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Information about Dark Adaptation

Part of the Biology series on
Evolution
Mechanisms and processes
Adaptation
Genetic drift
Gene flow
Mutation
Natural selection
Speciation
Research and history
Evidence
History
Modern synthesis
Social effect / Objections
Evolutionary biology fields
Ecological genetics
Evolutionary development
Human evolution
Molecular evolution
Evolutionary history of life
Phylogenetics
Population genetics
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 An adaptation is a positive characteristic of an organism that has been favored by natural selection.[1] The concept is central to biology, particularly in evolutionary biology. The term adaptation is also sometimes used as a synonym for natural selection, but most biologists discourage this usage.

Overview

Organisms that are adapted to their environment are able to:
  • Obtain air, water, food and nutrients.
  • Cope with physical conditions such as temperature, light and heat.
  • Defend themselves from their natural enemies.
  • Reproduce.
  • Respond to changes around them.
Adaptations enable living organisms to cope with environmental stresses and pressures. Adaptation can be structural or behavioral. Structural adaptations are special body parts of an organism that help it to survive in its natural habitat (e.g., skin color, shape, body covering). Behavioral adaptations are special ways a particular organism behaves to survive in its natural habitat. Physiological adaptations are systems present in an organism that allow it to perform certain biochemical reactions (e.g., making venom, secreting slime, being able to keep a constant body temperature).

Adaptations are traits that have been selected for by natural selection. The underlying genetic basis for the adaptive trait did not arise as a consequence of the environment; the genetic variant pre-existed and was subsequently selected because it provided the bearer of that variant some advantage. The first experimental evidence of the pre-exisiting nature of genetic variants was provided by Joshua Lederberg and colleagues who developed fluctuation analysis, a method to show the random fluctuation of pre-exisitng genetic changes that conferred resistance to antibiotics by the bacterium Escherichia coli

While many traits have obvious adaptive purposes, it is worthwhile to point out that many traits are not adaptive, that is, there is no obvious reason scientists can divine for the presence of a certain trait. This situation is common and there are many causes: the utility of a trait is lost and hence does not now appear adaptive, the utility of a trait is unknown, the trait is a consequence of another trait that is adaptive (the Spandrel idea). This observation underscores two other important points: genetic variants arise randomly and hence traits can appear randomly and that because the environment for all living things is constantly in flux, the utility of adaptations will naturally ebb and flow.

Organisms that are not suitably adapted to their environment will either have to move out of the habitat or die out. The term die out in the context of adaptation simply means that the death rate over the entire species (population, gene pool ...) exceeds the birth rate for a long enough period for the species to disappear; due to individual phenotypic plasticity, individuals will be more or less successful. The opposite is selection which in this context means that the birth rate of those carrying the adaptive trait and the hence the underlying genetic variant exceeds over time the birth rate of those that do not carry the adaptive trait.

Adaptation vs. adaptiveness

A trait being adaptive, i.e. increasing the organism's fitness, is neither a necessary nor sufficient condition for it to be an adaptation.[2] Of course, an adaptation must have been adaptive at some point in an organism's evolutionary history, but such an organism's environment and ecological niche can change over time, leading to adaptations becoming redundant or even a hindrance (maladaptations). Such adaptations are termed vestigial.

Adaptation vs. acclimation

There is a great difference between adaptation and acclimation. Adaptation occurs over many generations; it is a gradual process caused by natural selection. Acclimatization generally occurs within a single lifetime and copes with issues that are less threatening. For example, if a human was to move to a higher altitude, respiration and physical exertion would become a problem, but after spending time in high altitude conditions one may acclimate to the pressure and function and no longer notice the change. This ability to acclimate is an adaptation, but not the acclimation itself.

A counter-adaptation is an adaptation that has evolved due to the selective pressure of another adaptation. This occurs in an evolutionary arms race, where a new adaptation giving one species an advantage is countered by the appearance and spread of a new feature that reduces the effectiveness of the first adaptation.

Theories

Enlarge picture
Jean-Baptiste Lamarck
The theory of adaptation was first put forth by Jean-Baptiste Lamarck. His theories are also referred to as the inheritance of acquired traits.

Lamarck's theory was for a time held as an alternative scientific explanation for evolutionary change observed by Darwin in the The Origin of Species. The classic giraffe analogy offers the best delineation between the two.
  • According to Darwin, more long-necked giraffes reproduce than short-necked giraffes and as such giraffes today have long necks.
  • According to Lamarck, it was giraffes stretching their necks in response to higher leaves that resulted in giraffes having long necks. (This trait being passed on to the next generation)
Although neither theory in its conception could provide a complete description of the mechanism of transmission of trait variation (i.e., particulate inheritance), many recognized Darwin's theory immediately upon publication as a more complete and empirically supported theory. Modern genetics have since established the fundamental implausibility of Lamarckian inheritance, due to the one-way nature of transcription. However, see epigenetics and Baldwinian evolution for analogous processes in modern evolutionary theory.

Although the vast majority of genetic variants arising from errors of DNA replication or recombination do not confer any advantage to an individual organism, the multitude of variation contained within the collective genomes of a species provides much material for natural selection to work upon allowing many adaptations to be manifest.

