List of examples of convergent evolution

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[Note: This is the EDU Community version of the Wikipedia page, List of examples of convergent evolution].

Overview

Convergent evolution (CE) is evidence or argument for physical attractors in the phase space of dynamical possibility which guide and constrain contingently adaptive evolutionary processes into statistically predictable future-specific structure or function, in a variety of physical and informational environments. When we look at evolutionary history, the dynamics of several species morphology or function is seen to converge to particular "archetypal forms and functions" in a variety of environments.

Such attractors have been called deep structure, guiding evolutionary process in predictable ways, regardless of local environmental differences. Organismic development depends on specific initial conditions (developmental genes in the "seed"), the emergence of hierarchies of modular structure and function in the unfolding organism, and persistent constancies (physical and chemical laws, stable biomes) in the environment. Likewise, some examples of convergent evolution may be best characterized as ecological, biogeographical, stellar-planetary, or universal evolutionary development (ED) if their emergence can modeled, after adjusting for observer selection, to depend on specific universal initial conditions, emergent hierarchies, and environmental constancies.

A famous example of convergence is found in eyes, which appear to have evolved on Earth from different genetic lineages to work similarly (function) in all species, and in the case of camera eyes, to also look very similar (form) in both vertebrate and invertebrate species, like humans and octopi. One can easily advance the argument that, in universes of our type, eyes, though first created by a process of evolutionary contingency, become an archetype, a kind of general optimization for almost all eye-possessing multicelluar species in Earth-like environments, once they exist. Presumably, the previously rapidly-changing "evolutionary" gene groups that led to eye creation become part of the "developmental" genetic toolkit for eye-possessing species. Such developmental features should become increasingly strongly conserved and eventually, due to path dependency and emergent hierarchies, incapable of being changed without preventing development itself. Proving such genetic convergence arguments with evidence and theory is of course more difficult, yet it is a fertile area of investigation today.

For the best website on convergent evolution in biological systems that we know of, see Simon Conway-Morris's team's excellent Map of Life: Convergent Evolution Online.

Less-optimizing convergence (LOC) vs. optimizing convergence (OC)

GlobalvsLocalOptimum.jpg

In our mostly chaotic, contingent, and deeply nonlinear universe, we can predict that many, perhaps even the vast majority, of examples of CE will not be driven by the evolving system's discovery of some hidden general optimization function, like the discovery of the eye archetype. To understand convergence, we will need some kind of general optimization theory. Let's consider two necessary features of that theory now.

  1. We can predict that any optimization that occurs must be on a continuum, from highly-optimizing convergence, which we will refer to simply as optimizing convergence (OC), conferring advantage in all the most competitive and complex environments, to a wide variety of other cases, which we can refer to collectively as less-optimizing convergence (LOC). LOC cases would include convergence that offers only some temporary or local adaptive advantage, to just a few specific species, or in some subset of specialized or less-complex environments, convergence that offers no advantage, or convergence that is deleterious but not fatal. Names for a few general classes of LOC cases have been offered by scholars, including passive convergence, parallel evolution, etc.
  2. Optimizing convergence can occur via both physical and informational processes. Physically, we might see greater efficiency of employment of physical resources, as in Bejan's constructal law, or greater density of employment of physical resources for offense or defense, the escalation hypothesis (Vermeij 1987). Informationally, we might see efficiency or density gains via informational substitution for physical processes, what Fuller called ephemeralization, or greater general intelligence (modeling ability), greater immunity, or a more useful collective morality, offering more general and persistent adaptation to a wider range of environments than previous strategies. Intelligence also offers the ability to modify environments to suit the organism, what biologists call niche-construction, as humans extensively do today. To understand OC, we will need a theory of optimization that tells us when a physical or informational advantage is likely to be more generally adaptive, particularly in the most complex, competitive and rapidly-changing environments. We also need to know whether there are any other paths that can lead, in a competitive timeframe, toward a competitively superior new form of adaptiveness. If not, then we may have discovered a developmental portal, a global optimum that represents a bottleneck, a singular pathway toward greater adaptation at the leading edge of local complexity. Organic chemistry, RNA, photosynthesis, and oxidative phosphorylation are all potential examples of portals that all universal life must pass through first, on the way toward greater adaptive complexity. They may be the only global optima on their landscapes, at the relevant timeframes, that will allow the creation of vastly greater adaptive complexity. For more on developmental portals, see our page on evolutionary development.

