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Scaffolding, Entrenchment, and Combinatorial Modularity

Scaffolding, Entrenchment, and Combinatorial Modularity

W. C. Wimsatt
ECLT New Data - Old theories
May 2014

Insite Project

May 13, 2014

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  1. The Vienna Series in Theoretical Biology ! ! ! !

    Developing Scaffolds in Evolution, Culture, and Cognition Edited by Linnda Caporael, James R. Griesemer, and William C. Wimsatt
  2. Generative entrenchment reflects dependency relations among elements in a developing

    or operating adaptive system. Greater entrenchment yields greater conservatism in the evolution of parts or activities of the system, but generatively entrenched parts can also provide the basis for subsequent adaptive radiations of elements that depend upon it. Scaffolding is the use or generation of external parts or processes to facilitate performance of tasks by the system. Niche construction theory and Ecological Engineering are both elaborations of this idea. These two concepts, entrenchment and scaffolding, are important tools in conceptualizing the development and evolution of complex adaptive systems. I will apply them to cultural evolution, but they are equally central in evolutionary developmental biology (e.g., to pleiotropic conservation and to chaperone molecules, respectively).
  3. Simple entrenchment Here we have an evolving adaptive system with

    a recurring developmental trajectory, a life cycle, and differential entrenchment generating different degrees of evolutionary conservation. More deeply entrenched features are more likely to be preserved and thus to acquire further downstream dependent adaptations or features which presuppose their presence.
  4. Treat the life cycle as a porous spatio-temporal sausage with

    characteristic events in a developmental trajectory initiating others cycling in and out of the target system. Earlier events tend to have more downstream dependencies than later ones, increasing evolutionary conservatism. Ignoring cycles through the environment underestimates generative entrenchment inside as well as outside the system. Differential entrenchment and differential conservatism can explain and predict account of phenotypic evolution without using genes. 1 Developmental Stage Environmental Influence Causation Developmental Time Early Change Early Change Late Change J. C. Schank – ©1997/2002 b c d a
  5. von Baer’s (1828) Law: Earlier stages of diverse organisms are

    more similar than later ones. To Darwin, this suggested common origins. This earlier evolutionary conservatism is explained by the greater downstream dependencies the generative entrenchment of earlier features.
  6. This idea was significantly elaborated before big data, and particularly

    before genetic data, by Rupert Riedl (1975, English translation 1978), but since the explosion of genomic data giving comparative phylogenetic information and the possibility of detailed genomic analysis like those of Eric Davidson and Doug Erwin, analyses of genetic circuitry of increasing resolution and breadth have become possible.
  7. One result of cross phyletic comparison is the extraction of

    the kind of genomic architecture pictured here (Fig. 5.6, Davidson 2006, p. 219), indicating a kernel underlying specification in the heart progenitor field. He compares the circuitry in Drosophila and in Vertebrates, and extracts elements of the circuitry they have in common— presumably ancestral to both. Note that conserved elements are not DNA sequences, or even genes, but functional roles.
  8. For cultural evolution, developmental structure is even more crucial. Biological

    genes are acquired from a single breeding population in a single bolus at the beginning of the life cycle. But elements of culture are acquired throughout the life cycle, with earlier ones often affecting which later ones are acquired, and how they are interpreted and elaborated. They in effect confound heredity, development, and selection, making traditional age-structured models with this data forbiddingly complex. This dependency structure is crucial in skill acquisition. We pass through a series of culturally induced breeding populations as we grow older, with social structures often keyed (through schooling and curricula) to the skills we must acquire. Thus cultural evolution is structured through an articulation of internal and external structure, an “endogenetics” and “exogenetics” (Wimsatt, 2000).
  9. (Language: early onset & maturation of receptive, transmitting abilities; later

    output a function of other behaviors and timing of offspring) (Calculus: late onset of both receptive ability and transmitting ability; latter may lag behind former) (History, Philosophy, other “thick” cultural traits: cumulative knowledge accumulation and ability to transmit.) (Different reception, transmission profiles for different cultural traits) Different skills have different characteristic acquisition trajectories and modes of expression
  10. Learning of Task Complexes on Guanaro Island in the Orinoco

