CONVERGENT EVOLUTION LIANE GABORA
CONVERGENT EVOLUTIONLIANE GABORAContact information:Liane GaboraDepartment of PsychologyUniversity of British ColumbiaOkanagan campus, 3333 University WayKelowna BC, V1V 1V7, CANADAPh: (250) 807-9849Fax: (250) 807-8439email: /Keywords: up to 15 Keywords in alphabetical order.Analogous structures, biodiversity, coexistence, common ancestry, competition, culturalevolution, divergent evolution, ecological niche, evolutionary relay, homologous structures,homology, homoplasy, parallel evolution, re-evolutionGlossary: 5 – 10 Glossary entries, with a sentence on each to explain for a non-specialist reader.1. Analogous structures – Traits arising through convergent evolution.2. Divergent evolution – The opposite of convergent evolution; species with a common ancestorevolve different traits, perhaps increasingly occupying different ecological niches.3. Evolutionary relay – How independent species acquire similar characteristics through theirevolution in similar ecosystems at different times.4. Homologous – Having a common ancestor.5. Homoplasy – Similarity in species of different ancestry that is the result of convergentevolution.6. Parallel evolution – Two independent species evolving together at the same time in the sameecospace acquire similar traits.7. Re-evolution – The re-appearance of a trait following the loss of the genes for the trait.Synopsis: a 1-paragraph SynopsisConvergent evolution occurs when organisms that are not closely related evolve traits that aresimilar, or analogous, as an adaptive response to similar environmental pressures. The genesresponsible for the two versions of the trait may be quite different. Examples include theevolution of wings in the bat, the bird, and the pterodactyl, and the evolution of glycoproteinswith antifreeze properties by fish in the Arctic and Antarctic.Chapter text:Convergent evolution refers to the evolution in different lineages of structures that are similar oranalogous, but that cannot be attributed to the existence of a common ancestor; in other words,the fact that the structures are analogous does not reflect homology. The similarity may reside atthe phenotypic level, in which case the lineages share the overt trait but the underlying DNAsequences are different. Convergent evolution occurs when species occupy similar ecological
niches and adapting in similar ways in response to similar selective pressures. Traits that arisethrough convergent evolution are referred to as analogous structures. They are contrasted withhomologous structures, which have a common origin. The opposite of convergent evolution isdivergent evolution, whereby related species evolve different traits.Well-documented cases of convergent evolution of similar DNA sequences are notplentiful; such cases are usually restricted to a few amino acids. Convergent evolution canmislead phylogenetic inference because it mimics shared ancestry. Standard phylogeneticmethods are not equipped to differentiate between the two. When convergent evolution ismistaken for homology, this produces a phylogenetic tree that is falsely reticulate or bushy inappearance, i.e. species appear to originate from a common ancestor when in fact that is not thecase.ExamplesCamera Eye of Cephalopods and VertebratesA famous example of convergent evolution is the camera eye of cephalopods (e.g., squid andoctopus), vertebrates (e.g., mammals). Their last common ancestor had just a simplephotoreceptive spot. The final structure is remarkably similar but it was achieved throughdifferent evolutionary paths, as evidenced by one significant difference: whereas in vertebrates,the blood and nerve vessels enter from the front of the retina, in the cephalopod eye, the bloodand nerve vessels enter from the back. In other words, they are wired in the opposite direction.Wings of the Bat, Bird, and PterodactylAnother oft-cited example of convergent evolution is the wings of the bat, the bird, and thepterodactyl. The forelimbs of each of these vertebrates independently morphed over time intowings that became used for flight. As with the camera eye, similar evolutionary pressures andsimilar aerodynamic constraints on the shape, size, and movement of wings led to the evolutionof wings in birds and bats that are remarkably similar in construction. The bat wing ishomologous to human and other mammal forearms because they share an ancestral state despiteserving different functions. Insects also independently evolved wings for flight.Body PlansVery similar body plans evolved independently in two clades, the marsupial fauna of Australiaand the placental mammals of the Old World. These include the body plans of sabre-toothed catsand flying squirrels. Another example of analogous body plans is the torpedo shaped body ofsharks, dolphins, and ichthyosaurs (swimming dinosaurs).Antifreeze Glycoprotein in FishFish in both the Arctic and Antarctic have evolved glycoproteins that act like antifreeze. Theglycoproteins circulate in the blood and surround tiny ice crystals, stopping them from growing.This slightly lowers the temperature at which their body fluids would freeze. Thee twopopulations of fish split long before they evolved the antifreeze genes, and in fact the genes thatproduce the antifreeze proteins are quite different. This indicates that independent episodes ofmolecular evolution occurred, with the same functional outcome.Other Examples