Consider eyes again. For their time, eyes were "the leading edge" of general optimization, for animals, in the most morphologically complex (multicellular) environments on Earth. Andrew Parker's light switch theory (In the Blink of an Eye, 2003) proposes that the development of vision in Precambrian animals directly caused the Cambrian explosion. This is a fascinating theory, implying an intelligence-driven optimization and acceleration of morphological and functional complexity. It proposes that eyes created a vastly more competitive, discriminatory, and intelligent evolutionary environment (set of selection pressures) in multicellular evolutionary space. Once they emerged, it is easy to argue that all visible animals in that intelligence-leading environment needed eyes, or other highly effective defensive strategies, to survive. Intelligence, in this case, and perhaps generally, appears to be part of a physical and informational optimization function, in the most morphologically and functionally complex environments.

Many other examples of OC can be proposed, in the most physically and informationally complex, and rapidly changing, environments on Earth, including the necessary emergence of eukaryotes, oxidative phosphorylation, multicellularity, nervous systems, bilateral symmetry, jointed limbs, opposable thumbs, tool and language use on land (much faster-improving than aqueous environments), culture, and technology, including machine intelligence. Future science will need better theories of complexity, complexification, and optimization, to deeply understand convergence, and to distinguish the much greater variety of examples of less-optimized convergence from the most highly optimized forms.

Optimizing convergence as evolutionary development (ED)

Embryogenesis is an evo devo process.

When convergence is viewed from the perspective not of the evolving species, but from some larger systems level (the biogeography, the planet, the universe) we can view optimizing convergent evolution as a process of not simply evolution, but of evolutionary development (ED).

Evo-devo biology offers us the canonical example of evolutionary development, at the organismic system level. In organisms, most molecular and cellular processes operate chaotically, contingently, and locally adaptively, a process with many dynamical similarities to species evolution. Yet a special few of these molecular and cellular processes, driven by developmental genes and environmental constancies, are chaos-reducing, convergent, constraining, and statistically predictable, or developmental. We can generalize from organismic evo-devo to construct a general theory of ED for any replicating system.

When we claim a convergence process is an example of ED, we are not only claiming that some kind of general optimization is occurring. We are also claiming that some kind of evolutionary developmental process, with both "random" and creative evolutionary search, and predictable convergence, directionality, hierarchy, modularity, life cycle, and perhaps other features found in biological development, is being followed, at some larger systems level. We see both mostly stochastic and contingent processes, along with a few convergent and hierarchical processes, in such evolutionary and developmental phenomena as embryogenesis. Evo devo models assume such a process is going on even at the universal scale, and thus that some examples of convergence can be better understood in complex systems theory as not simply evolution, but evolutionary development.