    Delta from S. Shennan, 2002, Genes, Memes and Human History, London, Thames and Hudson, p. 41 ! Shennan also cites (p.39) information indicating that the productivity of an 18-20 year old Ache hunter is only about 20% that of a 25-50 year-old, indicating the relevance of expertise in performance, and why some of these tasks should be taught and learned over an extended time.
  11. On the structure of genetics vs. other sciences, and generative

    entrenchment: ! “Genetics is a quantitative subject. it deals with ratios, with measurements, and with the geometrical relationships of chromosomes. ... [I]t is a mathematically formulated subject that is logically complete and self-contained.” “We have attempted to treat the subject in a way suggested by these considerations—namely as a logical development in which each step depends upon the preceding ones. This book should be read from the beginning, like a textbook of mathematics or physics, rather than in an arbitrarily chosen order, like a textbook of comparative anatomy or natural history.” “Genetics also resembles other mathematically developed subjects, in that facility in the use and understanding of its principles comes only from using them. The problems at the end of each chapter are designed to give this practice. It is important that they actually be solved.” (Preface, p. 11) ! ! --A. H. Sturtevant and G. W. Beadle, An Introduction to Genetics, New York: W. B. Saunders, 1939.
  12. Maintenance entrenchment The closed causal loop explaining the persistence of

    entrenched elements in life cycles also arises when elements help to maintain important features in a persisting adaptive system. They thus preserve the system and themselves. These “closed causal loops” maintain the entrenched elements within the life trajectory without a repeated life cycle. These “system metabolic functions” contribute to the operation of stable mature systems or the continued development of competence in a given area or set of areas through continued use or reuse of a developing capability. Thus an ontogeny can generate recurrences and entrenchments within it without passing to the next generation. This is particularly important in cultural evolution where many systems undergo extended development without obvious life-cycles.
  13. Combinatorial Entrenchments Combinatorial systems are adaptations of larger systems that

    generate many variations using elements that can be put together in multiple ways. These basic elements become modules, which can play the same or different functional roles in different systems. The combinations provide readily generated possible alternatives from which complex structures can be assembled to accomplish diverse tasks. Thus language, machine parts, amino acids and computer code are such reusable parts. These possibilities make the elements increasingly entrenched as they come to be used for diverse functions in different constructions. This allows rapid evolution—usually in an “adaptive radiation”—of the systems containing the combinatorial elements as the different possible adaptive combinations are exploited.
  14. Overlapping and Embedded Entrenchments Some writers complain that cultural change

    is ambiguous between evolution and development, and thus fits neither. This is explicable. A complex compositional structure may involve many different-sized and hierarchically composed systems reproducing on different time scales. This occurs in biological and cultural systems and in hybrids of both. Metazoans develop through multiplication and division of cells, so entrenchment in cellular processes and reproduction through mitosis is embedded in metazoan development. Entrenchments through learning and habit occur in individual ontogenies, both in biology and cognition. “Innate” factors in cognition (Wimsatt 1986, 2003) assist language acquisition (Dove 2012) or other cultural processes in the individual. New employees learn their specialized tasks in training to acquire complex sequential skills in a corporation. Cycles of repetitive learning entrench individual practices and quirks within habits, which are layered, with earlier entrenched habits modulated and entrained in later constructions employing them.
  15. Evolutionary meta-ontogeniesç Overlapping entrenchments of lineages with different life cycles

