Phenotypic disparity, also known as morphological diversity, morphological variety, morphological disparity, morphodisparity or simply disparity, refers to the variation of observable characteristics within biological groups. It was originally proposed in

paleontology Paleontology, also spelled as palaeontology or palæontology, is the scientific study of the life of the past, mainly but not exclusively through the study of fossils. Paleontologists use fossils as a means to classify organisms, measure ge ...

, and has also been introduced into the study of extant organisms. Some biologists view phenotypic disparity as an important aspect of biodiversity, while others believe that they are two different concepts.

History

Biologists' interest in phenotypic disparity predates the formal concept.

Douglas Erwin Douglas Hamilton Erwin (born 1958) is a paleobiologist, Curator of Paleozoic Invertebrates at the Smithsonian National Museum of Natural History and Chair of the Faculty at the Santa Fe Institute. He is a member of the Editorial Board for ''Curr ...

argued that it had been central to the organismal biology since

Georges Cuvier Jean Léopold Nicolas Frédéric, baron Cuvier (23 August 1769 – 13 May 1832), known as Georges Cuvier (; ), was a French natural history, naturalist and zoology, zoologist, sometimes referred to as the "founding father of paleontology". Cuv ...

, who utilized it as a criterion for animal classification. However, prior to the development of quantitative methods for measuring disparity, the disparity recognized within the

Linnaean taxonomy Linnaean taxonomy can mean either of two related concepts: # The particular form of biological classification (taxonomy) set up by Carl Linnaeus, as set forth in his ''Systema Naturae'' (1735) and subsequent works. In the taxonomy of Linnaeus th ...

faced criticism for being unnatural. This concept was first proposed in the 1980s, utilized to explore the evolutionary patterns of variation in anatomy, function, and ecology. It arose from the efforts by paleobiologists to define the evolutionary origins of the

body plan A body plan, (), or ground plan is a set of morphology (biology), morphological phenotypic trait, features common to many members of a phylum of animals. The vertebrates share one body plan, while invertebrates have many. This term, usually app ...

s of animals and by

comparative The degrees of comparison of adjectives and adverbs are the various forms taken by adjectives and adverbs when used to compare two entities (comparative degree), three or more entities (superlative degree), or when not comparing entities (positi ...

developmental Development of the human body is the process of growth to maturity. The process begins with fertilization, where an egg released from the ovary of a female is penetrated by a sperm cell from a male. The resulting zygote develops through mitosis ...

biologists to offer causal explanations for the emergence of these body plans. In 1989,

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 ...

published '' Wonderful Life'', in which he used the fossils from the

Middle Cambrian Middle or The Middle may refer to: * Centre (geometry), the point equally distant from the outer limits. Places * Middle (sheading), a subdivision of the Isle of Man * Middle Bay (disambiguation) * Middle Brook (disambiguation) * Middle Creek (di ...

Burgess Shale The Burgess Shale is a fossil-bearing deposit exposed in the Canadian Rockies of British Columbia, Canada. It is famous for the exceptional preservation of the soft parts of its fossils. At old (middle Cambrian), it is one of the earliest fos ...

to contend that the ancient

arthropods Arthropods ( ) are invertebrates in the phylum Arthropoda. They possess an arthropod exoskeleton, exoskeleton with a cuticle made of chitin, often Mineralization (biology), mineralised with calcium carbonate, a body with differentiated (Metam ...

at this site has a greater phenotypic disparity than all living arthropods. This concept has been introduced into the study of extant organisms. Initially, phenotypic disparity was considered a sub-concept of biodiversity, referred to as "morphological diversity", subsequently it acquired its own name "disparity", also known as "phenotypic disparity", "morphological disparity", "morphological variety" or "morphodisparity".

Summary

In the narrower sense, the currently widely accepted concept of

biodiversity Biodiversity is the variability of life, life on Earth. It can be measured on various levels. There is for example genetic variability, species diversity, ecosystem diversity and Phylogenetics, phylogenetic diversity. Diversity is not distribut ...

meant only the

taxonomic 280px, Generalized scheme of taxonomy Taxonomy is a practice and science concerned with classification or categorization. Typically, there are two parts to it: the development of an underlying scheme of classes (a taxonomy) and the allocation ...

diversity, or the species richness. However, some groups have a large number of species, while all of them are very similar in morphology; other groups have very few species, while they are highly heterogeneous. For example, there are nearly twice as many species of

bird Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves (), characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard-shelled eggs, a high Metabolism, metabolic rate, a fou ...

s as there are of

mammal A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...

s, indicating greater species richness, but birds are more consistent in morphology,

reproductive biology Reproductive biology includes both sexual and asexual reproduction. Reproductive biology includes a wide number of fields: * Reproductive systems * Endocrinology * Sexual development (Puberty) * Sexual maturity * Reproduction * Fertility H ...

