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Evidence record

How does a cell know what to become?

Every sentence on the exploration belongs to at least one claim below. Each says what kind of statement it is, what it rests on, what the evidence does not establish, and how far it was checked. Nothing here is a score, and none of it is a verdict on a belief or a theory.

Last checked 24 September 2026.

  • Source checked: 40
  • A judgement, not a fact: 6
  • Partly checked: 3
  • Presented as open: 1

If something here is wrong, misquoted, out of date or unfair, write to support@unknownoceans.com and give the claim number, which does not change.

What the question takes for granted

A scientific question in developmental biology, put in a figure of speech: cells do not know anything, they respond to signals. What is open is which mechanisms turn those responses into anatomy, which molecules carry them, and how the result is so reliable.

  • A cell’s fate depends on signals from the cells around it

    Established

    Established for positional information by molecular examples: a gradient in the fly embryo and a growth factor in the frog that triggers different fates at different concentrations.

  • One mechanism does the patterning

    Contested

    The page reports two, self-organisation and positional information, and Green and Sharpe argue they combine; the three ways they propose are presented by them as a hypothesis.

  • Digits are laid down as a Turing pattern

    Contested

    Green and Sharpe, co-authors of the two digit papers, say the evidence points overwhelmingly to it. A later review warns that a simulated pattern resembling a real one is not enough to conclude the mechanism.

How the question is labelled

Claim: From one cell, a hand

Kind
Framing. Signposting. It asserts nothing a source could check.

Claim: Development

Kind
Framing. Signposting. It asserts nothing a source could check.

The question

Claim: A single fertilised cell divides into a body with fingers in the right places

Kind
What the field holds. The settled view of a field, as a review, a consensus statement or a reference work gives it. Not one study.
Review
Source checked. The cited passage was read, and it says this.

  • Supports

    Pattern formation mechanisms of self-organizing reaction-diffusion systemsabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Research in animals · Review of the field

    The source reads: Embryonic development is a largely self-organizing process, in which the adult body plan arises from a ball of cells with initially nearly equal potency.

  • Context

    The chemical basis of morphogenesisp. 37, introduction

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Model

    The source reads: The purpose of this paper is to discuss a possible mechanism by which the genes of a zygote may determine the anatomical structure of the resulting organism.

Later work looked for

Textbook embryology; not a finding later work revises.

Claim 3 · checked 24 September 2026 · AI-assisted audit

Claim: and the instructions are not a blueprint.

Kind
This page’s reading. A judgement the page makes from the evidence. Others read it differently.
Review
A judgement, not a fact. Reviewed for whether it is fairly put and follows from the checked claims. No source can confirm it.

The page’s own framing. It follows from claims 15 and 22: in the Turing account the spacing comes from the chemistry and the genes tune it rather than drawing each element.

Claim 4 · checked 24 September 2026 · AI-assisted audit

Claim: The genome does not contain a plan of the body.

Kind
This page’s reading. A judgement the page makes from the evidence. Others read it differently.
Review
A judgement, not a fact. Reviewed for whether it is fairly put and follows from the checked claims. No source can confirm it.

The page’s reading of the two mechanisms it describes. "Plan" means a stored picture of the anatomy; the genome does carry the genes whose products produce and read the signals.

What this does not establish

A figure of speech rather than a finding. No source tests the proposition that a genome contains no plan; the sources describe mechanisms that do not need one.

Claim 5 · checked 24 September 2026 · AI-assisted audit

Claim: Pattern arises from cells reacting to each other and to chemical gradients

Kind
What the field holds. The settled view of a field, as a review, a consensus statement or a reference work gives it. Not one study.
Review
Source checked. The cited passage was read, and it says this.

The two ideas are self-organisation (reaction-diffusion) and positional information from gradients, the subject of the whole of Green and Sharpe 2015.

What this does not establish

Other patterning mechanisms exist; Green and Sharpe name the clock-and-wave mechanism for somites.

Later work looked for

Europe PMC, 2019 on, reviews on Turing and reaction-diffusion systems in development: Landge 2020 says how common the mechanism is remains unclear, Vittadello 2021 calls its developmental role firmly established; both added to the page.

Claim 6 · checked 24 September 2026 · AI-assisted audit

Claim: and a mathematical account of how uniform tissue produces regular structures was published in 1952

Kind
Historical claim. A statement about the past that historical evidence can test.
Review
Source checked. The cited passage was read, and it says this.

  • Supports

    The chemical basis of morphogenesistitle page and abstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Model

    The source reads: a system of chemical substances, called morphogens, reacting together and diffusing through a tissue ... although it may originally be quite homogeneous, may later develop a pattern or structure due to an instability of the homogeneous equilibrium, which is triggered off by random disturbances

Claim 7 · checked 24 September 2026 · AI-assisted audit

Claim: and matched to mouse limbs sixty years later.

Kind
What scholars argue. A report of what specialists argue, or where they disagree.
Review
Source checked. The cited passage was read, and it says this.

What this does not establish

Matched means the mouse results fit a Turing model: the 2012 authors reproduced the mutant series in a computer model, while the core molecules of the mechanism were still unknown to them.

Later work looked for

Europe PMC, 2013 on, "Hox digit Turing wavelength" and "Sox9 Turing digit": later work extends the account (Marcon 2016 five-node network, Onimaru 2016 in catshark fins) and a 2015 review of distinguishing periodic-patterning models; nothing found that overturns the result.