  • Ecology offers several examples of not only evolutionary but apparent developmental change. When we look above the level of species change to ecologies, we can identify predictable patterns of ecological change, including ecological succession.
  • Biogeography offers more examples. When we look above ecologies to biogeography, we find scaling laws, like Copes rule, and biogeographic laws like Foster’s rule and Bergmann’s rule, with their predictable processes of convergent and optimizing CE, or evolutionary development. The famous convergence of form seen in placental and marsupial mammals, on separate continents, offers another example of not just evolution, but biogeographic ED. For many more examples, including convergence in intelligence traits, see Conway-Morris (2004,2015) and McGhee (2011) and our list of examples of convergent evolution in species morphology and function below.
  • Culture change offers more examples. When we look above individual cultures and do cross-cultural comparisons, we find many examples of developmental features at the leading edge of competitiveness, including inventions like fire, language, stone tools, clubs, sticks, levers, written language, hydraulic empires for our first great cities, wheels, electricity, computers. etc. In each of these cases, a high-order convergence has occurred. These and other specific examples of cultural change look not only evolutionary, but evolutionary developmental (ED). Once they exist, there's no going back, for any culture seeking to stay on the leading edge of physical and informational complexification, and general adaptiveness. We also find many examples of constraint laws that operate in social and economic systems, like physicist and EDU scholar Adrian Bejan’s constructal law, and more generally, the least action principle.
  • Stellar-Planetary change offers more examples. When we look above human culture to our planet and its star, astrophysical theory tells us that the way stars have replicated, and chemically complexified, through three different populations over billions of years, has been not only evolutionary (a variety of randomly arrived at star and planet types and distributions) but evolutionary developmental, involving a progressive drive to complexification in a predictable subset of types. Many astrobiologists and planetologists argue that a subset of chaotic and nonlinear (“evolutionary”) stellar-planetary change has reliably led, with high probability and massive parallelism, to M-class stars and Earth-like planets that are biochemically and geohomeostatically ideal for the development of archaebacterial (geothermal vent) life, and from there to prokaryotes and eukaryotes. See Nick Lane's The Vital Question (2016) for one such story.
  • Universal change offers more examples. When we look beyond stars to galaxies (which do not replicate within this universe) and to the universe as a system, several cosmologists propose that it has not only much change that is evolutionary (random, contingent, experimental), but a large subset that appears developmental. If the universe and its galaxies are a replicative system in the multiverse, as some cosmologists have proposed, such special initial conditions and constancies may have themselves self-organized in an iterative and selective process, just as biological developmental parameters have self-organized, in biological systems over multiple replications. For more on the latter idea, see our wiki page cosmological natural selection (fecund universes). The fine-tuned universe hypothesis also offers one of several examples that the initial conditions of our universe seem self-organized for the emergence of internal complexity and its persistence over billions of years. As in biological genes, only a handful of which are developmental, highly conserved, and finely-tuned, only a handful of these universal parameters seem improbably finely tuned, to a degree far beyond that we would expect through obvious observer-selection effects. See Martin Rees, Just Six Numbers, 1999 for one such account.

If universal evolutionary development is occurring, future science must show that each successive environment in the developmental hierarchy inherits certain initial conditions and physical constancies from the environment that preceded it, back to the birth of the universe, and that some of these initial conditions and constancies act to predictably constrain the future dynamics of each successive environment, to some degree. These constraints have been called developmental portals by some scholars. M-class stars and organic chemistry may be necessary portals to planets capable of generating life. Fats, proteins, and nucleic acids may be necessary portals to cells. Eyes may be necessary portals to higher nervous systems, etc. These portals must also work together to periodically produce a metasystem transition (a higher level of order or control), a new level of ED hierarchy.

Another example of predictable developmental signal, across all of these environments, may be the ever-faster complexification we see in the historical record of the most physically and informationally complex locations in our universe, since the emergence of M-class stars, Earth-like planets, and almost simultaneously, on our planet, life. This acceleration was famously summarized in Carl Sagan's metaphor of the Cosmic Calendar. Ever since August, on this calendar metaphor, leading-edge complexity environments have become exponentially faster, more complex, and more intelligent, on average, on Earth. Sagan said this phenomenon, which we can call acceleration studies, was an understudied area of science, in need of better understanding. See Sagan's The Dragons of Eden (1977) for his original account. It our hope that better models of early universe, astrophysical, chemical, biological, psychological, social, economic, technological, and other evolutionary development will help us understand our universe's emergence record of ever faster and more physically- and informationally-complex local environments.

For a deeper introduction to this topic, see our wiki page, evolutionary development.

Examples of convergent evolution (roughly scale and complexity ranked at each level of scale)

Convergent evolution—the evolutionary emergence of similar traits (forms or functions) in unrelated lineages—is rife in nature, as illustrated by the examples below. Convergence occasionally even creates cryptic species, organisms so similar in appearance that their uniqueness can only be discerned by discovering their separate breeding lineages, or analyzing their genes.

The most common cause of convergence is a similar evolutionary biome, as similar environments select for similar traits in many species occupying the same ecological niche, even when those species are only distantly related. Environmental convergence causes can be both physical and informational in nature. Species convergence on the archetypal shape of fish fins seems a primarily due to physical functional constraints (streamlining reduces drag in water). The convergence on eyes, of which there are eight major optical types in animals, apparently happened at least a dozen times in evolutionary history, presumably due to informational functional constraints (seeing allows better navigation of the environment).[1] Synapses, which emerged at least three independent times,[2] clearly offer additional informational advantages (storing memories, thinking), in adapting to complex and competitive environments. Certain forms of convergence (eyes, synapses) are particularly advantageous for surviving in informationally-complex environments, and completing against other informationally-complex species. Not simply local adaptation, but some general optimization function may exist for such environments.