    and scopes yield hybrid lineages that fail to fit traditional categories for evolving systems. They 1. may show definite ontogenetic features, but 2. unlike organisms, may not have determinate life cycles or determinate ways of reproduction (e.g., business firms), 3. may evolve (possibly without a populational environment of exchange or competition--e.g., ecologies), and 4. may show substantial horizontal borrowing or lateral hereditary transmission compromising the individuality of the lineages, and 5. may be strongly interactive with other like entities—so strongly that (with 4) separations seem arbitrary or multiply constructable, so that it is problematic to individuate species.
  16. Units: 1. transmissible elements (TREs): artifacts, practices, ideas which are

    taught, learned, constructed, imitated (note that these include both ideational and material things) 2. individuals who develop, are socialized and trained over time (in multiple contexts) and whose earlier training affects their capabilities, exposure and receptivity Built parts of the human cognitive, normative and affective environment that scaffold acquisition and performance of knowledge and skills, and coordinates acquisition of sequential skills. Some of these can also act as reproducers on their own: ! 3. institutions – normative rules or frameworks guiding behavior [like TREs but at social/group level] e.g., social norms of behavior, legal codes, certification exams and transition rituals (confirmation, bar/bat mitzvah, graduations, marriages) 4. organizations – self-maintaining groups of individuals self-organized for a purpose [like individuals, but at a social/group level] (interest groups, firms, nations, disciplines) 5. artifact-structures – physical infrastructure maintained on trans-generational time scales providing “public goods”, or toolkits for specialist activities. Government bodies are hybrids of all three, and many/most culturally transmitted processes involve rich emic (ref Tostevin) interactions with material artifacts.
  17. We grow in a trajectory in which the environment is

    structured by these social and cultural entities and we are scaffolded in our enculturated development.
  18. Scaffolding Structure-like dynamical interactions with performing individuals that are means

    through which other structures or competencies are constructed or acquired by individuals or organizations (Thus the cell scaffolds gene replication and expression so fully that one wonders whether the relevant reproductive unit is the cell rather than the gene or genome. So also for the enculturated socialized human.) Relevant scaffolding for individuals: family structure, schools [physical], curricula, disciplines, professional societies, church, work-organization, interest-groups, governmental units, laws Scaffolding for organizations (e.g. business): articles of incorporation, corporate law, manufacturers’ organizations, chambers of commerce, distribution networks Artifacts: machine tools, clothing, housing, cars, gasoline, computers, seminar tables, software Infrastructural scaffolding: language, schools, roads, sea, rail and air networks, shopping centers, truck farming, gas, water, power, telephone, distribution warehouses and networks, public transport, ethernet
  19. Compound scaffolding: 20 story platforms + large stairs (at left)

    + ladder (middle right) + cherrypicker (bottom right) + hoists (right) + pedestrian shielding (bottom), all modular, adjustable, transportable, and easily customized (note different treatment at top) for different needs. CTS tuckpointing, Chicago, March 2007
  20. And here is some bio-cultural evolution--a parasitic vines scaffolding itself

    across a 2 lane highway (scaffolding cars which scaffold human transportation) on a wire (scaffolding telecommunications and power distribution), while animal parasites in the background (tent caterpillars) construct their reproductive niche, webbing branches together as they strips the leaves.
  21. Institutional framework (curriculum) Individuals learning specified curriculum Transmitted cultural ideas

    and practices Individuals construct institutions, their standards, and their transmitted contents. W. C. Wimsatt 11-23-01 But scaffolding in culture is much richer and more interdependent. Consider that construction and maintenance of curricula presupposes schools, classes, textbooks, textbook publishers and writers, professional societies of specialists who research, develop and report on new materials , teacher training, and certification procedures.
  22. And for a big industry, like the automotive industry, the

    yellow pages reflects the diversity of support roles and spinoff occupations
  23. Chicago 2001 Yellow Pages (consumer): Automotive Entries [spinoff scaffolding] pp

