, which began as functionless features. Adaptation_sentence_166

Another possibility is that a trait may have been adaptive at some point in an organism's evolutionary history, but a change in habitats caused what used to be an adaptation to become unnecessary or even maladapted. Adaptation_sentence_167

Such adaptations are termed vestigial. Adaptation_sentence_168

Many organisms have vestigial organs, which are the remnants of fully functional structures in their ancestors. Adaptation_sentence_169

As a result of changes in lifestyle the organs became redundant, and are either not functional or reduced in functionality. Adaptation_sentence_170

Since any structure represents some kind of cost to the general economy of the body, an advantage may accrue from their elimination once they are not functional. Adaptation_sentence_171

Examples: wisdom teeth in humans; the loss of pigment and functional eyes in cave fauna; the loss of structure in endoparasites. Adaptation_sentence_172

Extinction and coextinction Adaptation_section_16

Main articles: Extinction and Coextinction Adaptation_sentence_173

If a population cannot move or change sufficiently to preserve its long-term viability, then obviously, it will become extinct, at least in that locale. Adaptation_sentence_174

The species may or may not survive in other locales. Adaptation_sentence_175

Species extinction occurs when the death rate over the entire species exceeds the birth rate for a long enough period for the species to disappear. Adaptation_sentence_176

It was an observation of Van Valen that groups of species tend to have a characteristic and fairly regular rate of extinction. Adaptation_sentence_177

Just as there is co-adaptation, there is also coextinction, the loss of a species due to the extinction of another with which it is coadapted, as with the extinction of a parasitic insect following the loss of its host, or when a flowering plant loses its pollinator, or when a food chain is disrupted. Adaptation_sentence_178

Philosophical issues Adaptation_section_17

Main articles: Adaptationism and Teleology in biology Adaptation_sentence_179

Adaptation raises philosophical issues concerning how biologists speak of function and purpose, as this carries implications of evolutionary history – that a feature evolved by natural selection for a specific reason – and potentially of supernatural intervention – that features and organisms exist because of a deity's conscious intentions. Adaptation_sentence_180

In his biology, Aristotle introduced teleology to describe the adaptedness of organisms, but without accepting the supernatural intention built into Plato's thinking, which Aristotle rejected. Adaptation_sentence_181

Modern biologists continue to face the same difficulty. Adaptation_sentence_182

On the one hand, adaptation is obviously purposeful: natural selection chooses what works and eliminates what does not. Adaptation_sentence_183

On the other hand, biologists by and large reject conscious purpose in evolution. Adaptation_sentence_184

The dilemma gave rise to a famous joke by the evolutionary biologist Haldane: "Teleology is like a mistress to a biologist: he cannot live without her but he's unwilling to be seen with her in public.'" Adaptation_sentence_185

David Hull commented that Haldane's mistress "has become a lawfully wedded wife. Adaptation_sentence_186

Biologists no longer feel obligated to apologize for their use of teleological language; they flaunt it." Adaptation_sentence_187

Ernst Mayr stated that "adaptedness... is a posteriori result rather than an a priori goal-seeking", meaning that the question of whether something is an adaptation can only be determined after the event. Adaptation_sentence_188

See also Adaptation_section_18

Credits to the contents of this page go to the authors of the corresponding Wikipedia page: en.wikipedia.org/wiki/Adaptation.