Claim 8 · checked 24 September 2026 · AI-assisted audit

Claim: There is no picture of a hand in the genome. There is no list of where to put the fingers.

Kind
This page’s reading. A judgement the page makes from the evidence. Others read it differently.
Review
A judgement, not a fact. Reviewed for whether it is fairly put and follows from the checked claims. No source can confirm it.

The page’s framing, restating claim 5. It follows from claims 22 and 37: digit spacing comes out of a self-organising process and digit identity from a gradient, neither stored as a layout.

Claim 9 · checked 24 September 2026 · AI-assisted audit

Claim: What there is, is a set of rules about how cells respond to their neighbours, and the pattern is an outcome of running those rules rather than a thing that was stored.

Kind
This page’s reading. A judgement the page makes from the evidence. Others read it differently.
Review
A judgement, not a fact. Reviewed for whether it is fairly put and follows from the checked claims. No source can confirm it.

The page’s summary of the self-organising account in claims 12 to 15, stated as a reading rather than a finding.

What this does not establish

Positional information, claim 37, is also part of the story, and there the cells read a gradient set up from elsewhere rather than only from their neighbours.

Claim 10 · checked 24 September 2026 · AI-assisted audit

How pattern arises

Claim: How pattern arises

Kind
Framing. Signposting. It asserts nothing a source could check.

Pattern can make itself

Claim: Pattern can make itself

Kind
What a model says. What a theory or model predicts or describes, which is not the same as what has been observed.
Review
Source checked. The cited passage was read, and it says this.

  • Supports

    The chemical basis of morphogenesisabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Model

    The source reads: a system of chemical substances, called morphogens, reacting together and diffusing through a tissue ... although it may originally be quite homogeneous, may later develop a pattern or structure due to an instability of the homogeneous equilibrium, which is triggered off by random disturbances

What this does not establish

A mathematical result about a model system. That real tissues pattern this way is a separate, empirical question, taken up in claims 18 to 25 and 46 to 52.

Claim 12 · checked 24 September 2026 · AI-assisted audit

Claim: In 1952 Alan Turing showed mathematically that two substances reacting together and diffusing through a tissue can turn a uniform field into a regular pattern.

Kind
What a model says. What a theory or model predicts or describes, which is not the same as what has been observed.
Review
Source checked. The cited passage was read, and it says this.

  • Supports

    The chemical basis of morphogenesisabstract; section 6

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Model

    The source reads: a system of chemical substances, called morphogens, reacting together and diffusing through a tissue ... may later develop a pattern or structure due to an instability of the homogeneous equilibrium ... It will be assumed at first that there are only two morphogens

What this does not establish

Turing analysed idealised systems, chiefly a ring of cells, and presented the theory as suggesting that well-known physical laws may be sufficient, not as identifying any real substance.

Claim 13 · checked 24 September 2026 · AI-assisted audit

Claim: A homogeneous equilibrium goes unstable under random disturbance, and in the case he found most interesting what appears is a set of stationary waves.

Kind
What a model says. What a theory or model predicts or describes, which is not the same as what has been observed.
Review
Source checked. The cited passage was read, and it says this.

  • Supports

    The chemical basis of morphogenesisabstract; section 8, case (d)

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Model

    The source reads: may later develop a pattern or structure due to an instability of the homogeneous equilibrium, which is triggered off by random disturbances. ... It is faund that there are six essentially different forms which this may take. In the most interesting form stationary waves appear on the ring.

    "faund" is the scan’s OCR for "found".

What this does not establish

Stationary waves are one of six forms of instability Turing found; others give synchronised or travelling oscillations.

Corrected

24 September 2026. Previously: “A homogeneous equilibrium goes unstable under random disturbance, and what appears is a set of stationary waves whose spacing, what he called the chemical wavelength, is set by the reaction and diffusion rates rather than by the size of the tissue.” Turing finds six forms the instability can take, of which stationary waves are the most interesting, and says the wavelengths on a finite ring do depend on its size; the chemical wavelength is the one the chemistry would choose, approximated by what fits. The page had made stationary waves the only outcome and the tissue size irrelevant.

Claim 14 · checked 24 September 2026 · AI-assisted audit

Claim: Their natural spacing, what he called the chemical wavelength, is set by the reaction and diffusion rates rather than by the size of the tissue; a finite tissue makes do with the nearest spacing that fits.

Kind
What a model says. What a theory or model predicts or describes, which is not the same as what has been observed.
Review
Source checked. The cited passage was read, and it says this.

  • Supports

    The chemical basis of morphogenesissection 8, p. 51

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Model

    The source reads: a ‘chemical wave-length’ which does not depend on the dimensions of the ring. ... the chemical wave-length is true wave-length which is achieved whenever possible, but that on a ring it is necessary to ‘make do’ with an approximation which divides exactly into the circumference.

  • Qualifies

    Pattern formation mechanisms of self-organizing reaction-diffusion systemsabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Review of the field

    The source reads: Recent studies have addressed this shortcoming and extended the reaction-diffusion theory to realistic multi-component networks. These efforts have challenged the generality of previous central tenets derived from the analysis of simplified systems

What this does not establish

Derived for an idealised ring of cells and continuous tissue. Later analyses of networks with three or more components find patterning conditions that differ from the two-substance case.

Corrected

24 September 2026. Previously: “whose spacing, what he called the chemical wavelength, is set by the reaction and diffusion rates rather than by the size of the tissue.” See claim 14: the finite tissue approximates the chemical wavelength.