Other noteworthy examples of convergent evolution include the smelling organs of the terrestrialcoconut crab and those of insects, and the shells of brachiopods and bivalve mollusks. There arealso many examples of convergent evolution in plants. These include a number of hormones inplants and fungi such as gibberellin and abscisic acid, and the independent evolution in differentspecies of plants of prickles, thorns and spines, which prevent or limit herbivory. Many differentplants have evolved flowers and nectar to attract pollinating species. Another example is the rareTasmanian Beech tree is the only true deciduous (leaf shedding) tree in Australia. Although itwas long thought to be a relative of the northern hemisphere species, DNA analysis revealed thatit arose independently and that its origins date back to the Gondwana-southern supercontinent.Distinction from Related PhenomenaRe-evolutionIn re-evolution, a trait is lost because the genes responsible for it are lost, and then they evolveagain later in the same lineage. As a result, members of a lineage at time A share a trait withmembers of that lineage at time C that is not shared with members of the lineage at anintermediate time B. Unlike convergent evolution, organisms from time A and time C that sharethe trait are closely related. It is sometimes difficult to determine whether a gene was genuinelylost, or whether it been ‘switched off’ and then re-enabled later.Evolutionary RelayEvolutionary relay refers to the evolution of similar traits in independent species that live insimilar ecosystems at different times. An example of evolutionary relay is the dorsal fins ofextinct ichthyosaurs and sharks.Parallel EvolutionParallel evolution occurs when independent species acquire similar characteristics whileevolving together at the same time in the same ecospace. An example of parallel evolution isextinct browsing-horses and paleotheres. The different between parallel and convergentevolution is the following. Consider members of two lineages that are similar with respect tosome trait. In parallel evolution, the ancestors of their respective lineages were similar withrespect to that trait. In parallel evolution, the ancestors of their respective lineages were notsimilar with respect to that trait. Thus in convergent evolution they became increasingly similarover time.Sometimes, the ancestral forms are unspecified or unknown, or the range of traitsconsidered is not clearly specified. In such cases, distinguishing between parallel and convergentevolution is not straightforward. For example, the striking similarity between placental andmarsupial forms have been considered a case of convergent evolution, because they each had along evolutionary history prior to the extinction of the dinosaurs under which to differentiate.However they have also been viewed as an example of parallel evolution starting from thecommon ancestor of all marsupials and placentals. In the end, whether a particular case isconsidered parallel or convergent may depend on how far back one looks in their ancestral lines.Convergence in Cultural EvolutionConvergent evolution also takes place in culture. All humans have similar needs, our bodiesmove in similar ways, and we have a shared sense of pleasure and displeasure, comfort and
discomfort. Our environments provide us with similar materials from which to constructartifacts, and certain materials are best suited to particular purposes. These factors constrain howelements of culture change over time. Thus, much as species that are not closely related butoccupy similar ecological niches may evolve similar traits, cultures that are not derived from thesame ancestral culture may evolve similar artifacts, sports, cooking techniques, and so forth.Because culture evolves differently from living organisms, convergent evolution presentsmore of a challenge for the classification of elements of culture than it does for the classificationof organisms. The degree of relatedness of different species can be determined not just throughexamination of their phenotypic traits, but through examination of their DNA. Thus even iforganisms share a trait, if the genes underlying that trait are different, the trait will not beconsidered evidence that they are closely related. Moreover, horizontally transmitted traits are byand large not inherited, and therefore lost from the lineage, e.g. if an organism loses its tail, itsoffspring are not born without a tail. Therefore, convergent evolution of biological lineageshappens slowly, and is relatively easy to track. Finally, because organisms must solve manyproblems (reproduction, locomotion, digestion, etc.) the probability that a species is miscategorized on the basis of any one trait (i.e. how it solves any one problem) is low. Artifacts, onthe other hand, are often constructed with a single use in mind. (Though artifacts developed foruse in one context may be used to solve other problems, e.g., a screwdriver may be used to opena can of paint). Therefore, there is greater danger of mis-categorization arising through theassumption that similarity reflects homology. Moreover, there is no cultural DNA to help usdistinguish trait similarity due to true convergence from trait similarity due to shared ancestry,and since horizontally transmitted traits are retained, culture is harder to track. Finally, there areno restrictions on ‘what can mate with what’; i.e. For these reasons, the application ofphylogenetic methods to culture can lead to a classification that assumes homology when it is notpresent, and that is therefore misleadingly reticulate or bushy in appearance.Theoretical IssuesThe degree to which the diversity of life forms reflects convergence is the subject of a popularcontroversy. In the book ‘Wonderful Life’, Stephen Jay Gould claims that if the tape of life werere-wound and played back, completely different forms of life would have evolved. However,Simon Conway Morris argued that because all life forms are acted upon by the sameenvironmental and physical constraints, and there are a finite number of effective solutions tosome challenges, they gravitate toward certain body plans that effectively solve the problems ofsurvival. Conway claims that, given enough time, even the evolution of intelligence is inevitable,citing its evolution in primates, crows, and dolphins. Thus, he claims, convergence plays acentral role in shaping the products of evolution.Scheffer and van Nes showed that self-organized clusters of look-a-likes may emergespontaneously from the coevolution of competitors. This makes intuitive sense because there aretwo alternative ways to survive together: being sufficiently different or being sufficiently similar.Their theoretical model suggests that there is a tendency for evolutionary emergence of regularlyspaced lumps of similar species along a niche axis. Their model also suggests that convergentevolution is more likely in species-saturated communities with high levels of competition.Further reading:Doolittle RF (1994). Convergent evolution: the need to be explicit. Trends in BiochemicalSciences, 19, 15–18.
