Dollo's law
Encyclopedia
Dollo's law of irreversibility (also known as Dollo's law and Dollo's principle) is a hypothesis
proposed in 1893 by French
-born Belgian
paleontologist
Louis Dollo
which states that evolution
is not reversible. This hypothesis was first stated by Dollo in this way: "An organism
is unable to return, even partially, to a previous stage already realized in the ranks of its ancestor
s." According to this hypothesis a structure or organ
that has been lost or discarded through the process of evolution will not reappear in exactly the same form in that line of organisms. According to Richard Dawkins
, the law is "really just a statement about the statistical improbability of following exactly the same evolutionary trajectory twice (or, indeed, any particular trajectory), in either direction." Stephen Gould
viewed the idea less strictly, suggesting that "irreversibility
" forecloses certain evolutionary pathways once broad forms have emerged: "[For example], once you adopt the ordinary body plan of a reptile
, hundreds of options are forever closed, and future possibilities must unfold within the limits of inherited design."
proposed a new mechanism for this effect. It examined a hormone receptor
that had evolved from an ancestral protein
that was able to bind two hormone
s to a new protein that was specific for a single hormone. This change was produced by two amino acid
substitutions
, which prevent binding of the second hormone. However, several other changes subsequently occurred, which were selectively neutral as they did not affect hormone binding. When the authors tried to revert the protein back to its ancestral state by mutating the two "binding residues", they found the other changes had destabilised the ancestral state of the protein. They concluded that in order for this protein to evolve in reverse and regain its ability to bind two hormones, several independent neutral mutation
s would have to occur purely by chance with no selection pressure. As this is extremely unlikely, it may explain why evolution tends to run in one direction.
, and some gastropods have even lost the coiling of their shell during the evolutionary process. According to Gould's interpretation of Dollo's law, it would not be possible to re-gain a coiled shell after the coiling has been lost. Nevertheless, a few genera in the family Calyptraeidae
may have changed their developmental timing (heterochrony
) and gained back (re-evolution
) a coiled shell from an uncoiled limpet-like shell. Other exceptions to this law include the wings of stick insects, the larval stages of salamander
s, lost toes in lizards, and clavicle
s in non-avian theropod dinosaur
s.
Also, a recent study on the evolution of the mandibular teeth of the frog Gastrotheca guentheri
proposed its teeth have re-evolved using genetic structures already present, instead of re-evolving a whole new tooth blueprint.
Dr. John Wiens, who teaches in the Department of Ecology and Evolution at Stony Brook University, N.Y., studied the jaws of modern tree frogs for several years and compared them to fossils and DNA of over 170 amphibian species. He found that Gastrotheca guentheri, a species of tree frog native to Colombia and Ecuador, grew back teeth that had been “evolved away” millions of years ago.
The evolution of the peppered moth
over the past 250 years also gives one pause when considering Dollo's Law.
Hypothesis
A hypothesis is a proposed explanation for a phenomenon. The term derives from the Greek, ὑποτιθέναι – hypotithenai meaning "to put under" or "to suppose". For a hypothesis to be put forward as a scientific hypothesis, the scientific method requires that one can test it...
proposed in 1893 by French
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
-born Belgian
Belgium
Belgium , officially the Kingdom of Belgium, is a federal state in Western Europe. It is a founding member of the European Union and hosts the EU's headquarters, and those of several other major international organisations such as NATO.Belgium is also a member of, or affiliated to, many...
paleontologist
Paleontology
Paleontology "old, ancient", ὄν, ὀντ- "being, creature", and λόγος "speech, thought") is the study of prehistoric life. It includes the study of fossils to determine organisms' evolution and interactions with each other and their environments...
Louis Dollo
Louis Dollo
Louis Antoine Marie Joseph Dollo was a French-born Belgian palaeontologist, known for formulating Dollo's law. He graduated as an engineer at École Centrale de Lille in France. In 1878, he supervised the excavation of the famous, multiple Iguanodon find, at Bernissart, Belgium. Recently, the...
which states that 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...
is not reversible. This hypothesis was first stated by Dollo in this way: "An organism
Organism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...
is unable to return, even partially, to a previous stage already realized in the ranks of its ancestor
Ancestor
An ancestor is a parent or the parent of an ancestor ....
s." According to this hypothesis a structure or organ
Organ (anatomy)
In biology, an organ is a collection of tissues joined in structural unit to serve a common function. Usually there is a main tissue and sporadic tissues . The main tissue is the one that is unique for the specific organ. For example, main tissue in the heart is the myocardium, while sporadic are...
that has been lost or discarded through the process of evolution will not reappear in exactly the same form in that line of organisms. According to Richard Dawkins
Richard Dawkins
Clinton Richard Dawkins, FRS, FRSL , known as Richard Dawkins, is a British ethologist, evolutionary biologist and author...
, the law is "really just a statement about the statistical improbability of following exactly the same evolutionary trajectory twice (or, indeed, any particular trajectory), in either direction." Stephen Gould
Stephen Gould
Stephen Gould is an American heldentenor, born in Virginia.Having started in musical theatre, in 2006 he performed the title-role of Siegfried in Wagner's Der Ring des Nibelungen at Bayreuth...
viewed the idea less strictly, suggesting that "irreversibility
Irreversibility
In science, a process that is not reversible is called irreversible. This concept arises most frequently in thermodynamics, as applied to processes....