, and

developmental biology Developmental biology is the study of the process by which animals and plants grow and develop. Developmental biology also encompasses the biology of Regeneration (biology), regeneration, asexual reproduction, metamorphosis, and the growth and di ...

. The range of their

s is relatively narrow, with outliers like

ratite Ratites () are a polyphyletic group consisting of all birds within the infraclass Palaeognathae that lack keels and cannot fly. They are mostly large, long-necked, and long-legged, the exception being the kiwi, which is also the only nocturnal ...

s (e.g. ostriches) and

penguin Penguins are a group of aquatic flightless birds from the family Spheniscidae () of the order Sphenisciformes (). They live almost exclusively in the Southern Hemisphere. Only one species, the Galápagos penguin, is equatorial, with a sm ...

s, while mammals include such diverse forms as

ape Apes (collectively Hominoidea ) are a superfamily of Old World simians native to sub-Saharan Africa and Southeast Asia (though they were more widespread in Africa, most of Asia, and Europe in prehistory, and counting humans are found global ...

armadillo Armadillos () are New World placental mammals in the order (biology), order Cingulata. They form part of the superorder Xenarthra, along with the anteaters and sloths. 21 extant species of armadillo have been described, some of which are dis ...

bat Bats are flying mammals of the order Chiroptera (). With their forelimbs adapted as wings, they are the only mammals capable of true and sustained flight. Bats are more agile in flight than most birds, flying with their very long spread-out ...

giraffe The giraffe is a large Fauna of Africa, African even-toed ungulate, hoofed mammal belonging to the genus ''Giraffa.'' It is the Largest mammals#Even-toed Ungulates (Artiodactyla), tallest living terrestrial animal and the largest ruminant on ...

marsupial Marsupials are a diverse group of mammals belonging to the infraclass Marsupialia. They are natively found in Australasia, Wallacea, and the Americas. One of marsupials' unique features is their reproductive strategy: the young are born in a r ...

s, moles, the

platypus The platypus (''Ornithorhynchus anatinus''), sometimes referred to as the duck-billed platypus, is a semiaquatic, egg-laying mammal endemic to eastern Australia, including Tasmania. The platypus is the sole living representative or monotypi ...

and

whale Whales are a widely distributed and diverse group of fully Aquatic animal, aquatic placental mammal, placental marine mammals. As an informal and Colloquialism, colloquial grouping, they correspond to large members of the infraorder Cetacea ...

s. Therefore, relying only on species richness to represent biodiversity is less comprehensive. The disparity is defined as the

phenotypic In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology (physical form and structure), its developmental processes, its biochemical and physiological propert ...

differentiation within groups. "Groups" usually refers to the taxonomic groups, including species or higher taxa. Some biologists believe that the concept of disparity should also be applied to other groups, including sexes, ages, biomorphs and the castes of

social insects Eusociality (Greek 'good' and social) is the highest level of organization of sociality. It is defined by the following characteristics: cooperative brood care (including care of offspring from other individuals), overlapping generations with ...

. Disparity has changed at different rates and independently of species richness in the

evolutionary history The history of life on Earth traces the processes by which living and extinct organisms evolved, from the earliest emergence of life to the present day. Earth formed about 4.5 billion years ago (abbreviated as ''Ga'', for '' gigaannum'') and ...

. There are two main patterns in how disparity develops over time. Some groups have developed high disparity early on in their evolution (called "early-disparity"), while others take longer to reach their maximum disparity (called "later-disparity"). The early-disparity boom may happen because species quickly explore new

habitat In ecology, habitat refers to the array of resources, biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species' habitat can be seen as the physical manifestation of its ...

s or take advantage of new

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. On the other hand, later-disparity groups may have developed new morphological forms slowly, resulting in a delay in reaching their maximum disparity.

