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Not to be confused with Adoption or Acclimatization.


General principles[edit]


Julian Huxley[1]






The following definitions are mainly due to Theodosius Dobzhansky.


Adaptedness and fitness[edit]

Main article: Fitness (biology)


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.[20]p552 This is also known as Darwinian fitness, selective coefficient, and other terms.

Brief history[edit]


  • Empedocles did not believe that adaptation required a final cause (~ purpose), but "came about naturally, since such things survived". Aristotle, however, did believe in final causes.
  • In natural theology, adaptation was interpreted as the work of a deity, even as evidence for the existence of God.[22] William Paley believed that organisms were perfectly adapted to the lives they lead, an argument that shadowed Leibniz, who had argued that God had brought about the best of all possible worlds. Voltaire's Dr Pangloss[23] is a parody of this optimistic idea, and Hume also argued against design.[24] The Bridgewater Treatises are a product of natural theology, though some of the authors managed to present their work in a fairly neutral manner. The series was lampooned by Robert Knox, who held quasi-evolutionary views, as the Bilgewater Treatises. Darwin broke with the tradition by emphasising the flaws and limitations which occurred in the animal and plant worlds.[25]
  • Lamarck's is a proto-evolutionary theory of the inheritance of acquired traits, whose main purpose is to explain adaptations by natural means.[26] He 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. His evolutionary ideas, and those of Geoffroy, fail because they cannot be reconciled with heredity. This was known even before Mendel by medical men interested in human races (Wells, Lawrence), and especially by Weismann.

Many other students of natural history, such as Buffon, accepted adaptation, and some also accepted evolution, without voicing their opinions as to the mechanism. This illustrates the real merit of Darwin and Wallace, and secondary figures such as Bates, for putting forward a mechanism whose significance had only been glimpsed previously. A century later, experimental field studies and breeding experiments by people such as Ford and Dobzhansky produced evidence that natural selection was not only the 'engine' behind adaptation, but was a much stronger force than had previously been thought.[27][28][29]

Types of adaptations[edit]

"Adaptation is the heart and soul of evolution." -Niles Eldredge[30]

Changes in habitat[edit]



Habitat tracking[edit]


Genetic change[edit]




Intimate relationships: co-adaptations[edit]

Main article: Co-adaptation


Pollinator constancy: these honeybees selectively visit flowers from only one species, as can be seen by the colour of the pollen in their baskets:



Main article: Mimicry


Bates, Wallace and Müller believed that Batesian and Müllerian mimicry provided evidence for the action of natural selection, a view which is now standard amongst biologists.[41] All aspects of this situation can be, and have been, the subject of research.[42] Field and experimental work on these ideas continues to this day; the topic connects strongly to speciation, genetics and development.[43]

The basic machinery: internal adaptations[edit]


Compromise and conflict between adaptations[edit]

"It is a profound truth that Nature does not know best; that genetical evolution... is a story of waste, makeshift, compromise and blunder." -Peter Medawar.[45]



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). Obviously antlers serve positively for defence against predators, and to score victories in the annual rut. But they are costly in terms of resource. 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.[48] Another example: camouflage to avoid detection is destroyed when vivid colors are displayed at mating time. Here the risk to life is counterbalanced by the necessity for reproduction.


An Indian peacock's train
in full display

The peacock's ornamental train (grown anew in time for each mating season) is a famous adaptation. It must reduce his maneuverability and flight, and is hugely conspicuous; also, its growth costs food resources. Darwin's explanation of its advantage was in terms of sexual selection: "it depends on the advantage which certain individuals have over other individuals of the same sex and species, in exclusive relation to reproduction".[50] 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.[51] The recognition of sexual selection was for a long time in abeyance, but has been rehabilitated.[52] In practice, the blue peafowl Pavo cristatus is a pretty successful species, with a big natural range in India, so the overall outcome of their mating system is quite viable.

The conflict between the size of the human foetal brain at birth, (which cannot be larger than about 400ccs, else it will not get through the mother's pelvis) and the size needed for an adult brain (about 1400ccs), means the brain of a newborn child is quite immature. The most vital things in human life (locomotion, speech) just have to wait while the brain grows and matures. That is the result of the birth compromise. Much of the problem comes from our upright bipedal stance, without which our pelvis could be shaped more suitably for birth. Neanderthals had a similar problem.[53][54][55]

As another example, the long neck of a giraffe is a burden and a blessing. The necks of giraffe can be over eight feet long. This neck can be used for inter-species competition or for foraging on tall trees where shorter herbivores cannot reach. However, as previously stated, there is always a trade-off. This long neck is heavy and it adds to the body mass of a giraffe, so the giraffe needs an abundance of nutrition to provide for this costly adaptation. [56]

Shifts in function[edit]

Adaptation and function are two aspects of one problem. Julian Huxley[57]


This occurs when a species or population has characteristics which (by chance) are suited for conditions which have not yet arisen. For example, the polyploid rice-grass Spartina townsendii is better adapted than either of its parent species to their own habitat of saline marsh and mud-flats.[58] White Leghorn fowl are markedly more resistant to vitamin B deficiency than other breeds.[59] On a plentiful diet there is no difference, but on a restricted diet this preadaptation could be decisive.