" forecloses certain evolutionary pathways once broad forms have emerged: "[For example], once you adopt the ordinary body plan of a reptile
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...
, hundreds of options are forever closed, and future possibilities must unfold within the limits of inherited design."
Proposed mechanism
A recent study on the evolution of protein structureProtein structure
Proteins are an important class of biological macromolecules present in all organisms. Proteins are polymers of amino acids. Classified by their physical size, proteins are nanoparticles . Each protein polymer – also known as a polypeptide – consists of a sequence formed from 20 possible L-α-amino...
proposed a new mechanism for this effect. It examined a hormone receptor
Hormone receptor
A hormone receptor is a receptor protein on the surface of a cell or in its interior that binds to a specific hormone. The hormone causes many changes to take place in the cell....
that had evolved from an ancestral protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
that was able to bind two hormone
Hormone
A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...
s to a new protein that was specific for a single hormone. This change was produced by two amino acid
Amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...
substitutions
Point mutation
A point mutation, or single base substitution, is a type of mutation that causes the replacement of a single base nucleotide with another nucleotide of the genetic material, DNA or RNA. Often the term point mutation also includes insertions or deletions of a single base pair...
, which prevent binding of the second hormone. However, several other changes subsequently occurred, which were selectively neutral as they did not affect hormone binding. When the authors tried to revert the protein back to its ancestral state by mutating the two "binding residues", they found the other changes had destabilised the ancestral state of the protein. They concluded that in order for this protein to evolve in reverse and regain its ability to bind two hormones, several independent neutral 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 would have to occur purely by chance with no selection pressure. As this is extremely unlikely, it may explain why evolution tends to run in one direction.
Proposed exceptions to Dollo's law
It is readily observed that many taxa of gastropods have reduced shellsGastropod shell
The gastropod shell is a shell which is part of the body of a gastropod or snail, one kind of mollusc. The gastropod shell is an external skeleton or exoskeleton, which serves not only for muscle attachment, but also for protection from predators and from mechanical damage...
, and some gastropods have even lost the coiling of their shell during the evolutionary process. According to Gould's interpretation of Dollo's law, it would not be possible to re-gain a coiled shell after the coiling has been lost. Nevertheless, a few genera in the family Calyptraeidae
Calyptraeidae
Calyptraeidae, common name the slipper snails or slipper limpets, cup-and-saucer snails, and Chinese hat snails are a family of small to medium-sized marine prosobranch gastropods...
may have changed their developmental timing (heterochrony
Heterochrony
In biology, heterochrony is defined as a developmental change in the timing of events, leading to changes in size and shape. There are two main components, namely the onset and offset of a particular process, and the rate at which the process operates...
) and gained back (re-evolution
Re-Evolution
Re-Evolution is a webcomic series by Gus Higuera and Juan Felipe Salcedo published on DC Comics' Zuda Comics site. The strip placed second in the monthly Zuda competition in April 2008. In July 2008 the strip was invited back to compete in the first annual Zuda Invitational, winning first place...
) a coiled shell from an uncoiled limpet-like shell. Other exceptions to this law include the wings of stick insects, the larval stages of salamander
Salamander
Salamander is a common name of approximately 500 species of amphibians. They are typically characterized by a superficially lizard-like appearance, with their slender bodies, short noses, and long tails. All known fossils and extinct species fall under the order Caudata, while sometimes the extant...
s, lost toes in lizards, and clavicle
Clavicle
In human anatomy, the clavicle or collar bone is a long bone of short length that serves as a strut between the scapula and the sternum. It is the only long bone in body that lies horizontally...
s in non-avian theropod dinosaur
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.
Also, a recent study on the evolution of the mandibular teeth of the frog Gastrotheca guentheri
Gastrotheca guentheri
Guenther's Marsupial Frog is a species of frog in the Hemiphractidae family.It is found in Colombia and Ecuador. Its natural habitats are subtropical or tropical moist lowland forests, subtropical or tropical moist montanes, and rivers. It is threatened by habitat loss.It is the only known frog...
proposed its teeth have re-evolved using genetic structures already present, instead of re-evolving a whole new tooth blueprint.
Dr. John Wiens, who teaches in the Department of Ecology and Evolution at Stony Brook University, N.Y., studied the jaws of modern tree frogs for several years and compared them to fossils and DNA of over 170 amphibian species. He found that Gastrotheca guentheri, a species of tree frog native to Colombia and Ecuador, grew back teeth that had been “evolved away” millions of years ago.
The evolution of the peppered moth
Peppered moth evolution
The evolution of the peppered moth over the last two hundred years has been studied in detail. Originally, the vast majority of peppered moths had light colouration, which effectively camouflaged them against the light-coloured trees and lichens which they rested upon...
over the past 250 years also gives one pause when considering Dollo's Law.
See also
- Entropy and lifeEntropy and lifeResearch concerning the relationship between the thermodynamic quantity entropy and the evolution of life began in around the turn of the 20th century...
- IrreversibilityIrreversibilityIn science, a process that is not reversible is called irreversible. This concept arises most frequently in thermodynamics, as applied to processes....
- Fitness landscapeFitness landscapeIn evolutionary biology, fitness landscapes or adaptive landscapes are used to visualize the relationship between genotypes and reproductive success. It is assumed that every genotype has a well-defined replication rate . This fitness is the "height" of the landscape...
- Devolution (biological fallacy)