Measuring disparity

Initially, there was no consensus on how to measure disparity. In the 1980s, taxonomic metrics was an early approach of measuring disparity among groups. It involved counting how many different

families Family (from ) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictability, structure, and safety as ...

genera Genus (; : genera ) is a taxonomic rank above species and below family as used in the biological classification of living and fossil organisms as well as viruses. In binomial nomenclature, the genus name forms the first part of the binomial s ...

there were to measuring the diversity and disparity of a taxon. It was based on the assumption that higher-ranked taxa could represent specific morphological innovations. Although this approach was criticized as it relied on artificial and non-

monophyletic In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent co ...

taxa, it provided valuable insights into the evolution of disparity. Some conclusions have been confirmed by subsequent quantitative metrics. Currently, disparity is usually quantified using the morphospace, which is a multidimensional space covering the morphological variation within a taxon. Due to the use of different mathematical tools, morphospaces may have different geometric structures and mathematical meanings. The initial step involves selecting multiple phenotypic descriptors (characteristics described in appropriate ways) that vary among different taxa. All phenotypic characteristics can be used to evaluate the disparity of a group, but the morphological characteristics are mostly used, because they are more accessible than others. Secondly, use the selected descriptors to construct a morphospace. Then, use standard

statistical dispersion In statistics, dispersion (also called variability, scatter, or spread) is the extent to which a distribution is stretched or squeezed. Common examples of measures of statistical dispersion are the variance, standard deviation, and interquartil ...

indicators, such as total range or total variance, to describe the dispersion and distribution of groups in morphospace. The morphospace is a multidimensional space, which is almost impossible to visualize, so the dimensionality of the morphospace should be reduced using

principal component analysis Principal component analysis (PCA) is a linear dimensionality reduction technique with applications in exploratory data analysis, visualization and data preprocessing. The data is linearly transformed onto a new coordinate system such that th ...

, principal coordinate analysis, nonmetric multidimensional scaling, or other mathematical methods. Therefore, it could be projected onto a two-dimensional space to visualize it.