Claim 15 · checked 24 September 2026 · AI-assisted audit

Claim: It was a purely theoretical result, published in a paper about morphogenesis,

Kind
Historical claim. A statement about the past that historical evidence can test.
Review
Source checked. The cited passage was read, and it says this.

  • Supports

    The chemical basis of morphogenesisabstract and section 2

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Model

    The source reads: The investigation is chiefly concerned with the onset of instability. ... In this section a mathematical model of the growing embryo will be described.

Claim 16 · checked 24 September 2026 · AI-assisted audit

Claim: and it stayed theoretical for a long time because nobody could point to the substances.

Kind
What scholars argue. A report of what specialists argue, or where they disagree.
Review
Source checked. The cited passage was read, and it says this.

What this does not establish

Green and Sharpe give other reasons for the neglect as well: the fixed wavelength, early findings that the patterns were sensitive to noise, and the rise of positional information.

Claim 17 · checked 24 September 2026 · AI-assisted audit

Digits behave the way the mathematics says

Claim: Digits behave the way the mathematics says

Kind
What scholars argue. A report of what specialists argue, or where they disagree.
Review
Source checked. The cited passage was read, and it says this.

What this does not establish

The authors’ reading of mouse mutants with computer modelling, in mice. The review that endorses it shares an author with the paper.

Claim 18 · checked 24 September 2026 · AI-assisted audit

Claim: A 2012 study started from mice lacking Gli3, which already grow extra digits, and removed distal Hox genes in stages on top of that.

Kind
Experimental result. What an experiment or trial found, under its own conditions. A result in animals, cells or a simulation is not a result in people.
Review
Source checked. The cited passage was read, and it says this.

  • Supports

    Hox Genes Regulate Digit Patterning by Controlling the Wavelength of a Turing-Type Mechanismabstract (author manuscript)

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Research in animals · Experiment

    The source reads: the progressive reduction in Hoxa13 and Hoxd11-Hoxd13 genes (hereafter referred to as distal Hox genes) from the Gli3-null background results in progressively more severe polydactyly, displaying thinner and densely packed digits

  • Supports

    Hox Genes Regulate Digit Patterning by Controlling the Wavelength of a Turing-Type Mechanismmain text, triple-mutant allelic series; Fig. 2

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Research in animals · Experiment

    The source reads: The number of digits increased from 7 to 9 (typical of Gli3XtJ/XtJ) to 8 to 9 when one functional allele of both Hoxa13 and Hoxd11-13 was removed; further, to 9 to 11 when both Hoxd11-13 alleles were removed

What this does not establish

In mice. The Gli3-null limbs had 7 to 9 digits before any Hox gene was removed; the series used Hoxa13, Hoxd11-13 and Gli3 alleles.

Later work looked for

Europe PMC, 2013 on, "Hox digit Turing wavelength" and "Sox9 Turing digit": later work extends the account (Marcon 2016 five-node network, Onimaru 2016 in catshark fins) and a 2015 review of distinguishing periodic-patterning models; nothing found that overturns the result.

Claim 19 · checked 24 September 2026 · AI-assisted audit

Claim: Each step made the polydactyly worse: more digits, thinner and more densely packed.

Kind
Experimental result. What an experiment or trial found, under its own conditions. A result in animals, cells or a simulation is not a result in people.
Review
Source checked. The cited passage was read, and it says this.

  • Supports

    Hox Genes Regulate Digit Patterning by Controlling the Wavelength of a Turing-Type Mechanismabstract (author manuscript)

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Research in animals · Experiment

    The source reads: the progressive reduction in Hoxa13 and Hoxd11-Hoxd13 genes (hereafter referred to as distal Hox genes) from the Gli3-null background results in progressively more severe polydactyly, displaying thinner and densely packed digits

  • Supports

    Hox Genes Regulate Digit Patterning by Controlling the Wavelength of a Turing-Type Mechanismmain text, triple-mutant allelic series; Fig. 2

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Research in animals · Experiment

    The source reads: The number of digits increased from 7 to 9 (typical of Gli3XtJ/XtJ) to 8 to 9 when one functional allele of both Hoxa13 and Hoxd11-13 was removed; further, to 9 to 11 when both Hoxd11-13 alleles were removed

  • Supports

    Hox Genes Regulate Digit Patterning by Controlling the Wavelength of a Turing-Type Mechanismmain text, triple-mutant allelic series

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Research in animals · Experiment

    The source reads: The increase in digit number as distal Hox genes were removed did not rely on increased AP handplate size ... but rather on a reduced wavelength as digits were thinner and had narrower gaps between them, while remaining regularly spaced

What this does not establish

In mice, on a Gli3-null background: digit number rose from 7 to 9 to at least 12 to 14 as Hox alleles were removed, and the extra digits came from a shorter wavelength rather than a wider hand plate.

Later work looked for

Europe PMC, 2013 on, "Hox digit Turing wavelength" and "Sox9 Turing digit": later work extends the account (Marcon 2016 five-node network, Onimaru 2016 in catshark fins) and a 2015 review of distinguishing periodic-patterning models; nothing found that overturns the result.

Claim 20 · checked 24 September 2026 · AI-assisted audit

Claim: With computer modelling, the authors read that as a Turing-type mechanism whose wavelength the dose of those genes modulates.

Kind
What scholars argue. A report of what specialists argue, or where they disagree.
Review
Source checked. The cited passage was read, and it says this.

What this does not establish

A modelling interpretation: in the authors’ model both Hox levels and Fgf signalling modulate the wavelength.

