Homoplasy, in

biology Biology is the scientific study of life and living organisms. It is a broad natural science that encompasses a wide range of fields and unifying principles that explain the structure, function, growth, History of life, origin, evolution, and ...

and

phylogenetics In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...

, is the term used to describe a

feature Feature may refer to: Computing * Feature recognition, could be a hole, pocket, or notch * Feature (computer vision), could be an edge, corner or blob * Feature (machine learning), in statistics: individual measurable properties of the phenome ...

that has been gained or lost independently in separate lineages over the course of evolution. This is different from homology, which is the term used to characterize the similarity of features that can be parsimoniously explained by

common ancestry Common descent is a concept in evolutionary biology applicable when one species is the ancestor of two or more species later in time. According to modern evolutionary biology, all living beings could be descendants of a unique ancestor commonl ...

. Homoplasy can arise from both similar selection pressures acting on adapting species, and the effects of

genetic drift Genetic drift, also known as random genetic drift, allelic drift or the Wright effect, is the change in the Allele frequency, frequency of an existing gene variant (allele) in a population due to random chance. Genetic drift may cause gene va ...

Most often, homoplasy is viewed as a similarity in morphological characters. However, homoplasy may also appear in other character types, such as similarity in the genetic sequence, life cycle types or even behavioral traits.

Etymology

The term homoplasy was first used by

Ray Lankester Sir Edwin Ray Lankester (15 May 1847 – 13 August 1929) was a British zoologist.New International Encyclopaedia. An invertebrate zoologist and evolutionary biologist, he held chairs at University College London and Oxford University. He was th ...

in 1870. The corresponding adjective is either ''homoplasic'' or ''homoplastic''. It is derived from the two

Ancient Greek Ancient Greek (, ; ) includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Greek ...

words (), meaning "similar, alike, the same", and (), meaning "to shape, to mold".

Parallelism and convergence

Parallel Parallel may refer to: Mathematics * Parallel (geometry), two lines in the Euclidean plane which never intersect * Parallel (operator), mathematical operation named after the composition of electrical resistance in parallel circuits Science a ...

and

convergent evolution Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last comm ...

lead to homoplasy when different species independently evolve or gain apparently identical features, which are different from the feature inferred to have been present in their common ancestor. When the similar features are caused by an equivalent developmental mechanism, the process is referred to as parallel evolution. The process is called convergent evolution when the similarity arises from different developmental mechanisms. These types of homoplasy may occur when different lineages live in comparable

ecological niche In ecology, a niche is the match of a species to a specific environmental condition. Three variants of ecological niche are described by It describes how an organism or population responds to the distribution of Resource (biology), resources an ...

s that require similar adaptations for an increase in fitness. An interesting example is that of the

marsupial mole Marsupial moles, the Notoryctidae family, are two species of highly specialized marsupial mammals that are found in the Australian interior. They are small burrowing marsupials that anatomically converge on fossorial placental mammals, such as ...

s (

Notoryctidae Notoryctidae are a family of marsupials comprising the marsupial moles and their fossil relatives. It is the only family in the order Notoryctemorphia. Taxonomy A fossil species in a new genus was published as ''Naraboryctes''. A new diagnosis ...

), golden moles (

Chrysochloridae Golden moles are small insectivorous burrowing mammals Endemism, endemic to Sub-Saharan Africa. They comprise the family Chrysochloridae (the only family in the suborder Chrysochloridea) and as such they are Taxonomy (biology), taxonomically dis ...

) and northern moles (

Talpidae The family (biology), family Talpidae () includes the true Mole (animal), moles (as well as the shrew moles and desmans) who are small insectivore, insectivorous mammals of the order (biology), order Eulipotyphla. Talpids are all fossorial, diggi ...

). These are mammals from different geographical regions and lineages, and have all independently evolved very similar burrowing characteristics (such as cone-shaped heads and flat frontal claws) to live in a subterranean ecological niche.