    93-184 out of 2176 at 5 columns/pg.; also ~20 more entries of form, “X”, see “Y” Entries page #’s pages Rank Air conditioning sales and service 93-95 2 Alarms and security systems 95-97 2 Appraisers 97 [.2 col] Body repair/paint 97-106 10 5 Bumpers, grilles, fenders 106 [.5 col] Buying services 106 ? Dealers: -antique/classic 107 [.3 col] -new 107-127 20 1 -used 127-131 5 Detailing 131 [1.5 col] Diagnostic 131 [.5 col] Electrical 131 [1.3 col] Floor coverings 131 [.5 col] Inspection stations 131 [.2 col] Leasing 131 [1.5 col] Locator service 132 [.2 col] Machine shop 132 [1 col] Parts/Supplies [other than dealer] -new 132 10 4 -used/rebuilt 141-144 4 -performance/race 144 [1 col] Race cars 144 [2.5 col] Rental 145-158 14 3 Repair and service 158-176 19 2 -repair and service rental 176 [.2 col] Restoration (antique/lassic) 176 [2 col] Seat covers, tops, uphostery 176 [2 col] Storage 176 [1 col] Transporters/drive-away 177-179 2 Brokers 179 [.7 col] Upholstery cleaning 179 [.3 col] Warranty processing 179 [.3 col] Wrecking 179-184 5 6 ! [“C” or manufacturing directory would have much more] ! Does not include: Manufacturing, Advertising, Distribution networks for cars, parts, fuel, Insurance. Licensing, State, federal regulation, Traffic and State police, Interstate and trucking regulation, Parking, Suburbs, and streets without sidewalks, and with cul-du-sacs. Highway, Streets and sanitation [partial], Drive ins: Motels, Fast food, Banking, Shopping malls, Suburbs, Movies, Restaurants, ...
  24. Modularity never occurs by itself. It always occurs as a

    part of some larger system that it benefits. It is easy when looking at the evolution of organisms to focus on the organism and forget its environment. So for culture. Cultural or technological evolution is always conditioned by the larger systems and structures of which they must be a part, whether in biology (the genetic code, or proteins, or vertebrae) or in technology and culture (a nut-bolt combination, computer code, or a list of words).
  25. The development of a combinatorial alphabet for the construction of

    diverse complex artifacts was crucial for the explosive growth of technology. Modularity is the key here, so I will talk about the significance and evolution of modularity, particularly in technology.
  26. Modularity is a recurrent theme in evolved objects and systems.

    ! Why? For living systems that reproduce themselves, it is unavoidable: the very act of reproduction makes modules or quasi-independent entities. Multicellularity and differentiation are modulations on this theme. For technology, it seems a natural outgrowth of the development of mass production. Why again? ! I discuss some of the features of modularity in biology and in culture. I then consider how modular parts can emerge through a feedback process between part and system level interactions using the emergence of standardized parts in the evolution of mass production as an illustrative case.
  27. Modularity is common in biology, and a topic of discussion

    for several reasons: ! 1. It is easier to make a system with lots of similar parts because there are fewer part-types to code for. ! 1a. Indeed, reproduction makes maximally identical parts to start with. ! 1b. However, any interesting machine is made of differentiated parts (1a ->? 1b = the challenge of biological metazoan development!), ! 1c. and often uses even similar parts in dissimilar roles. (differentiation; “polyfunctional parts”). !
  28. Common (especially standardized) elements can become widely used for many