Cultural convergence on particular human-technological traits (forms and functions), as seen in the use and inevitable improvement and radiation of opposable thumbs, rocks, clubs, language, levers, ropes, pulleys, wheels, math, plant and animal domestication, architecture, cities, warmaking technologies, engines, electricity, computers, etc. in cultural evolution offers clear physical and informational advantages to the humans using those technologies, in sufficiently complex environments. Again, some general optimization function, involving convergence in environments of escalating innovation and competition, seems likely to exist. Models of social development,[3] using traits like energy capture per capita, information technology, war-making capacity, and organization, offer convergence variables that are proposed to predict the competitiveness and longevity of social groups. We are early in such work, but it seems the direction we must go, to better understand cultural convergence.

Unlike Wikipedia's list of convergence examples, which are offered in no particularly useful order, as they adhere to the standard "random" and "blind" view of evolutionary process, we list our collection of convergence examples from smaller to larger in scale (molecular to ecosystem) and from less physically and informationally complex (in morphology, function, and intelligence) to more complex--a much more useful categorization scheme. While standard evolutionary theory continues to dismiss the idea that our universe appears biased to produce accelerating complexity, there is an obvious trend of accelerating complexification in the most complex of Earth's environments. In our view, this predictable complexification can be understood best by proposing that our universe appears not only to be evolving, but to be developing, a model of change we call evolutionary development.

In proteins, including enzymes and biochemical pathways

  • The existence of distinct families of carbonic anhydrase is believed to illustrate convergent evolution.
  • The use of (Z)-7-dodecen-1-yl acetate as a sex pheromone by the Asian elephant (Elephas maximus) and by more than 100 species of Lepidoptera.
  • The independent development of the catalytic triad in serine proteases independently with subtilisin in prokaryotes and the chymotrypsin clan in eukaryotes.
  • The repeated independent evolution of nylonase in two different strains of Flavobacterium and one strain of Pseudomonas.
  • The biosynthesis of plant hormones such as gibberellin and abscisic acid by different biochemical pathways in plants and fungi.[4][5]
  • ABAC is a database of convergently evolved protein interaction interfaces. Examples comprise fibronectin/long chain cytokines, NEF/SH2, cyclophilin/capsid proteins. Details are described here.
  • The independent development of three distinct hydrogenases exemplifies convergent evolution.
  • The protein prestin that drives the cochlea amplifier and confers high auditory sensitivity in mammals, shows numerous convergent amino acid replacements in bats and dolphins, both of which have independently evolved high frequency hearing for Animal echolocation|echolocation.[6][7] This same signature of convergence has also been found in other genes expressed in the mammalian cochlea.[8]

In bacteria

In functional anatomy (general)

In functional anatomy (nervous systems)

  • The notochords in chordates are like the stomochords in hemichordates.
  • Eyes, of which there are eight major optical types in animals, apparently emerged at least a dozen independent ways and times in evolutionary history, presumably due to their impressive informational functional constraints (seeing allows predictably superior navigation of the environment, in almost all environments).[9]
  • Synapses emerged at least three independent times, with three somewhat different molecular-genetic structures, in ctenophora (comb jellies), cnidaria (jellyfish) and bilateria (bilaterally symmetric animals).[10] Synapses offer constraining informational advantages (storing memories, thinking), in adapting to complex and competitive environments.
  • Bioluminescence: A symbiotic partnerships with light-emitting bacteria developed many times independently in deep-sea fish, jellyfish, and in fireflies and glow worms.

In plants

In animals

Arthropods

Pill bugs look like pill millipedes, but are actually wood lice that have converged on the same defenses, until they are difficult to tell apart
  • Assassin spiders comprise two lineages that evolved independently. They have very long necks and fangs proportionately larger than those of any other spider, and they hunt other spiders by snagging them from a distance.
  • The smelling organs of the terrestrial coconut crab are similar to those of insects.
  • Pill bugs and pill millipedes have evolved not only identical defenses, but are even difficult tell apart at a glance.
  • Silk: Spiders, silk moths, larval caddis flies, and the weaver ant all produce silken threads.
  • The praying mantis body type – raptorial forelimb, prehensile neck, and extraordinary snatching speed - has evolved not only in mantid insects but also independently in neuropteran insects Mantispidae.
  • Agriculture: Some kinds of ants, termites, and ambrosia beetles have for a long time cultivated and tend fungi for food. These insects sow, fertilize, and weed their crops. A damselfish also takes care of red algae carpets on its piece of reef; the damselfish actively weeds out invading species of algae by nipping out the newcomer.