Reversion

In contrast, reversal (a.k.a. vestigialization) leads to homoplasy through the disappearance of previously gained features. This process may result from changes in the environment in which certain gained characteristics are no longer relevant, or have even become costly. This can be observed in

subterranean Subterranean(s) or The Subterranean(s) may refer to: * Subterranea (geography), underground structures, both natural and man-made Literature * ''Subterranean'' (novel), a 1998 novel by James Rollins * ''Subterranean Magazine'', an American fa ...

and cave-dwelling animals by their loss of sight, in cave-dwelling animals through their loss of pigmentation, and in both

snake Snakes are elongated limbless reptiles of the suborder Serpentes (). Cladistically squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales much like other members of the group. Many species of snakes have s ...

s and

legless lizard Legless lizard may refer to any of several groups of lizards that have independently lost limbs or reduced them to the point of being of no use in locomotion.Pough ''et al.'' 1992. Herpetology: Third Edition. Pearson Prentice Hall:Pearson Education ...

s through their loss of limbs.

Distinguishing homology from homoplasy

Homoplasy, especially the type that occurs in more closely related phylogenetic groups, can make phylogenetic analysis more challenging.

Phylogenetic tree A phylogenetic tree or phylogeny is a graphical representation which shows the evolutionary history between a set of species or taxa during a specific time.Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA. In ...

s are often selected by means of

parsimony analysis In phylogenetics and computational phylogenetics, maximum parsimony is an optimality criterion under which the phylogenetic tree that minimizes the total number of character-state changes (or minimizes the cost of differentially weighted charact ...

. These analyses can be done with phenotypic characters, as well as DNA sequences. Using parsimony analysis, the hypothesis of relationships that requires the fewest (or least costly) character state transformations is preferred over alternative hypotheses. Evaluation of these trees may become a challenge when clouded by the occurrence of homoplasy in the characters used for the analysis. The most important approach to overcoming these challenges is to increase the number of independent (non-

pleiotropic Pleiotropy () is a condition in which a single gene or genetic variant influences multiple phenotypic traits. A gene that has such multiple effects is referred to as a ''pleiotropic gene''. Mutations in pleiotropic genes can impact several trait ...

, non- linked) characteristics used in the phylogenetic analysis. Along with parsimony analysis, one could perform a likelihood analysis, where the most likely tree, given a particular model of evolution, is selected, and branch lengths are inferred. According to the cladistic interpretation, homoplasy is invoked when the distribution of a character state cannot be explained parsimoniously (without extra inferred character state transformations between the terminals and their ancestral node) on a preferred phylogenetic hypothesis - that is, the feature in question arises (or disappears) at more than one point on the tree. In the case of DNA sequences, homoplasy is very common due to the redundancy of the genetic code. An observed homoplasy may simply be the result of random nucleotide substitutions accumulating over time, and thus may not need an

adaptationist Adaptationism is a scientific perspective on evolution that focuses on accounting for the products of evolution as collections of adaptive traits, each a product of natural selection with some adaptive rationale. A formal alternative would be to ...

evolutionary explanation.

Examples and applications of homoplasy

There are numerous documented examples of homoplasy within the following taxa: * Eusiroidea (

crustaceans Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of Arthropod, arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquat ...

and

Amphipoda Amphipoda () is an order (biology), order of malacostracan crustaceans with no carapace and generally with laterally compressed bodies. Amphipods () range in size from and are mostly detritivores or scavengers. There are more than 10,700 amphip ...

) *

Urticaceae The Urticaceae are a family, the nettle family, of flowering plants. The family name comes from the genus ''Urtica''. The Urticaceae include a number of well-known and useful plants, including nettles in the genus ''Urtica'', ramie (''Boehmeria ...

Asteraceae Asteraceae () is a large family (biology), family of flowering plants that consists of over 32,000 known species in over 1,900 genera within the Order (biology), order Asterales. The number of species in Asteraceae is rivaled only by the Orchi ...