Corrected

24 September 2026. Previously: “With computer modelling, the authors read that as a Turing-type mechanism whose wavelength the dose of those genes is setting.” The abstract says the Hox dose "modulates" the wavelength, not that it sets it.

Claim 21 · checked 24 September 2026 · AI-assisted audit

Claim: On that account the digits are stripes, their spacing is a wavelength, and the genes tune it rather than specifying each one.

Kind
What a model says. What a theory or model predicts or describes, which is not the same as what has been observed.
Review
Source checked. The cited passage was read, and it says this.

What this does not establish

The account is of where digits form, not of which digit is which: Green and Sharpe attribute digit identity to a separate gradient.

Claim 22 · checked 24 September 2026 · AI-assisted audit

Claim: The paper argues for it rather than demonstrating it,

Kind
What scholars argue. A report of what specialists argue, or where they disagree.
Review
Source checked. The cited passage was read, and it says this.

The authors’ own verb is "argue for".

What this does not establish

The authors say the core molecules of the mechanism were unknown, and that the phenotypes cannot be explained by a positional-information gradient; the Turing reading rests on the fit of their model.

Claim 23 · checked 24 September 2026 · AI-assisted audit

Claim: and notes that the mutant digits resemble the endoskeleton of a fish fin,

Kind
Observation. Something measured or seen, as the named source reports it.
Review
Source checked. The cited passage was read, and it says this.

What this does not establish

A resemblance of form, which the authors describe in the discussion; no fins were examined in the paper.

Later work looked for

Europe PMC, 2013 on, "fin-to-limb Turing": Onimaru and others 2016 report the Bmp-Sox9-Wnt network patterning catshark fin elements, which is consistent with the resemblance; nothing that changes it.

Claim 24 · checked 24 September 2026 · AI-assisted audit

Claim: which would make five fingers a modification of an older mechanism.

Kind
Hypothesis. A proposed explanation, not an established one.
Review
Source checked. The cited passage was read, and it says this.

What this does not establish

An evolutionary inference from a resemblance in mouse mutants. The authors call it evidence of a conserved mechanism; no fish were studied in the 2012 paper.

Later work looked for

Europe PMC, 2013 on, "fin-to-limb Turing": Onimaru and others 2016 find the same network in catshark fins and propose fin and limb diversity came from re-organising it; supportive, not decisive.

Claim 25 · checked 24 September 2026 · AI-assisted audit

Claim: How a pattern appears without a plan

Kind
Framing. Signposting. It asserts nothing a source could check.

Claim: Start uniform

Kind
Framing. Signposting. It asserts nothing a source could check.

Claim: A field of cells with no differences worth speaking of, and two signals that spread at different rates.

Kind
What a model says. What a theory or model predicts or describes, which is not the same as what has been observed.
Review
Source checked. The cited passage was read, and it says this.

  • Supports

    Positional information and reaction-diffusion: two big ideas in developmental biology combinesection on the principles of RD

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Review of the field

    The source reads: Starting from a homogeneous spatial pattern, even small random molecular fluctuations can cause the activator to have slightly higher concentrations at certain positions ... the inhibitor is allowed to diffuse faster than the activator

  • Qualifies

    Pattern formation mechanisms of self-organizing reaction-diffusion systemssection on robust Turing networks

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Review of the field

    The source reads: enable the design and discovery of robust Turing networks with smaller differences or even equal diffusivities of the involved signaling molecules

What this does not establish

The textbook two-signal case. Later analyses find networks of three or more components that pattern with little or no difference in diffusion rates.

Claim 28 · checked 24 September 2026 · AI-assisted audit

Claim: Amplify a difference

Kind
Framing. Signposting. It asserts nothing a source could check.

Claim: In the best-known version, a short-range signal activates its own production and a long-range one suppresses it.

Kind
What a model says. What a theory or model predicts or describes, which is not the same as what has been observed.
Review
Source checked. The cited passage was read, and it says this.

  • Supports

    Positional information and reaction-diffusion: two big ideas in developmental biology combinesection on the principles of RD; Mode 2, on the digits

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Review of the field

    The source reads: we can consider Turing’s original morphogens as short-range activators coupled with long-range inhibitors (Gierer and Meinhardt, 1972) ... more complex than the popular activator-inhibitor mechanism

  • Qualifies

    Positional information and reaction-diffusion: two big ideas in developmental biology combineFig. 2 legend

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Research in animals · Review of the field

    The source reads: In the limb buds (ii), the positions of future digits are created as a Turing pattern driven by a feedback loop between Wnt and Bmp signalling and the transcription factor Sox9. This is equivalent to a substrate-depletion Turing model, rather than an activator-inhibitor model.

What this does not establish

The activator-inhibitor picture is Gierer and Meinhardt’s 1972 reading, not Turing’s wording, and it is one of two broad kinds. The digit network is the other kind, substrate depletion, with three molecules.

Corrected

24 September 2026. Previously: “The short-range signal activates its own production; the long-range one suppresses it.” Green and Sharpe describe two broad categories of Turing system, activator-inhibitor and substrate-depletion, and place the digit network in the second. The step described the first as if it were the mechanism, beside a step about digits.

Claim 30 · checked 24 September 2026 · AI-assisted audit

Claim: Any tiny fluctuation is amplified locally and suppressed at a distance.

Kind
What a model says. What a theory or model predicts or describes, which is not the same as what has been observed.
Review
Source checked. The cited passage was read, and it says this.