Chen, L., DeVries, A. L. & Cheng, C. H. (1997). Convergent evolution of antifreezeglycoproteins in Antarctic notothenioid fish and Arctic cod. Proceedings of the NationalAcademy of Sciences USA, 94, 3817–3822.Collin, R. & Cipriani, R. (2003). Dollo's law and the re-evolution of shell coiling. Proceedings ofthe Royal Society B: Biological Sciences, 270(1533), 2551–2555.Gould, S. J. (1989). Wonderful Life: The Burgess Shale and the Nature of History. W.W. Norton& Company.Kozmik, Z.; Ruzickova, J.; Jonasova, K.; Matsumoto, Y.; Vopalensky, P.; Kozmikova, I.;Strnad, H. Kawamura, S. et al. (Jul 2008). Assembly of the cnidarian camera-type eye fromvertebrate-like components. Proceedings of the National Academy of Sciences USA,105(26), 8989–8993.Morris, S. C. (2005). Life's solution: inevitable humans in a lonely universe. Cambridge, UK:Cambridge University Press.Zhang J, Kumar S (1997). Detection of convergent and parallel evolution at the amino acidsequence level. Mol Biol Evol, 14, 527–536.[List of relevant websites of interest to the ergent rary/01/4/l 014 01.html[Biographical details – up to 200 words and a photo]Liane Gabora is a professor ofpsychology at the University ofBritish Columbia, Canada. Herwork capitalizes on her training inboth theoretical biology andcognitive science. She researchesthe mechanisms underlyingbiological and cultural evolution,with a focus on the noveltygenerating, creative processes thatdrive evolutionary change, usingboth computer models andexperiments involving humanparticipants. Her goals are (1) todevelop a comprehensivetheoretical framework for cultural evolution, and (2) by undertaking a comparative study ofbiological and cultural change, to arrive at a more comprehensive understanding of howsomething could evolve. She has over 100 published papers in academic journals, book chapters,and conference proceedings. She has given lectures worldwide and has over a million dollars inresearch grants. She was recently awarded the 2011 Berlyne Award from Division 10 of theAmerican Psychological Association for outstanding research.Figures and/or tables: please note that for any non-original figures or tables permission must beobtained from the publisher. Further information is available on the Resources tab, or on thiswebpage: rs/permissions
evolution, divergent evolution, ecological niche, evolutionary relay, homologous structures, homology, homoplasy, parallel evolution, re-evolution Glossary: 5 – 10 Glossary entries, with a sentence on each to explain for a non-specialist reader. 1. Analogous structures
DIVERGENT AND CONDITIONALLY CONVERGENT SERIES WHOSE PRODUCT IS ABSOLUTELY CONVERGENT* BY FLORIAN CAJOKI § 1. Introduction. It has been shown by Abel that, if the product : 71—« I( » V«-i M„«o) 71 0 of two conditionally convergent series : 71—0 71 — 0 is convergent, it converges to the product of their sums.
Convergent synthesis should be considered in which two or more fragments of the TM are prepared separately and then joined at the latest-possible stage of the synthesis. Only three stages are involved in the convergent strategy, with overall yield of 51% (0.83x 100). Another important consideration in choosing a convergent protocol
SAP Convergent Charging 4.1 Upgrade Guide (v2.0) Getting Started PUBLIC 7 2 Getting Started This section of the SAP CC product document contains important information that you need to read before starting your upgrade project. This SAP product document explains how to upgrade an SAP Convergent Charging system landscape as productive
divergent tasks but that the latter lead to more output. In addition, divergent tasks produce more words and greater utterance complexity than convergent tasks. Nunan (1989) also reports the finding of his study: convergent problem-solving tasks prompted significant interactional and discourse differences with more and shorter turns than divergent
The Husband’s Secret continues to sell over 3 million copies worldwide. The book has remained on the New York Times bestseller list for over a year and is the top 10 bestseller in the UK. With the results of his work that makes Liane a writer who has three bestsellers in the world.
Convergent Evolution of Animal-Like Organelles 29 Unfortunately, it is logistically harder to study how protists achieve differentiation at finer spatial scales. Protists are capable not only of structural convergence with multicellular body plans, but also of occupying similar niches. For example, vorticellid ciliates greatly
in humans and squid function similarly, with a lens and retina, but have different origins and development. They are considered analogous traits resulting from convergent evolution (Box 1). Both deer and kangaroos successfully crop grass, sprigs, and leaves but through different means.
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