References

{{reflist, 2, refs= {{Cite journal , last1=Clark , first1=James W. , last2=Hetherington , first2=Alexander J. , last3=Morris , first3=Jennifer L. , last4=Pressel , first4=Silvia , last5=Duckett , first5=Jeffrey G. , last6=Puttick , first6=Mark N. , last7=Schneider , first7=Harald , last8=Kenrick , first8=Paul , last9=Wellman , first9=Charles H. , last10=Donoghue , first10=Philip C. J. , year=2023 , title=Evolution of phenotypic disparity in the plant kingdom , journal=Nature Plants , language=en , volume=9 , issue=10 , pages=1618–1626 , doi=10.1038/s41477-023-01513-x , pmid=37666963 , pmc=10581900 , bibcode=2023NatPl...9.1618C , issn=2055-0278 {{Cite journal , last1=Erwin , first1=Douglas H. , author1-link=Douglas Erwin , year=2007 , title=Disparity: Morphological pattern and developmental context , url=https://onlinelibrary.wiley.com/doi/10.1111/j.1475-4983.2006.00614.x , journal=Palaeontology , language=en , volume=50 , issue=1 , pages=57–73 , doi=10.1111/j.1475-4983.2006.00614.x , bibcode=2007Palgy..50...57E , issn=0031-0239 , url-access=subscription , access-date=11 May 2024 , archive-date=18 September 2023 , archive-url=https://web.archive.org/web/20230918235340/https://onlinelibrary.wiley.com/doi/10.1111/j.1475-4983.2006.00614.x , url-status=live {{Cite journal , last=Gerber , first=Sylvain , year=2017 , title=The geometry of morphospaces: lessons from the classic R aup shell coiling model , url=https://onlinelibrary.wiley.com/doi/10.1111/brv.12276 , journal=Biological Reviews , language=en , volume=92 , issue=2 , pages=1142–1155 , doi=10.1111/brv.12276 , pmid=27151556 , issn=1464-7931 , url-access=subscription , access-date=12 May 2024 , archive-date=21 March 2023 , archive-url=https://web.archive.org/web/20230321145319/https://onlinelibrary.wiley.com/doi/10.1111/brv.12276 , url-status=live {{Cite journal , last1=Guillerme , first1=Thomas , last2=Cooper , first2=Natalie , last3=Brusatte , first3=Stephen L. , last4=Davis , first4=Katie E. , last5=Jackson , first5=Andrew L. , last6=Gerber , first6=Sylvain , last7=Goswami , first7=Anjali , last8=Healy , first8=Kevin , last9=Hopkins , first9=Melanie J. , last10=Jones , first10=Marc E. H. , last11=Lloyd , first11=Graeme T. , last12=O'Reilly , first12=Joseph E. , last13=Pate , first13=Abi , last14=Puttick , first14=Mark N. , last15=Rayfield , first15=Emily J. , year=2020 , title=Disparities in the analysis of morphological disparity , journal=Biology Letters , language=en , volume=16 , issue=7 , pages=20200199 , doi=10.1098/rsbl.2020.0199 , issn=1744-9561 , pmc=7423048 , pmid=32603646 {{Citation , last1=Hopkins , first1=Melanie J. , title=Morphological Disparity , date=2017 , work=Evolutionary Developmental Biology: A Reference Guide , pages=1–12 , editor-last=Nuno de la Rosa , editor-first=Laura , url=https://doi.org/10.1007/978-3-319-33038-9_132-1 , access-date=8 May 2024 , place=Cham , publisher=Springer International Publishing , language=en , doi=10.1007/978-3-319-33038-9_132-1 , isbn=978-3-319-33038-9 , last2=Gerber , first2=Sylvain , editor2-last=Müller , editor2-first=Gerd , url-access=subscription , archive-date=13 May 2024 , archive-url=https://web.archive.org/web/20240513112859/https://link.springer.com/referenceworkentry/10.1007/978-3-319-33038-9_132-1 , url-status=live {{Cite journal , last1=López-Martínez , first1=Andrea M. , last2=Magallón , first2=Susana , last3=von Balthazar , first3=Maria , last4=Schönenberger , first4=Jürg , last5=Sauquet , first5=Hervé , last6=Chartier , first6=Marion , year=2024 , title=Angiosperm flowers reached their highest morphological diversity early in their evolutionary history , journal=New Phytologist , language=en , volume=241 , issue=3 , pages=1348–1360 , doi=10.1111/nph.19389 , issn=0028-646X , pmc=10952840 , pmid=38029781, bibcode=2024NewPh.241.1348L {{cite journal , last1=McClain , first1=Craig R. , last2=Johnson , first2=Nicholas A. , last3=Rex , first3=Michael A. , title=Morphological disparity as a biodiversity metric in lower bathyal and abyssal gastropod assemblages , journal=Evolution , volume=58 , issue=2 , year=2004 , pages=338–348, pmid=15068350 , doi=10.1111/j.0014-3820.2004.tb01649.x {{cite book , title=From assessing to conserving biodiversity: Conceptual and practical challenges , editor-first=Elena , editor-last=Casetta , editor2-first=Jorge Marques , editor2-last=da Silva , editor3-first=Davide , editor3-last=Vecchi , first=Alessandro , last=Minelli , publisher=Springer Open , location=Switzerland , year=2019 , isbn=978-3-030-10990-5 , pages=233–246 , chapter=Biodiversity, disparity and evolvability , series=History, Philosophy and Theory of the Life Sciences , volume=24 , doi=10.1007/978-3-030-10991-2_11 , chapter-url=https://link.springer.com/chapter/10.1007/978-3-030-10991-2_11 , access-date=13 May 2024 , archive-date=19 February 2024 , archive-url=https://web.archive.org/web/20240219220314/https://link.springer.com/chapter/10.1007/978-3-030-10991-2_11 , url-status=live {{Cite journal , last1=Oyston , first1=Jack W. , last2=Hughes , first2=Martin , last3=Gerber , first3=Sylvain , last4=Wills , first4=Matthew A. , year=2016 , title=Why should we investigate the morphological disparity of plant clades? , journal=Annals of Botany , language=en , volume=117 , issue=5 , pages=859–879 , doi=10.1093/aob/mcv135 , issn=0305-7364 , pmc=4845799 , pmid=26658292 {{cite journal , last1=Pavlinov , first1=Igor , title=Morphological disparity: general conceptions and basic characteristics , journal=Archive of Zoological Museum of Moscow University , volume=48 , year=2008 , pages=343–388 , issn=0134-8647 , language=ru {{Cite journal , last1=Wills , first1=Matthew A. , last2=Briggs , first2=Derek E. G. , author-link2=Derek Briggs , last3=Fortey , first3=Richard A. , author-link3=Richard Fortey , year=1994 , title=Disparity as an evolutionary index: a comparison of Cambrian and Recent arthropods , url=https://www.cambridge.org/core/journals/paleobiology/article/abs/disparity-as-an-evolutionary-index-a-comparison-of-cambrian-and-recent-arthropods/1BE7A6A87CC92593B57FA064485CE0D8 , journal=Paleobiology , language=en , volume=20 , issue=2 , pages=93–130 , doi=10.1017/S009483730001263X , bibcode=1994Pbio...20...93W , issn=0094-8373 , url-access=subscription , access-date=8 May 2024 , archive-date=8 May 2024 , archive-url=https://web.archive.org/web/20240508015507/https://www.cambridge.org/core/journals/paleobiology/article/abs/disparity-as-an-evolutionary-index-a-comparison-of-cambrian-and-recent-arthropods/1BE7A6A87CC92593B57FA064485CE0D8 , url-status=live Biology theories Biodiversity Evolutionary biology concepts Paleontological concepts and hypotheses