    functions. [If standardized, these can generate strong constraints on structure of elements interacting with them ] Consider a nut-bolt pair, with threaded shaft and hole. ! Polyfunctional Nut-Bolt: A. Fixed connection: 1. structural rigid connector [plus lock washer] 2. shear pin 3. fixed spacer [with collars or washers] ! B. Connection fixed in 1 dimension, free in another: 4. allow free rotate (shaft) between fixed clearances ! C. Continuously adjustable connection: 5. adjust/maintain angle of radially anchored arm [low torque resistance] 6. adjust travel [screw adjusts length, to clamp as in a vise, or to raise or force apart as in a jack; high force, high mechanical advantage] 7. adjustable contact/carry current ! D. Integral part of larger mechanism: 8. measuring device [micrometer, w. calibration, ruling] 9. “rheostat” control. ! E. Complex (multiples): 10. levelers on legs of supported structure [w. “shoe”] - Adjust in 2 dimensions! 11. Bind non-steel (lightly compressible) between plates. ! Exercise: Look at a tinkertoy construction kit manual. Classify the different kinds of functions served by the basic elements of the set in the different designs. [Contrast local functions with functions in context of the whole machine.] W. C. Wimsatt 3-12-03
  29. 2. A system is easier to modify if you can

    adapt to local circumstances by changing one or a few parts without systematically changing the whole, which is both harder, and is more likely to have deleterious consequences. (“quasi-independent” parts; near-decomposability.) ! 3. If you have a small number of parts each of which can be put together in different ways, you may make a large number of different kinds of things with a small “alphabet” of parts. (“combinatorial” parts, generative “alphabets”) ! So, in summary, modular parts can be polyfunctional (as a function of their differentiated roles in a complex system), quasi-independent in their modification, and combinatorially generative.
  30. Our artifacts show massive modularity, on multiple hierarchical scales. This

    was pivotal to our technological explosion. ! It is crucial to the mass distribution, efficiency, adaptability, and complexity of our artifacts that they are modular. Modularity is also inevitable, since we engineer and assemble them out of parts. (We don’t grow them!)
  31. Entrenchment can happen rapidly and massively when a part or

    tool or property of a part becomes part of a combinatorial algebra for creating an ensemble of possible systems. These parts thus become standardized, and can serve diverse functions in different systems, which increases their standardization and fixity. Thus standards for nuts and bolts will persist indefinitely, as entrenchment compels a continued need for “metric” vs. “English” parts and tools, (e.g., for Fiats and MG’s), even though their sizes are both now expressed in the metric system. The entrenchment of a 2-digit date code in software led to the great fears of financial catastrophe in the Y2K crisis.
  32. Genesis of Modularity for Technology ! 0. non-interchangeable parts (though

    often made from the same patterns), co-tuned to work together on a system-by-system basis (e.g., parts for the “Brown Bess” musket used by Redcoats during the American revolution) ! 1. with higher accuracy, interchangeable parts (only within manufacturer*, often only at the population level--can you find a fit in that basket relatively quickly?)* Springfield Armory, 1828 ! [*also “proprietary” parts of specialty manufacturers]
  33. 2. standardized parts (across manufacturers), with coordinated setting of standards,

    which become self reinforcing in a “coordination game”. (consider S.A.E. standards for nuts and bolts) [Machine tools and measurement gauges are crucial here to generate sufficient reproducibility, while their adjustable but repeatable settings also allow the same machine tools to make diverse kinds of parts.] (comment on changes in factory organization and labor practices!) ! 3. distribution of standardized parts [e.g. hardware, electronics, plumbing, equipment] stores. This is an often ignored requirement: the right parts must be in the right place at the right time, calling for elaboration of coordinated transport mechanisms. [like metabolism]. (Comment on specialized manufacture and diffusion of machine tools, and “mechanics” using “Armory practice”.)
  34. 4. parts become more polyfunctional, and generatively entrenched. 4.1 Different

    varieties of parts arise with specialized applications, all modulations of the same basic design, as illustrated with threaded fasteners in the next slide. 4.2 Aspects that are standardized become categorical (metric and English threads are incompatible) barring use of replacement parts or tools designed for one on the other. Now generatively entrenched, they become narrowly specialized (and replaceable only wholesale) or broadly applied and virtually irreplaceable. 4.3 With innovations, where one artifact replaces another, if standard formats affect compatibility, “backwards compatibility” becomes an issue. (Can you still read old file formats with your word processor?)
  35. All of the screw threads for the screw devices represented

