Preadaptation
Encyclopedia
In evolutionary biology, preadaptation describes a situation where a species evolves to use a preexisting structure or trait inherited from an ancestor for a potentially unrelated function. One example of preadaptation is dinosaur
s having used feather
s for insulation and display before using them to fly, or sweat glands in mammal
s being transformed into mammary gland
s.
Another example is the hypothesis proposed by zoologist Jonathan Kingdon
that before early human
s became biped
al, they began engaging in squat feeding, i.e. turning over rocks and leaves to find insects, worms, snails and other food. Consequently, they adapted flatter feet than were necessary in their previous tree-dwelling ancestors, since that makes squatting
much easier. Flatter feet are also extremely useful for bipedal animals, so they can be described as a preadaptation to bipedalism, even though (or rather because) the adaptation had nothing to do with bipedalism originally.
Arthropod
s provide the earliest identifiable fossils of land animals, from about in the Late Silurian
, and terrestrial tracks from about appear to have been made by arthropods. Arthropods were well pre-adapted to colonize land, because their existing jointed exoskeletons provided protection against desiccation, support against gravity and a means of locomotion that was not dependent on water.
Some biologists dislike the term preadaptation' as it could imply an intentional plan
, which is contrary to the nature of evolution
. Some alternative terms that have been suggested include "co-option" and exaptation
, to avoid the implication of foresight.
Some phenomena could give the appearance of foresight, however, without actually involving it, being instead attributable to simple probability. For example, future environments (for example, hotter or drier ones), may resemble those already encountered by a population at one of its current spatial or temporal margins. This is not actual foresight, but rather the luck of having adapted to a climate which later becomes more prominent. Cryptic genetic variation
may have the most strongly deleterious mutation
s purged from it, leaving an increased chance of useful adaptations, but this represents selection
acting on current genome
s with consequences for the future, rather than foresight.
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
s having used feather
Feather
Feathers are one of the epidermal growths that form the distinctive outer covering, or plumage, on birds and some non-avian theropod dinosaurs. They are considered the most complex integumentary structures found in vertebrates, and indeed a premier example of a complex evolutionary novelty. They...
s for insulation and display before using them to fly, or sweat glands in mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s being transformed into mammary gland
Mammary gland
A mammary gland is an organ in mammals that produces milk to feed young offspring. Mammals get their name from the word "mammary". In ruminants such as cows, goats, and deer, the mammary glands are contained in their udders...
s.
Another example is the hypothesis proposed by zoologist Jonathan Kingdon
Jonathan Kingdon
Jonathan Kingdon is a science author, and Research Associate at the University of Oxford.He focuses on taxonomic illustration and evolution of the mammals of Africa. He is a contributor to The Oxford Book of Modern Science Writing....
that before early human
Human
Humans are the only living species in the Homo genus...
s became biped
Biped
Bipedalism is a form of terrestrial locomotion where an organism moves by means of its two rear limbs, or legs. An animal or machine that usually moves in a bipedal manner is known as a biped , meaning "two feet"...
al, they began engaging in squat feeding, i.e. turning over rocks and leaves to find insects, worms, snails and other food. Consequently, they adapted flatter feet than were necessary in their previous tree-dwelling ancestors, since that makes squatting
Squatting position
Squatting is a posture where the weight of the body is on the feet but the knees are bent either fully or partially . In contrast, sitting, involves taking the weight of the body, at least in part, on the buttocks against the ground or a horizontal object such as a chair seat...
much easier. Flatter feet are also extremely useful for bipedal animals, so they can be described as a preadaptation to bipedalism, even though (or rather because) the adaptation had nothing to do with bipedalism originally.
Arthropod
Arthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...
s provide the earliest identifiable fossils of land animals, from about in the Late Silurian
Silurian
The Silurian is a geologic period and system that extends from the end of the Ordovician Period, about 443.7 ± 1.5 Mya , to the beginning of the Devonian Period, about 416.0 ± 2.8 Mya . As with other geologic periods, the rock beds that define the period's start and end are well identified, but the...
, and terrestrial tracks from about appear to have been made by arthropods. Arthropods were well pre-adapted to colonize land, because their existing jointed exoskeletons provided protection against desiccation, support against gravity and a means of locomotion that was not dependent on water.
Some biologists dislike the term preadaptation' as it could imply an intentional plan
Teleology
A teleology is any philosophical account which holds that final causes exist in nature, meaning that design and purpose analogous to that found in human actions are inherent also in the rest of nature. The word comes from the Greek τέλος, telos; root: τελε-, "end, purpose...
, which is contrary to the nature of evolution
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
. Some alternative terms that have been suggested include "co-option" and exaptation
Exaptation
Exaptation, cooption, and preadaptation are related terms referring to shifts in the function of a trait during evolution. For example, a trait can evolve because it served one particular function, but subsequently it may come to serve another. Exaptations are common in both anatomy and behaviour...
, to avoid the implication of foresight.
Some phenomena could give the appearance of foresight, however, without actually involving it, being instead attributable to simple probability. For example, future environments (for example, hotter or drier ones), may resemble those already encountered by a population at one of its current spatial or temporal margins. This is not actual foresight, but rather the luck of having adapted to a climate which later becomes more prominent. Cryptic genetic variation
Genetic variation
Genetic variation, variation in alleles of genes, occurs both within and among populations. Genetic variation is important because it provides the “raw material” for natural selection. Genetic variation is brought about by mutation, a change in a chemical structure of a gene. Polyploidy is an...
may have the most strongly deleterious mutation
Mutation
In molecular biology and genetics, mutations are changes in a genomic sequence: the DNA sequence of a cell's genome or the DNA or RNA sequence of a virus. They can be defined as sudden and spontaneous changes in the cell. Mutations are caused by radiation, viruses, transposons and mutagenic...
s purged from it, leaving an increased chance of useful adaptations, but this represents selection
Natural selection
Natural selection is the nonrandom process by which biologic traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution....
acting on current genome
Genome
In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....
s with consequences for the future, rather than foresight.
See also
- AdaptationAdaptationAn adaptation in biology is a trait with a current functional role in the life history of an organism that is maintained and evolved by means of natural selection. An adaptation refers to both the current state of being adapted and to the dynamic evolutionary process that leads to the adaptation....
- EvolvabilityEvolvabilityEvolvability is defined as the capacity of a system for adaptive evolution. Evolvability is the ability of a population of organisms to not merely generate genetic diversity, but to generate adaptive genetic diversity, and thereby evolve through natural selection.In order for a biological organism...
- Evolutionary capacitanceEvolutionary capacitanceJust as electric capacitors store and release charge, by analogy evolutionary capacitance is the storage and release of variation. Living systems are robust to mutations. This means that living systems accumulate genetic variation without the variation having a phenotypic effect...
- Genetic assimilationGenetic assimilationNote: Genetic assimilation is sometimes used to describe "eventual extinction of a natural species as massive pollen flow occurs from another related species and the older crop becomes more like the new crop." This usage is unrelated to the usage below....
- CanalisationCanalisation (genetics)Canalisation is a measure of the ability of a population to produce the same phenotype regardless of variability of its environment or genotype. In other words, it means robustness. The term canalisation was coined by C. H. Waddington...