What this does not establish

Describes the activator-inhibitor model; in the substrate-depletion kind the two patterns are out of phase rather than peaking together.

Claim 31 · checked 24 September 2026 · AI-assisted audit

Claim: Settle into a spacing

Kind
Framing. Signposting. It asserts nothing a source could check.

Claim: The result is regular stripes or spots whose wavelength depends on the rates.

Kind
What a model says. What a theory or model predicts or describes, which is not the same as what has been observed.
Review
Source checked. The cited passage was read, and it says this.

What this does not establish

What the model does. In a real limb the spacing also varies with position, which Green and Sharpe attribute to a gradient modulating the wavelength.

Claim 33 · checked 24 September 2026 · AI-assisted audit

Claim: Change the rates and the spacing changes.

Kind
What a model says. What a theory or model predicts or describes, which is not the same as what has been observed.
Review
Source checked. The cited passage was read, and it says this.

What this does not establish

A property of the model. Which rates a real tissue changes, and how, is what claims 35 and 42 are about.

Claim 34 · checked 24 September 2026 · AI-assisted audit

Claim: In the mouse experiment what changed was the dose of Hox genes, and the digits grew thinner and closer together.

Kind
Experimental result. What an experiment or trial found, under its own conditions. A result in animals, cells or a simulation is not a result in people.
Review
Source checked. The cited passage was read, and it says this.

  • Supports

    Hox Genes Regulate Digit Patterning by Controlling the Wavelength of a Turing-Type Mechanismabstract (author manuscript)

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Research in animals · Experiment

    The source reads: the progressive reduction in Hoxa13 and Hoxd11-Hoxd13 genes (hereafter referred to as distal Hox genes) from the Gli3-null background results in progressively more severe polydactyly, displaying thinner and densely packed digits

  • Supports

    Hox Genes Regulate Digit Patterning by Controlling the Wavelength of a Turing-Type Mechanismmain text, triple-mutant allelic series

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Research in animals · Experiment

    The source reads: The increase in digit number as distal Hox genes were removed did not rely on increased AP handplate size ... but rather on a reduced wavelength as digits were thinner and had narrower gaps between them, while remaining regularly spaced

What this does not establish

That the Hox dose acts on the model’s rates is the authors’ modelling interpretation, not something the experiment measured.

Later work looked for

Europe PMC, 2013 on, "Hox digit Turing wavelength" and "Sox9 Turing digit": later work extends the account (Marcon 2016 five-node network, Onimaru 2016 in catshark fins) and a 2015 review of distinguishing periodic-patterning models; nothing found that overturns the result.

Corrected

24 September 2026. Previously: “Change the rates and you change the number of digits, which is what the mouse experiment did.” The experiment changed gene dose, not reaction or diffusion rates; reading the dose as a change of wavelength is the authors’ modelling argument. The step said the experiment changed the rates.

Claim 35 · checked 24 September 2026 · AI-assisted audit

Position is also told, not only computed

Claim: Position is also told, not only computed

Kind
What the field holds. The settled view of a field, as a review, a consensus statement or a reference work gives it. Not one study.
Review
Source checked. The cited passage was read, and it says this.

Later work looked for

Europe PMC, 2019 on, reviews on "positional information": later reviews (for example on tissue scaling, 2019, and on its information content, 2021) develop the idea; nothing that retracts it.

Claim 36 · checked 24 September 2026 · AI-assisted audit

Claim: Alongside self-organisation, cells read gradients of signalling molecules to know roughly where they are, and switch on different genes at different concentrations.

Kind
What the field holds. The settled view of a field, as a review, a consensus statement or a reference work gives it. Not one study.
Review
Source checked. The cited passage was read, and it says this.

  • Supports

    Positional information and reaction-diffusion: two big ideas in developmental biology combinesection on Wolpert and positional information

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Research in animals · Review of the field

    The source reads: such proof was forthcoming in the discovery of the Bicoid gradient in Drosophila (Fig. 2A) and the demonstration that in Xenopus a TGFβ superfamily protein growth factor could trigger different cell fates separated by concentration thresholds

Later work looked for

Europe PMC, 2019 on, reviews on "positional information": the concept is developed, not retracted.

Claim 37 · checked 24 September 2026 · AI-assisted audit

Claim: Wolpert named that positional information in 1969,

Kind
Historical claim. A statement about the past that historical evidence can test.
Review
Source checked. The cited passage was read, and it says this.

What this does not establish

Green and Sharpe note that the idea of gradients is much older and that others, Lawrence among them, set out similar ideas at the same time.

Claim 38 · checked 24 September 2026 · AI-assisted audit

Claim: and it has been the other half of the subject since.

Kind
What scholars argue. A report of what specialists argue, or where they disagree.
Review
Source checked. The cited passage was read, and it says this.

Claim 39 · checked 24 September 2026 · AI-assisted audit

Claim: Both mechanisms operate,

Kind
What the field holds. The settled view of a field, as a review, a consensus statement or a reference work gives it. Not one study.
Review
Source checked. The cited passage was read, and it says this.

Positional information has molecular proof in the fly and frog (claim 37); self-organisation has molecular examples in the palate and the limb.

  • Supports

    Positional information and reaction-diffusion: two big ideas in developmental biology combinesections on positional information and on the revival of Turing’s idea

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Research in animals · Review of the field

    The source reads: This deficit has only relatively recently begun to be corrected with clear examples of RD systems in which both an activator and an inhibitor with the necessary interactions have been identified

Later work looked for

Europe PMC, 2019 on, reviews on Turing and reaction-diffusion systems in development: Landge 2020 says how common the mechanism is remains unclear, Vittadello 2021 calls its developmental role firmly established; both added to the page.

