17 A Constructor Theory of Adaptation: the programme
(ns meme-constructor.adaptation.post-iii0-programme
(:require [scicloj.kindly.v4.kind :as kind]
[meme-constructor.figures :as fig]))Post III.0 of Part III. Status: September 2026.
Part III asks how evolutionary biology produces design. Its answer in brief: the classic critics of adaptationism offer no rival theory of design; how far a site falls below the neutral rate measures, on real proteins, how designed it is, and the measure is graded; and in every toy the work of finding a design was done by selection, never by competition. Whether keeping a design needs competition is open.
Part I, “A Constructor Theory of Computing and Design”, owns the definitions: design, which mentions no process and no substrate, and the adaptive process. Part II, “Memes as Abstract Constructors”, reads them for ideas. Part III reads them for living things, with real data where there is any.
17.1 The question
Design is defined without a process (Definition I.5.0): a constructor is designed to the degree that most of its one-step variants perform its task much worse. An adaptive process needs variation that does not read the task and selection by the task (Definition I.5.1). The design conjecture (Conjecture I.5.12) says that adaptationism is the best theory of design. Part III asks what follows for biology: what the critics explain, how design shows up in sequence data, how coarse the selecting environment may be, which programs can carry design, what sex and symbiogenesis change, and what a brain needs to make good ideas.
17.2 The answer
- The critics explain non-designs. Spandrels, developmental constraint and self-organisation explain traits that fail the alternatives condition (D2). Exaptation explains no fine-tuning for the new task. Drift and hitchhiking fail the selection condition (A3). None says how fine-tuning arises, so none is a rival (post III.1). Rates of change tell a design from a non-design for traits that vary on their own; for traits that always vary together only an intervention can.
- Design is graded, and the constraint measures it. Kimura’s constraint \(1 - k/\mu\) is the degree of fine-tuning of a site. On real proteins it separates the insulin chains from the C-peptide and the haem pocket from the surface. The C-peptide, at 0.56, is weakly designed. Design being made shows as a constraint that switches on at sites that gain a task and off at sites that lose one (post III.2). A lasting excess \(k > \mu\) appears only when the task keeps moving faster than a neutral site mutates (post III.3, Proposition III.3.12).
- The environment is a coarse constructor. \(S = 4N_e s\) measures selection against drift. The constraint rises smoothly with \(S\), centred near 2, and small populations lose weakly selected sites first. This belongs to the process, not to the definition of design (post III.3).
- A design is found along a ridge. What a process needs is a ridge of partly working variants leading up to the design, not a large neutral network around it (post III.4).
- Sex and merging. Sex speeds up design only when new small points arise while others still sweep. A merge of two lineages is a crossover across lineages and wins only by importing selection done elsewhere (post III.5).
- The brain. Ideas that nothing removes still accumulate design, as long as selection reads the task somewhere: in what attention picks, or in the rule that decides which idea stays. A budget of variation does no work of its own, and ideas that persist and vary in place search cumulatively without being copied (post III.6).
Competition. No toy in the book showed that competition helps to find a design; each showed that selection is needed. Where Part III measures competition, it measures a property of a mechanism that implements selection: its strength against drift through \(N_e\) (post III.3) and its unit, the genome without sex and the allele with it (post III.5). What is open is keeping. The first evidence is from Part II: receivers that check their copies against the world kept most of a tradition’s content with no selection among hosts (post 5, Observation 5.10).
- every toy needed selection
- no toy showed that competition helps
- as a property of a mechanism that implements selection
- its strength against drift, through N_e (III.3)
- its unit: genome without sex, allele with it (III.5)
- first evidence from Part II: receivers that check copies against the world kept most content
- with no selection among hosts (post 5)
17.3 Where the definitions live
Design, with the knowledge, alternatives and fine-tuning conditions (D1–D3), is Definition I.5.0 of post I.5; post III.1 cites it as Definition III.1.1. The adaptive synthesis task (C5), with unspecific variation (A1′), selection (A3) and the property competition (A2), is Definition I.5.1 of the same post. Part III owns the biology: design and the adaptive process in biology (AD1) to symbiogenesis as merging constructors (AD10), and the experiments on real proteins and in toys (Y1–Y9).
17.4 Where Part III sits
| Who | What they provide | What Part III did with it |
|---|---|---|
| Marletto (2015) | the appearance of design as fine-tuning; the environment as a crude constructor | fine-tuning read as a degree over one step; non-containment split into a relative and a strong version |
| Williams (1966), Dawkins (1986), Dennett (1995) | explanatory adaptationism | stated as the design conjecture for biology |
| Gould & Lewontin (1979), Gould & Vrba (1982), Kauffman (1993) | spandrels, constraints, exaptation, self-organisation | each read as explaining a non-design |
| Godfrey-Smith (2001) | three adaptationisms | the explanatory one defended |
| Kimura (1962, 1968, 1983), Ohta (1973, 1992) | the neutral rate, functional constraint, fixation probability | the constraint read as the degree of fine-tuning |
| Maynard Smith (1970), Schuster et al. (1994), Wagner (2005) | protein space, neutral networks | tested against a definition of design: the ridge mattered, the target’s network did not |
| Fisher (1930), Muller (1932, 1964), Felsenstein (1974), Watson (2006), Sagan (1967) | the advantage of sex, the ratchet, compositional evolution, endosymbiosis | read as variation constructors |
| Campbell (1960), Edelman (1987), Calvin (1987), Fernando et al. (2010) | the Darwinian brain | replication not needed to find the toy’s points |
Explanatory adaptationism is not new, and neither is functional constraint as a measure. What Part III adds is one definition from which it follows why the rate measures design and why the critiques explain non-designs, tested on real proteins and in toys where the truth is known. The single-site balance of Proposition III.3.3 is a known result (Bulmer 1991), and so is the sweep argument of Proposition III.5.2 (Crow & Kimura 1965; Maynard Smith 1971).