    in Herkimer are made according to common specifications (one of several, from different countries, and for different applications). An example of this is found under “screw thread” in Wikipedia.
  36. Form and pitch! UTS thread form and pitch technical specifications

    are currently controlled by ASME/ANSI industry standards in the United States:! ! •! ASME/ANSI B1.1 - 2003 Unified Inch Screw Threads, UN & UNR Thread Form! ! •! ASME/ANSI B1.10M - 2004 Unified Miniature Screw Threads! ! •! ASME/ANSI B1.15 - 1995 Unified Inch Screw Threads, UNJ Thread Form! ! 
 P = 1 / TeethPerInch
 H = 0.866025 * P
 H1 = 0.541266 * P
 d1 = d + 1.082532 * P
 d2 = d + 0.433013 * P
 D = d
 D1 = d1
 D2 = d2 Formulas express all dimensions as functions of P and D, generating a family of threaded connection sizes
  37. 5. chunking, and hierarchical modularity [not just screws, but coils,

    starter motors, engines, kit houses, franchises]. 5.1 leads to modular assembly stages, with sub- assemblies constructed in different places than final assembly. 5.2 leads to specialized distribution [autoparts stores, etc.], need for directories, and coordination with assembly stages (including “just in time” stocking, facilitated by computerized inventory control and containerized shipping) 5.3 subassemblies may be “black boxed” (see below)
  38. Herkimer’s remarkable text is worthy of special note: This “thesaurus”

    is organized by function and within function by kind of mechanism. It creates a “design alphabet” of alternatives. They aren’t strict functional equivalents, since each is specialized to a more particular kind of application. And they are types, not particular parts. This text also encourages engineers to break complex design problems into sub- problems (Simon’s “near-decomposability”) and to use existing solutions rather than to invent yet other variants unless absolutely necessary.
  39. So the engineer can use these to contact manufacturers for

    types of parts, either subcontracting the part, or getting further information necessary to design the specialized variant for themselves. There is often a close linkage between industry and theory, with industry influencing and scaffolding the education of engineers both in college and on the job. (The classic text on “Modern Steam Engineering” by Hiscox, was distributed (with interleaved glossy catalog pages) by the New York Belting and Packing Co.) See also Murmann 2003 on interactions between dye industry and research universities in Germany in late 19th c.
  40. 6. redesign of non-modular things for modular construction (at lower

    time, cost), often to use non-optimal but easily available components. (cf. Sears’ kit houses below). 7. competitive elimination of non-modularized and non-standardized designs that are more expensive, require more labor and knowledge to repair or support. (You can’t order a standard replacement window for a Frank Lloyd Wright house.) Standardized parts allows for pre- manufactured local availability, standardized tools, and standardized training for construction and repair.
  41. Sears Kit houses, marketed from 1908 to about 1934 in

    increasing variety and sophistication. With 30,000 parts in the average kit, coming in two or more boxcars to a railroad siding near you. Labor saving (precut and labeled), and standardized, with choices of construction quality level (a high level decision that changed hundreds to thousands of parts- specifications), mode of heating and lighting, indoor plumbing, and of course the furnishings from your Sears catalogue. Choices with generative classifications like these saved hundreds or thousands of detailed decisions.
  42. And a coordinated set of light fixtures to fit your

    trim style. (These are electric lights--you can install gas instead, and buy similar fixtures for either gas or electricity in your Sears catalogue.)
  43. Choose your door styles and then door hardware--from attic to

    basement and inside to outside. These housing designs are modular all the way through.
  44. 8. black boxing: removing ability to disassemble, 8.1 in distribution

    of parts (e.g., “accessory packages”.) 8.2 in manufacturing, generating subsystems that are designed to be replaced whole, or 8.3 in forgoing expertise for dealing with the disassembled black box. 8.4 See lost skills—e.g., blacksmithing, component repair (Can you get a radio fixed or a car generator rebuilt, as I did in Canada (not in US) on a Saturday afternoon in 1970)?
  45. 9. exploitation of combinatorial possibilities of modular design, e.g., alternatives

    in materials, selling of decorative doorframes, mantlepieces, bookcases, cabinetry complexes to be installed in Sears house. [This requires design so that the add-on accessories are consistent with each other—both stylistically and mechanically]. Or look at the number of specialized accessories for computers or cars.
  46. NOTE that modularizing something into parts can disentrench their organization