Claim 40 · checked 24 September 2026 · AI-assisted audit

Claim: and Green and Sharpe propose three distinct ways they could work together, which they present as a hypothesis.

Kind
What scholars argue. A report of what specialists argue, or where they disagree.
Review
Source checked. The cited passage was read, and it says this.

  • Supports

    Positional information and reaction-diffusion: two big ideas in developmental biology combineabstract; Perspectives

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Review of the field

    The source reads: propose a scheme of three distinct ways in which these two ideas work together to shape biological form ... the ideas presented here should be taken as a conceptual framework and a hypothesis, the full confirmation of which will depend on further discoveries over the coming years

Corrected

24 September 2026. Previously: “and Green and Sharpe set out three distinct ways they work together.” The authors call their three modes "a conceptual framework and a hypothesis" whose confirmation depends on future work.

Claim 41 · checked 24 September 2026 · AI-assisted audit

Claim: In the limb, the leading model is a self-organising digit network modulated by morphogen gradients.

Kind
What a model says. What a theory or model predicts or describes, which is not the same as what has been observed.
Review
Partly checked. Only part of the source could be read. What was not read is listed.

  • Supports

    Digit patterning is controlled by a Bmp-Sox9-Wnt Turing network modulated by morphogen gradientsabstract

    Cited · Link answered, 19 October 2026 · Abstract only, 24 September 2026 · Research in animals · Experiment

    The source reads: We develop a realistic two-dimensional simulation of digit patterning and show that this network, when modulated by morphogen gradients, recapitulates the expression patterns of Sox9 in the wild type and in perturbation experiments.

  • Supports

    Positional information and reaction-diffusion: two big ideas in developmental biology combineMode 2: RD acting in parallel with PI; Mode 3: RD acting downstream of PI

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Research in animals · Review of the field

    The source reads: The limb bud develops a periodic gene expression pattern prefiguring the digits, for which evidence points overwhelmingly to a Turing mechanism ... It has been proposed that a known distal-to-proximal gradient of Fgf signalling modulates not only limb outgrowth but also the wavelength of digit periodicity.

What this does not establish

A model that reproduces gene expression in mouse limbs; the Raspopovic paper was read only as its abstract. Claim 50 reports a later caution about what such fits show.

Corrected

24 September 2026. Previously: “In the limb, the digit network behaves as a self-organising system being modulated by morphogen gradients.” The source is a model that reproduces the expression pattern; the page stated the model’s description as the limb’s behaviour.

Claim 42 · checked 24 September 2026 · AI-assisted audit

What is doing it

Claim: What is doing it

Kind
Framing. Signposting. It asserts nothing a source could check.

Claim: The fingers may be stripes, with genes setting their spacing.

Kind
Hypothesis. A proposed explanation, not an established one.
Review
Source checked. The cited passage was read, and it says this.

What this does not establish

Argued from mouse genetics and modelling. The genes modulate the spacing in the model; a gradient of Fgf is also proposed to.

Corrected

24 September 2026. Previously: “The fingers are stripes, and the genes are setting their spacing.” The interlude stated as fact what the page itself, two paragraphs earlier, says the paper argues for rather than demonstrates.

Claim 44 · checked 24 September 2026 · AI-assisted audit

Which molecules do it

Claim: Which molecules do it

Kind
Framing. Signposting. It asserts nothing a source could check.

Claim: For most Turing-like patterns proposed in animals, the interacting molecules are candidates rather than demonstrations: hair follicles and feather buds alone have several rival proposals.

Kind
What scholars argue. A report of what specialists argue, or where they disagree.
Review
Source checked. The cited passage was read, and it says this.

  • Supports

    Positional information and reaction-diffusion: two big ideas in developmental biology combinesection on the revival of Turing’s idea

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Research in animals · Review of the field

    The source reads: the distribution of the thousands of hair follicles or feather buds in the skin of mammals or birds. Various proposals for the diffusible activator and inhibitor have been made in each case

  • Supports

    Pattern formation mechanisms of self-organizing reaction-diffusion systemsIntroduction

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Review of the field

    The source reads: it remains unclear how commonly the principles of RD systems are actually realized in living systems. Qualitative similarities between in silico RD patterns and in vivo patterns are generally not sufficient to conclude the involvement of an RD mechanism

  • Supports

    Positional information and reaction-diffusion: two big ideas in developmental biology combinesection on the revival of Turing’s idea

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Review of the field

    The source reads: the proof that a Turing mechanism was the actual basis of these patterns was lacking ... This deficit has only relatively recently begun to be corrected with clear examples of RD systems in which both an activator and an inhibitor with the necessary interactions have been identified

    The share is not counted in either source: "most" rests on Green and Sharpe describing identified molecular cases as a recent minority beginning to correct a general lack of proof.

Later work looked for

Europe PMC, 2019 on, reviews on Turing and reaction-diffusion systems in development: Landge 2020 says how common the mechanism is remains unclear, Vittadello 2021 calls its developmental role firmly established; both added to the page.

Corrected

24 September 2026. Previously: “For most Turing-like patterns in animals the interacting signals have not been identified.” Molecules have been proposed for many of these patterns; what is missing is proof. Green and Sharpe list several competing pairs for hair follicles and feather buds.