Molluscs

  • Bivalves and the gastropods in the family Juliidae have very similar shells.
  • There are limpet-like forms in several lines of gastropods: "true" limpets, pulmonate siphonariid limpets and several lineages of pulmonate freshwater limpets.
  • Cuttlefish show similarities between cephalopod (nautili, octopods and squid) and vertebrate (Mammalia...) eyes.
  • Swim bladders – Buoyant bladders independently evolved in fishes, female octopus and siphonophores such as the Portuguese Man o' War.
  • The phylum Mollusca members such as bivalves, and phylum Brachiopoda members, the brachiopods aka lampshells, independently evolved paired hinged shells for protection. The anatomy of their soft body parts is so dissimilar, however, that they are classified in separate, independent phyla. Biologists think that clams are more closely related to earthworms than they are to brachiopods.
  • Jet propulsion in squids and in scallops: these two groups of mollusks have very different ways of squeezing water through their bodies in order to power rapid movement through a fluid. (Dragonfly larvae in the aquatic stage also use an anal jet to propel them, and Jellyfish have used jet propulsion for a very long time.)

Fish

Amphibians

Prehistoric reptiles

Extant reptiles

Avian

Mammals

The skulls of the Thylacine (left) and the Grey Wolf, Canis lupus, are almost identical, although the species are only very distantly related (different infraclasses). The skull shape of the Red Fox, Vulpes vulpes, is even closer to that of the Thylacine.[15]

In humans (biology)

  • Andeans and Tibetans living at high elevations independently developed genetic traits that let their hemoglobin bind more oxygen than sea-level humans. Ethiopians took a non-genetic route to high-altitude adaptation.[26]

In ecosystems

In biogeographies

  • Scaling laws, like Copes rule, and biogeographic laws like Foster’s rule and Bergmann’s rule offer many predictable processes of convergence.
  • The famous convergence of form seen in the species distributions and types among placental and marsupial mammals, on separate continents
  • For examples of biogeographic convergence in intelligence traits, see Conway-Morris (2004) and McGhee (2011).

In humans (culture, technology)

  • When we look above individual cultures and do cross-cultural comparisons, we find many examples of developmental features at the leading edge of competitiveness, including inventions like fire, language, stone tools, clubs, sticks, levers, written language, hydraulic empires for our first great cities, wheels, electricity, computers. etc. In each of these cases, a high-order convergence has occurred. These and other specific examples of cultural change look not only evolutionary, but evolutionary developmental (ED). Once they exist, there's no going back, for any culture seeking to stay on the leading edge of physical and informational complexification, and general adaptiveness.
  • We also find many examples of constraint laws that operate in social and economic systems, like physicist and EDU scholar Adrian Bejan’s constructal law, and the least action principle (Georgiev Georgi Y. et al. 2015).[27]

Research questions

  • How can we better develop a general theory of both optimizing convergence (OC) and less-optimizing convergence (LOC) so we can reliably differentiate between the two?
  • How much more common is LOC than OC, in various complex systems?
  • When are physical and when are informational forms of optimization more important, in various complex systems?
  • Can a general theory of optimizing convergence (OC) be created without the metaphor of evolutionary development (ED)?
  • How can we better test and develop theories of evolutionary development (ED) at all scales, from organisms to universes?
  • In the theory of evolutionary development (ED), when comparing successively emergent environments (early universe, astrophysics, chemistry, biology, psychology, and societal systems, technological systems), what are the similarities and differences between contingently adaptive ("evolutionary") processes?
  • In the theory of evolutionary development (ED), when comparing successively emergent environments , what are the similarities and differences in processes of apparent high optimization ("developmental") processes?