Polypodioideae Polypodioideae is a subfamily belonging to the fern family Polypodiaceae, which is a member of the suborder Polypodiineae in the Pteridophyte Phylogeny Group classification of 2016 (PPG I). Alternatively, the subfamily may be treated as the ...

(Selligueoid Ferns) *

Ants Ants are eusocial insects of the family Formicidae and, along with the related wasps and bees, belong to the order Hymenoptera. Ants evolved from vespoid wasp ancestors in the Cretaceous period. More than 13,800 of an estimated total of ...

* ''

Merluccius capensis ''Merluccius capensis'' (shallow-water Cape hake or South African hake) is a ray-finned fish in the genus '' Merluccius'', found in the south-eastern Atlantic Ocean, along the coast of South Africa. It is a long, lean fish with a large head, simi ...

'' (cape hakes) *

Tarantula Tarantulas comprise a group of large and often hairy spiders of the family Theraphosidae. , 1,100 species have been identified, with 166 genera. The term "tarantula" is usually used to describe members of the family Theraphosidae, although ...

spiders of the genus ''

Bonnetina ''Bonnetina'' is a genus of Mexican tarantulas that was first described by F. Vol in 2000. Morphology Before the era of genetics and molecular phylogeny, tarantulas were classified based on the presence or absence of physical traits and chara ...

'': nearly all morphological traits within this genus are homoplastic. Only sexual features were observed to not be homoplastic, suggesting that

sexual selection Sexual selection is a mechanism of evolution in which members of one sex mate choice, choose mates of the other sex to mating, mate with (intersexual selection), and compete with members of the same sex for access to members of the opposite sex ...

may have been a driving force in the divergence of tarantulas. * Gharials, with homoplasy between ''

Tomistoma ''Tomistoma'' is a genus of gavialid crocodilians. They are noted for their long narrow snouts used to catch fish, similar to the gharial. ''Tomistoma'' contains one extant (living) member, the false gharial (''Tomistoma schlegelii''), as well ...

'' and true crocodiles, and between ''

Thoracosaurus ''Thoracosaurus'' (chest lizard) is an extinct genus of long-snouted eusuchian which existed during the Late Cretaceous and Early Paleocene in North America and Europe. Taxonomy ''Thoracosaurus'' had traditionally been thought to be related to ...

'' and ''

Gavialis ''Gavialis'' is a genus of crocodylians that includes the living gharial ''Gavialis gangeticus'' and one known extinct species, '' Gavialis bengawanicus.'' ''G. gangeticus'' comes from the Indian Subcontinent, while ''G. bengawanicus'' is know ...

''. The occurrence of homoplasy can also be used to make predictions about evolution. Recent studies have used homoplasy to predict the possibility and the path of extraterrestrial evolution. For example, Levin et al. (2017) suggest that the development of eye-like structures is highly likely, due to its numerous, independently evolved incidences on earth.

Homoplasy vs. evolutionary contingency

In his book ''Wonderful Life'',

Stephen Jay Gould Stephen Jay Gould ( ; September 10, 1941 – May 20, 2002) was an American Paleontology, paleontologist, Evolutionary biology, evolutionary biologist, and History of science, historian of science. He was one of the most influential and widely re ...

claims that repeating the evolutionary process, from any point in time onward, would not produce the same results. The occurrence of homoplasy is viewed by some biologists as an argument against Gould's theory of evolutionary contingency. Powell & Mariscal (2015) argue that this disagreement is caused by an

equivocation In logic, equivocation ("calling two different things by the same name") is an informal fallacy resulting from the use of a particular word or expression in multiple senses within an argument. It is a type of ambiguity that stems from a phrase ...

and that both the theory of contingency and homoplastic occurrence can be true at the same time.

References

{{reflist Evolutionary biology concepts Phylogenetics