Claim 46 · checked 24 September 2026 · AI-assisted audit

Claim: Digits are among the cases that have gone furthest:

Kind
What scholars argue. A report of what specialists argue, or where they disagree.
Review
Source checked. The cited passage was read, and it says this.

  • Supports

    Positional information and reaction-diffusion: two big ideas in developmental biology combinesection on Turing and reaction-diffusion

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Research in animals · Review of the field

    The source reads: clear examples of RD systems in which both an activator and an inhibitor with the necessary interactions have been identified ... the patterning of palatal ridges (Economou et al., 2012) or digits (Raspopovic et al., 2014) during mouse embryogenesis

Corrected

24 September 2026. Previously: “Digits are the case that has gone furthest:” Green and Sharpe give the palatal ridges of the mouse, patterned by Fgf and Shh, as a molecular case alongside the digits.

Claim 47 · checked 24 September 2026 · AI-assisted audit

Claim: a 2014 paper proposes a network of Bmp, Sox9 and Wnt, arrived at by combining experiments with a two-dimensional simulation that reproduces Sox9 expression in normal limbs and in perturbed ones.

Kind
Experimental result. What an experiment or trial found, under its own conditions. A result in animals, cells or a simulation is not a result in people.
Review
Partly checked. Only part of the source could be read. What was not read is listed.

  • Supports

    Digit patterning is controlled by a Bmp-Sox9-Wnt Turing network modulated by morphogen gradientsabstract

    Cited · Link answered, 19 October 2026 · Abstract only, 24 September 2026 · Research in animals · Experiment

    The source reads: a Turing network implemented by Bmp, Sox9, and Wnt drives digit specification. We develop a realistic two-dimensional simulation of digit patterning ... recapitulates the expression patterns of Sox9 in the wild type and in perturbation experiments.

  • Context

    Pattern formation mechanisms of self-organizing reaction-diffusion systemssection on digit patterning

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Research in animals · Review of the field

    The source reads: a three-node Turing network was proposed to underlie digit patterning, in which BMP and Wnt are diffusible nodes and Sox9 is a non-diffusible node

What this does not establish

In mouse limb buds. The paper was read only as its abstract; the experiments and the simulation were not.

Later work looked for

Europe PMC, 2013 on, "Hox digit Turing wavelength" and "Sox9 Turing digit": later work extends the account (Marcon 2016 five-node network, Onimaru 2016 in catshark fins) and a 2015 review of distinguishing periodic-patterning models; nothing found that overturns the result.

Claim 48 · checked 24 September 2026 · AI-assisted audit

Claim: A model that fits a pattern is much easier to produce than a demonstration that particular molecules produce it.

Kind
What scholars argue. A report of what specialists argue, or where they disagree.
Review
Source checked. The cited passage was read, and it says this.

Corrected

24 September 2026. Previously: “A model that fits the pattern is much easier to produce than a demonstration that a particular set of molecules produces it, which is the state of the field.” "The state of the field" was the page’s own verdict on a field whose reviewers disagree about how settled it is; the disagreement is now reported with who holds each side.

Claim 49 · checked 24 September 2026 · AI-assisted audit

Claim: A 2020 review holds that resemblance between simulated and real patterns is not enough, and that how often living systems use the mechanism remains unclear;

Kind
What scholars argue. A report of what specialists argue, or where they disagree.
Review
Source checked. The cited passage was read, and it says this.

  • Supports

    Pattern formation mechanisms of self-organizing reaction-diffusion systemsIntroduction

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Review of the field

    The source reads: it remains unclear how commonly the principles of RD systems are actually realized in living systems. Qualitative similarities between in silico RD patterns and in vivo patterns are generally not sufficient to conclude the involvement of an RD mechanism

Later work looked for

Europe PMC, 2019 on, reviews on Turing and reaction-diffusion systems in development: Landge 2020 says how common the mechanism is remains unclear, Vittadello 2021 calls its developmental role firmly established; both added to the page.

Corrected

24 September 2026. Previously: “” Added from the currency search, to report where reviewers of the field stand, in place of the page’s own verdict.

Claim 50 · checked 24 September 2026 · AI-assisted audit

Claim: a 2021 review calls its role in development firmly established.

Kind
What scholars argue. A report of what specialists argue, or where they disagree.
Review
Source checked. The cited passage was read, and it says this.

The two reviews are not strictly opposed: one asks how common the mechanism is, the other whether it has a role at all.

  • Supports

    Turing pattern design principles and their robustnessabstract

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Review of the field

    The source reads: For a long time, their biological significance was sometimes disputed but there is now ample evidence for their involvement in processes ranging from skin pigmentation to digit and limb formation. While their role in developmental biology is now firmly established

Later work looked for

Europe PMC, 2019 on, reviews on Turing and reaction-diffusion systems in development: Landge 2020 says how common the mechanism is remains unclear, Vittadello 2021 calls its developmental role firmly established; both added to the page.

Claim 51 · checked 24 September 2026 · AI-assisted audit

Claim: The digit network has since grown from three components to five, and when the 2020 review was written some of the added interactions were still untested.

Kind
What scholars argue. A report of what specialists argue, or where they disagree.
Review
Source checked. The cited passage was read, and it says this.

  • Supports

    Pattern formation mechanisms of self-organizing reaction-diffusion systemssection on digit patterning

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Research in animals · Review of the field

    The source reads: The three-node Turing network was subsequently extended to a five-node network (Fig. 5c) using the software RDNets (Marcon et al., 2016). ... Additional negative feedbacks between Sox9, BMP and Wnt signaling were postulated (Marcon et al., 2016), but these interactions remain to be tested experimentally.