    (by making it more readily disassembled and rearranged) at the same time as they entrench the components as a common alphabet. 10. design of accessories for modularized things. [if adapted to specialized devices --> entrenchment]
  47. 11. Training for modularity: autotelic folk models: tinkertoy, lincoln log,

    erector set, lego, etc. teach engineering compositional paradigm and polyfunctionality: use same parts to make different kinds of things, using the parts in (sometimes ingeniously) different ways--and each have their own standardized parts! (Buy your kid a tinkertoy set for Christmas, and play with it!)
  48. For kids only? In his book The Box, about the

    development of containerized transport, Marc Levinson describes how Matson shipping engineer Les Harlander prototyped and tested the arrangement for a problematic lifting spreader on the shipside crane on his son’s Erector Set over Christmas, 1957.
  49. With these, we get one important concept for free: Note

    that if you are forced to return to the same or nearly the same place in successive generations, you then automatically have something that will be regarded as a “life cycle.”
  50. Here is another example, for electronic circuit components. The set

    mimics the multi- layer architecture of an IC chip. Notice how it is advertised.
  51. Bristol Pegasus Engine 1938 with accessories, which increase in number

    and complexity with performance: some scaffold engine performance (oil pump, air compressors) some others scaffold activities of pilot or operation of the airplane (tachometer, hydraulic pump)
  52. 6. redesign of non-modular things for modular construction (at lower

    time, cost), often to use non-optimal but easily available components. (cf. Sears’ kit houses below). 7. competitive elimination of non-modularized and non-standardized designs that are more expensive, require more labor and knowledge to repair or support. (You can’t order a standard replacement window for a Frank Lloyd Wright house.) Standardized parts allows for pre- manufactured local availability, standardized tools, and standardized training for construction and repair.
  53. And the same ambiguity exists for technology. After all, the

    construction and maintenance of large buildings makes a niche for workers doing the tuck- pointing, contractors specializing in assembling the scaffolding, operators and manufacturers of mechanical “cherry- pickers” and the reusable and readily adaptable scaffolding parts. CTS tuckpointing, Chicago, March 2007
  54. Darwin’s Principles Embodied— Evolution and Entrenchment of Generative Structures: Any

    evolving system must meet what Lewontin (1970) has called “Darwin’s principles”; they must: (1) have descendants which differ from one another in their properties (variation), (2) some of which are heritable (heritable variation), and (3) have varying causal tendencies to have descendants (heritable variation in fitness). These three principles are core requirements for evolution. Any population of entities meeting all three of these conditions will undergo an evolutionary process, and nothing which fail to meet all of them can do so. Think of them as logical or conceptual conditions for an evolutionary process: they key into the fundamental requirements of evolution by natural selection.
  55. Two other very general conditions reflect development’s central role in

    the evolutionary process. No interesting evolutionary process (physical or conceptual) fails to meet them. Evolving entities must also be: (4) structures generated over time so they have a developmental history (generativity), and have (5) parts which have larger or more pervasive effects than others in that production (differential entrenchment). Then different elements in the structures characteristically have downstream effects of different magnitudes. The generative entrenchment (GE) of an element is the magnitude of those effects in that generation or life cycle. Elements with larger degrees of GE are generators. This is a degree property. The GE of an element in an evolutionary unit has deep consequences for its evolutionary fate, character, rate of change, and that of systems impinging on it.