17.5 The posts
The map of Part III: each post, its question and its answer.
An optional post III.7 would test the conservation pattern in culture (AD8) of post 7 on manuscript traditions, if a suitable collated data set exists. It is planned, not written.
Reading order. The order of dependence is Part I, then Part II, then Part III. Read post I.5 and post 7 before post III.1. Post III.2 can be read on its own.
17.6 Open problems
- under ongoing mutation, with and without competition
- the central open question of the book (post I.5)
- Conjecture III.4.10, stated after the result, untested
- keep the target's network, cut the ridge below it
- D2 is stated for single constructors
- the reach of recombination and of a merge depends on the rest of the population
17.7 References
Only works cited in this post. Entries marked “verified in post x” were checked online when that post was written. The exact passages are given there.
- Bulmer, M. (1991). The selection-mutation-drift theory of synonymous codon usage. Genetics 129, 897–907. (verified in post III.3)
- Calvin, W. H. (1987). The brain as a Darwin machine. Nature 330, 33–34. (verified in post 7)
- Campbell, D. T. (1960). Blind variation and selective retention in creative thought as in other knowledge processes. Psychological Review 67, 380–400. (verified in post 7)
- Crow, J. F. & Kimura, M. (1965). Evolution in sexual and asexual populations. American Naturalist 99, 439–450. (verified in post III.5)
- Dawkins, R. (1986). The Blind Watchmaker. Longman. (verified in post III.1: publisher and year)
- Dennett, D. C. (1995). Darwin’s Dangerous Idea. Simon & Schuster. (verified in post III.1)
- Edelman, G. M. (1987). Neural Darwinism: The Theory of Neuronal Group Selection. Basic Books. (verified in post 7)
- Felsenstein, J. (1974). The evolutionary advantage of recombination. Genetics 78, 737–756. (verified in post III.5)
- Fernando, C., Goldstein, R. & Szathmáry, E. (2010). The neuronal replicator hypothesis. Neural Computation 22(11), 2809–2857. (verified in post 7)
- Fisher, R. A. (1930). The Genetical Theory of Natural Selection. Clarendon Press. (verified in post III.5)
- Godfrey-Smith, P. (2001). Three kinds of adaptationism. In S. H. Orzack & E. Sober (eds.), Adaptationism and Optimality, 335–357. Cambridge University Press. (verified in post III.1)
- Gould, S. J. & Lewontin, R. C. (1979). The spandrels of San Marco and the Panglossian paradigm. Proc. R. Soc. B 205, 581–598. (verified in post 7)
- Gould, S. J. & Vrba, E. S. (1982). Exaptation—a missing term in the science of form. Paleobiology 8, 4–15. (verified in post III.1)
- Kauffman, S. A. (1993). The Origins of Order. Oxford University Press. (verified in post III.1)
- Kimura, M. (1962). On the probability of fixation of mutant genes in a population. Genetics 47, 713–719. (verified in post III.3)
- Kimura, M. (1968). Evolutionary rate at the molecular level. Nature 217, 624–626. (verified in post 7)
- Kimura, M. (1983). The Neutral Theory of Molecular Evolution. Cambridge University Press. (verified in post 7)
- Marletto, C. (2015). Constructor theory of life. J. R. Soc. Interface 12: 20141226. arXiv:1407.0681. (verified in post III.3)
- Maynard Smith, J. (1970). Natural selection and the concept of a protein space. Nature 225, 563–564. (verified in post 7)
- Maynard Smith, J. (1971). What use is sex? Journal of Theoretical Biology 30, 319–335. (verified in post III.5: bibliographic data)
- Muller, H. J. (1932). Some genetic aspects of sex. American Naturalist 66, 118–138. (verified in post III.5)
- Muller, H. J. (1964). The relation of recombination to mutational advance. Mutation Research 1, 2–9. (verified in post III.5)
- Ohta, T. (1973). Slightly deleterious mutant substitutions in evolution. Nature 246, 96–98. (verified in post III.3)
- Ohta, T. (1992). The nearly neutral theory of molecular evolution. Annual Review of Ecology and Systematics 23, 263–286. (verified in post 7)
- Sagan, L. [Margulis, L.] (1967). On the origin of mitosing cells. Journal of Theoretical Biology 14, 225–274. (verified in post III.5)
- Schuster, P., Fontana, W., Stadler, P. F. & Hofacker, I. L. (1994). From sequences to shapes and back: a case study in RNA secondary structures. Proc. R. Soc. Lond. B 255, 279–284. (verified in post III.4)
- Wagner, A. (2005). Robustness and Evolvability in Living Systems. Princeton University Press. (verified in post III.4)
- Watson, R. A. (2006). Compositional Evolution. MIT Press. (verified in post III.5)
- Williams, G. C. (1966). Adaptation and Natural Selection. Princeton University Press. (verified in post III.1)
source: book2/notebooks/meme_constructor/adaptation/post_iii0_programme.clj