Pre-adaptation may occur because a natural population carries a huge quantity of genetic variability.[60] In diploid eukaryotes, this is a consequence of the system of sexual reproduction, where mutant alleles get partially shielded, for example, by the selective advantage of heterozygotes. Micro-organisms, with their huge populations, also carry a great deal of genetic variability.

The first experimental evidence of the pre-adaptive nature of genetic variants in micro-organisms was provided by Salvador Luria and Max Delbrück who developed fluctuation analysis, a method to show the random fluctuation of pre-existing genetic changes that conferred resistance to phage in the bacterium Escherichia coli.

Co-option of existing traits: exaptation[edit]

Main article: Exaptation

The classic example is the ear ossicles of mammals, which we know from palaeontological and embryological studies originated in the upper and lower jaws and the hyoid of their Synapsid ancestors, and further back still were part of the gill arches of early fish.[61][62] We owe this esoteric knowledge to the comparative anatomists, who, a century ago, were at the cutting edge of evolutionary studies.[63] The word exaptation was coined to cover these shifts in function, which are surprisingly common in evolutionary history.[64] The origin of wings from feathers that were originally used for temperature regulation is a more recent discovery (see feathered dinosaurs).

Related issues[edit]

Non-adaptive traits[edit]


Vestigial organs[edit]

Main article: Vestigiality


Fitness landscapes[edit]

Main article: Fitness landscape



Main article: Extinction



Main article: Co-extinction

Just as we have co-adaptation, there is also co-extinction. Co-extinction refers to the loss of a species due to the extinction of another; for example, the extinction of parasitic insects following the loss of their hosts. Co-extinction can also occur when a flowering plant loses its pollinator, or through the disruption of a food chain.[68] "Species co-extinction is a manifestation of the interconnectedness of organisms in complex ecosystems ... While co-extinction may not be the most important cause of species extinctions, it is certainly an insidious one".[69]

Flexibility, acclimatization, learning[edit]






Rather different is developmental flexibility: "An animal or plant is developmentally flexible if when it is raised or transferred to new conditions it develops so that it is better fitted to survive in the new circumstances".[72] Once again, there are huge differences between species, and the capacities to be flexible are inherited.


Main article: Acclimatization

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 pressure by increasing production of red blood corpuscles. The ability to acclimatize is an adaptation, but not the acclimatization itself. Fecundity goes down, but deaths from some tropical diseases also goes down.





Function and teleonomy[edit]






Main article: Teleonomy


Teleonomy: The hypothesis that adaptations arise without the existence of a prior purpose, but by the action of natural selection on genetic variability.[77]

The term may have been suggested by Colin Pittendrigh in 1958;[78] it grew out of cybernetics and self-organising systems. Ernst Mayr, George C. Williams and Jacques Monod picked up the term and used it in evolutionary biology.[79][80][81][82]

Philosophers of science have also commented on the term. Ernest Nagel analysed the concept of goal-directedness in biology;[83] and David Hull commented on the use of teleology and teleonomy by biologists:

Haldane can be found remarking, "Teleology is like a mistress to a biologist: he cannot live without her but he’s unwilling to be seen with her in public". Today the mistress has become a lawfully wedded wife. Biologists no longer feel obligated to apologize for their use of teleological language; they flaunt it. The only concession which they make to its disreputable past is to rename it ‘teleonomy’.[84]

See also[edit]


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  2. ^ Mayr, Ernst (1982). The growth of biological thought: diversity, evolution, and inheritance (1st ed.). Cambridge, Mass: Belknap Press. p. 483. ISBN 0-674-36445-7. Adaptation... could no longer be considered a static condition, a product of a creative past, and became instead a continuing dynamic process. 
  3. ^ Price P.W. 1980. The evolutionary biology of parasites. Princeton.
  5. ^ Bowler, P.J. (2003) [1984]. Evolution: the history of an idea (3rd ed.). University of California Press. p. 10. ISBN 0-520-23693-9. 
  6. ^ Patterson C. 1999. Evolution. Natural History Museum, London. p1
  7. ^ Williams, George C (1966). Adaptation and natural selection: a critique of some current evolutionary thought. Princeton University Press. p. 5. ISBN 0-691-02357-3. Evolutionary adaptation is a phenomenon of pervasive importance in biology 
  8. ^ Mayr, Ernst (1963). Animal species and evolution (1st ed.). Cambridge: Belknap Press of Harvard University Press. ISBN 0-674-03750-2. 
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