Later work looked for

Europe PMC, 2016 on, "Sox9 Turing digit": no experimental test of the postulated feedbacks found; the sentence is dated to the review.

Corrected

24 September 2026. Previously: “” Added from Landge and others 2020, which records the revision of the digit model.

Claim 52 · checked 24 September 2026 · AI-assisted audit

How it is so reliable

Claim: How it is so reliable

Kind
Framing. Signposting. It asserts nothing a source could check.

Claim: Early analyses found Turing systems sensitive to noise and to their starting conditions,

Kind
What scholars argue. A report of what specialists argue, or where they disagree.
Review
Source checked. The cited passage was read, and it says this.

Corrected

24 September 2026. Previously: “Self-organising systems are sensitive to their starting conditions, and development is not: human hands have five fingers with very high reliability despite variation in everything.” Sensitivity was what early analyses concluded, not a property of all self-organising systems; Gierer and Meinhardt, and later network analyses, found designs that regulate. "Despite variation in everything" had no source.

Claim 55 · checked 24 September 2026 · AI-assisted audit

Claim: and development is not: digits form in the same stereotyped pattern in individual after individual.

Kind
Observation. Something measured or seen, as the named source reports it.
Review
Source checked. The cited passage was read, and it says this.

  • Supports

    Positional information and reaction-diffusion: two big ideas in developmental biology combinesection on the revival of Turing’s idea

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Research in animals · Review of the field

    The source reads: two recent proposals have been made for periodic structures that show a reliably stereotypical pattern across all individuals within a species

    The two are the palatal ridges and the digits.

What this does not establish

Reliable is not invariant: extra digits do occur, which is how the mouse mutants of claim 19 are recognised.

Later work looked for

An anatomical regularity; not a finding later work revises.

Claim 56 · checked 24 September 2026 · AI-assisted audit

Claim: What makes the outcome robust is an open question,

Kind
Open question. Something the page says is not known.
Review
Presented as open. The page says this is unresolved, and the review found that it is.

Corrected

24 September 2026. Previously: “What makes the outcome robust to noise, temperature and genetic variation is an active question,” No cited source discusses temperature or genetic variation; the claim is narrowed to robustness.

Claim 57 · checked 24 September 2026 · AI-assisted audit

Claim: and it is the part that any engineering account of development has to answer.

Kind
This page’s reading. A judgement the page makes from the evidence. Others read it differently.
Review
A judgement, not a fact. Reviewed for whether it is fairly put and follows from the checked claims. No source can confirm it.

The page’s judgement of why robustness matters; not a claim a source could confirm.

Claim 58 · checked 24 September 2026 · AI-assisted audit

Claim: Later modelling has found network designs that form patterns across a wide range of their parameters,

Kind
What scholars argue. A report of what specialists argue, or where they disagree.
Review
Source checked. The cited passage was read, and it says this.

Landge and others define a robust network as one that forms Turing patterns for a wide range of reaction-diffusion parameters.

  • Supports

    Pattern formation mechanisms of self-organizing reaction-diffusion systemssection on robust Turing networks

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · A simulation · Review of the field

    The source reads: It has been thought that Turing networks require intricate fine-tuning of the reaction and diffusion parameters to yield stable patterns ... recent insights obtained from the analysis of realistic multi-component RD systems enable the design and discovery of robust Turing networks ... Turing patterns for a wide range of reaction-diffusion parameters

What this does not establish

Computational screens of model networks, whose generality, the review notes, may be limited by the kinetic functions chosen.

Later work looked for

Europe PMC, 2015 on, "Turing robust": Scholes 2019 and Vittadello 2021 continue the analysis; the question is still being worked on.

Corrected

24 September 2026. Previously: “” Added so the page does not present the early finding of sensitivity as the current state of the modelling.

Claim 59 · checked 24 September 2026 · AI-assisted audit

Claim: which answers part of the old objection without showing that development uses them.

Kind
This page’s reading. A judgement the page makes from the evidence. Others read it differently.
Review
A judgement, not a fact. Reviewed for whether it is fairly put and follows from the checked claims. No source can confirm it.

Follows from claims 55 and 59, and from the same review’s statement that how commonly the mechanism is realised in living systems is unclear.

  • Context

    Pattern formation mechanisms of self-organizing reaction-diffusion systemsIntroduction

    Cited · Link answered, 19 October 2026 · Read in full, 24 September 2026 · Theory · Review of the field

    The source reads: it remains unclear how commonly the principles of RD systems are actually realized in living systems. Qualitative similarities between in silico RD patterns and in vivo patterns are generally not sufficient to conclude the involvement of an RD mechanism

Claim 60 · checked 24 September 2026 · AI-assisted audit

Claim: The 2014 digit model gets its reproducibility from a combination of growth, morphogen gradients and the self-organising network.

Kind
What a model says. What a theory or model predicts or describes, which is not the same as what has been observed.
Review
Partly checked. Only part of the source could be read. What was not read is listed.

What this does not establish

What the model shows, in mouse limb buds; the paper was read only as its abstract, so how robustness was tested was not read.

Corrected

24 September 2026. Previously: “The 2014 digit model gets its reproducibility from a combination: growth, morphogen gradients and the self-organising network together, not the network on its own.” The abstract says the combination can achieve robust and reproducible patterning; it does not say the network alone cannot, and the body was not read.

Claim 61 · checked 24 September 2026 · AI-assisted audit

What was read