See also

References

1. ^ Sterelny, K. & Griffiths, P. E. (1999) Sex and Death: An Introduction to Philosophy of Biology p.217 University of Chicago Press. ISBN O-226-77304-3
2. ^ Sober, E. (1993) Philosophy of Biology. p.84 Boulder: Westview Press.


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Basic topics in
Biology (from Greek: βίος, bio, "life"; and λόγος, logos, "knowledge"), also referred to as the biological sciences, is the scientific study of life.
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In population genetics, genetic drift (or more precisely allelic drift) is the statistical effect that results from the influence that chance has on the survival of alleles (variants of a gene).
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In population genetics, gene flow (also known as gene migration) is the transfer of alleles of genes from one population to another.
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mutations are changes to the base pair sequence of the genetic material of an organism. Mutations can be caused by copying errors in the genetic material during cell division, by exposure to ultraviolet or ionizing radiation, chemical mutagens, or viruses, or can occur deliberately
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Natural selection is the process by which favorable traits that are heritable become more common in successive generations of a population of reproducing organisms, and unfavorable traits that are heritable become less
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Speciation is the evolutionary process by which new biological species arise. There are four modes of natural speciation, based on the extent to which speciating populations are geographically isolated from one another:
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evidence of the theory of evolution provides a wealth of information on the natural processes by which the variety of life on Earth developed.

Fossils are important for estimating when various lineages developed.
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Evolutionary thought has roots in antiquity as philosophical ideas known to the Greeks, Romans, Indians, Chinese and Muslims. Until the 18th century, however, Western biological thought was dominated by essentialism, the idea that living forms are static and unchanging in time.
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The modern evolutionary synthesis refers to a set of ideas from several biological specialities that were brought together to form a unified theory of evolution accepted by the great majority of working biologists.
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The social effects of evolutionary thought have been considerable. As the scientific explanation of life's diversity has developed, it has often displaced alternative, sometimes very widely held, explanations.
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There have been numerous objections to evolution since alternative evolutionary ideas came to be hotly debated around the start of the nineteenth century.
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Evolutionary biology is a sub-field of biology concerned with the origin and descent of species, as well as their change, multiplication, and diversity over time.
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For the book see Ecological Genetics (book)
Ecological genetics is the study of genetics in the context of the interactions among organisms and between the organisms and their environment.
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Evolutionary developmental biology (evolution of development or informally, evo-devo) is a field of biology that compares the developmental processes of different animals and plants in an attempt to determine the ancestral relationship between organisms and how
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Human evolution is the part of biological evolution concerning the emergence of humans as a distinct species from other apes. It is the subject of a broad scientific inquiry that seeks to understand and describe how this change and development occurred.
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Molecular evolution is the process of evolution at the scale of DNA, RNA, and proteins. Molecular evolution emerged as a scientific field in the 1960s as researchers from molecular biology, evolutionary biology and population genetics sought to understand recent discoveries on the
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The evolutionary history of life and the origin of life are fields of ongoing geological and biological research. Although it is not necessary to understand the origin of life on earth to accept evolution by natural
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phylogenetics (Greek: phyle = tribe, race and genetikos = relative to birth, from genesis = birth) is the study of evolutionary relatedness among various groups of organisms (e.g., species, populations).
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Population genetics is the study of the allele frequency distribution and change under the influence of the four evolutionary forces: natural selection, genetic drift, mutation and gene flow. It also takes account of population subdivision and population structure in space.
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Plantae
  • Chromalveolata
  • Heterokontophyta
  • Haptophyta
  • Cryptophyta
  • Alveolata

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    • Natural selection is the process by which favorable traits that are heritable become more common in successive generations of a population of reproducing organisms, and unfavorable traits that are heritable become less
    ..... Click the link for more information.
    Biology (from Greek: βίος, bio, "life"; and λόγος, logos, "knowledge"), also referred to as the biological sciences, is the scientific study of life.
    ..... Click the link for more information.
    Evolutionary biology is a sub-field of biology concerned with the origin and descent of species, as well as their change, multiplication, and diversity over time.
    ..... Click the link for more information.
    E. coli

    Binomial name
    Escherichia coli
    (Migula 1895)
    Castellani and Chalmers 1919

    Escherichia coli (IPA: [ˌɛ.
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    phenotypic plasticity. Such plasticity in some cases expresses as several highly morphologically distinct results; in other cases, a continuous norm of reaction describes the functional interrelationship of a range of environments to a range of phenotypes.
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    Fitness (often denoted in population genetics models) is a central concept in evolutionary theory. It describes the capability of an individual of certain genotype to reproduce, and usually is equal to the proportion of the individual's genes in all the genes of the next generation.
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    necessary and sufficient condition of another means that the former statement is true if and only if the latter is true.
    • A necessary condition of a statement must be satisfied for the statement to be true.

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    niche (pronounced nich, neesh or nish)[] is a term describing the relational position of a species or population in its ecosystem[1]. The ecological niche describes how an organism or population responds to the distribution of resources and competitors (e. g.
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    A maladaptation is an adaptation that is (or has become) less helpful than harmful. It is a term used when discussing both humans and animals in fields such as evolutionary biology, biology, psychology (where it applies to behaviors and other learned survival mechanisms) and other
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