Books

References

  1. Fernald, Russell D (2006) Casting a Genetic Light on the Evolution of the Eye. Science 313(5795):1914-1918 DOI:10.1126/science.1127889
  2. Shen et al. (2017) Contentious relationships in phylogenomic studies can be driven by a handful of genes. Nature Ecology & Evolution. DOI:10.1038/s41559-017-0126
  3. Morris, Ian (2013) The Measure of Civilization: How Social Development Decides the Fate of Nations, Princeton U. Press.
  4. Tudzynski, B (2005) Gibberellin biosynthesis in fungi: genes, enzymes, evolution, and impact on biotechnology, Appl Microbiol Biotechnol.66(6):597–611. doi 10.1007/s00253-004-1805-1
  5. Siewers V et al. (2004) The P450 monooxygenase BcABA1 is essential for abscisic acid biosynthesis in Botrytis cinerea. Appl Environ. Microbiol. 70(7)3868–3876. doi 10.1128/AEM.70.7.3868-3876.2004
  6. Liu Y et al. (2010) Convergent sequence evolution between echolocating bats and dolphins. Current Biology 20:R53-54
  7. Liu, Y et al. (2010) Cetaceans on a molecular fast track to ultrasonic hearing. Current Biology 20:1834–1839.
  8. Davies KTJ et al. (2011) Parallel signatures of sequence evolution among hearing genes in echolocating mammals: an emerging model of genetic convergence. Heredity doi 10.1038/hdy.2011.119
  9. Fernald, Russell D (2006) Casting a Genetic Light on the Evolution of the Eye. Science 313(5795):1914-1918 DOI:10.1126/science.1127889
  10. Shen et al. (2017) Contentious relationships in phylogenomic studies can be driven by a handful of genes. Nature Ecology & Evolution. DOI:10.1038/s41559-017-0126
  11. Christidis L and Boles WE (2008). Systematics and Taxonomy of Australian Birds. CSIRO Publishing. p. 196. ISBN 978-0-643-06511-6
  12. Birn-Jeffery AV et al. (2010) Pedal claw curvature in birds, lizards and mesozoic dinosaurs--complicated categories and compensating for mass-specific and phylogenetic control. PLOS ONE 7(12):e50555. doi 10.1371/journal.pone.0050555
  13. Walter, Timothy J (2007) Sleeping With One Eye Open. Capitol Sleep Medicine Newsletter 2(6):3621–3628.
  14. Payne, RB (1997) Avian brood parasitism. In D. H. Clayton and J. Moore (eds.), Host-parasite evolution: General principles and avian models, 338–369. Oxford U. Press.
  15. Werdelin L (1986) Comparison of Skull Shape in Marsupial and Placental Carnivores, Aus. J. Zool, 34(2)109-117. doi=10.1071/ZO9860109
  16. Prothero, Donald (1988) The phylogeny of the ungulates. In: Benton, MJ (ed.) The Phylogeny and Classification of the Tetrapods, Vol. 2, Chapter 8, Clarendon Press.
  17. Gheerbrant, Emmanuel et al. (2016) Convergence of Afrotherian and Laurasiatherian Ungulate-Like Mammals: First Morphological Evidence from the Paleocene of Morocco. PLoS ONE 11(7):e0157556 doi 10.1371/journal.pone.0157556
  18. Hoffman, Lew (2004), tcnj.edu, Antelope Vs. Pronghorn, tcnj.edu. Retrieved 4/20/2017.
  19. Luo, Zhe-Xi et al. (2001) Dual origin of tribosphenic mammals. Nature 409(6816):53–57. doi 10.1038/35051023
  20. Taitt, Kyle (2013) The Curious Evolutionary History of the ‘Marsupial Wolf’, ScienceBlog.com. Retrieved 4/20/2017.
  21. Springer, J and Holley, D (2012) An Introduction to Zoology, p. 102.
  22. McGhee, George (2011) Convergent Evolution: Limited Forms Most Beautiful, MIT Press, p. 158.
  23. Liu, Y et al. (2010) Convergent sequence evolution between echolocating bats and dolphins. Current Biology 20:R53-54.
  24. Liu, Y et al. (2010) Cetaceans on a molecular fast track to ultrasonic hearing. Current Biology 20:1834–1839.
  25. Davies KTJ et al. (2011) Parallel signatures of sequence evolution among hearing genes in echolocating mammals: an emerging model of genetic convergence. Heredity doi 10.1038/hdy.2011.119
  26. Beall CM (2006) Andean, Tibetan, and Ethiopian patterns of adaptation to high-altitude hypoxia., Integr Comp Biol, 46(1):18-24. doi=10.1093/icb/icj004
  27. Georgiev, Georgi Y et al. (2015) Mechanism of organization increase in complex systems, Complexity 21(2)18-28.