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Evolution and evolvability  ·  Article

Discontinuous variation

Discontinuous variation is variation in which forms fall into separate groups instead of grading into one another. Bateson (1894) set it apart for study and divided it into meristic and substantive kinds2. The idea of a gap recurs in work on heredity, perception, muscle, nerves and mind134.

Earliest held
1890, James, W.
Most discussed in
Materials for the Study of Variation Treated…, 1894
In the library
325 passages in 22 works
Rewritten
2026-10-03
18501875190019251950197520002025James, W., 18901Bateson, W., 18942Verworn, M., 18993Bayliss, W. M., 19154Loeb, J., 19165Thompson, D. A. W., 19926Thompson, D. A. W., 19927Levin M, 20228Fields C, Levin M, 20229
01

Bateson and the earwig

In Materials for the Study of Variation (1894), Bateson proposed limiting attention to discontinuous variations. He said they may be meristic or substantive, and he took the meristic group first2. Thompson, in On Growth and Form, recalled Bateson's paper on earwigs. Among many males from one locality, the forceps fell into two groups, large or small, with very few intermediates6. Thompson argued that these differences were purely a matter of magnitude. He judged the curves comparable to those for older and younger fish7. Loeb (1916) credited de Vries with showing that fluctuating variations are not hereditary, while sports or mutations are inherited5.

02

Gaps in perception and tissue

James (1890) applied the term to perception. For separate clicks to be heard as discontinuous, three or four must be spaced farther apart than two. Series at one interval were often judged to contain fewer clicks than they did1. Verworn (1899) described sustained contractions under nervous influence as discontinuous. He held that they are built from many single contractions in rapid succession, as in artificial tetanus3. Bayliss (1915) took the limit of degeneration in a cut nerve fibre as the clearest proof that neurones are structurally discontinuous. He added that physiological continuity must still exist4.

03

Continuity as the default

Recent work by Levin treats the question as open. Levin (2022) says it is unresolved whether upgrades to cognition produce truly discontinuous jumps in consciousness. The TAME framework allows sharp phase transitions but takes continuity as its null hypothesis8. Levin suggested that future brain-computer interfaces might let a subject judge whether such a change had occurred8. Fields and Levin (2022) place simple systems that roll down a hill on one spectrum with psychological systems. They argue this explains how complex minds arise without magical discontinuities in evolution or development9.

SourcesEach quotation was checked word for word against the passage it opens.
  1. When two are easily distinguished, three or four separated by the same interval . . . are often confidently pronounced to be two or three respectively.James, W., 1890 · The Principles of Psychology, Vols. 1-2 · open at passage 1446
  2. Discontinuous Variations may belong to the Meristic Group or to the Substantive, but it is to the former that attention will first be directed.Bateson, W., 1894 · Materials for the Study of Variation Treated with Especial Regard to… · open at passage 106
  3. All continued contractions that are performed in the human body under nervous influence are, like tetanus artificially produced, discontinuous phenomena composed of many single contractions following one another in rapid succession.Verworn, M., 1899 · General Physiology: An Outline of the Science of Life · open at passage 1075
  4. Perhaps the clearest proof of the structural discontinuity of the individual neurones is afforded by the fact that the degeneration which takes place in a nerve fibreBayliss, W. M., 1915 · Principles of General Physiology · open at passage 2051
  5. fluctuating variations are not hereditary and hence could not have played the r61e assigned to them by Darwin, while discontinuous variations as they appear in the so-calledLoeb, J., 1916 · The Organism as a Whole, from a Physicochemical Viewpoint · open at passage 532
  6. In a very well-known paper, Bateson shewed that, among a large number of earwigs, collected in a particular locality, the males fell into two groups, characterised by large or by small tail-forceps, with very few instances of intermediate magnitude.Thompson, D. A. W., 1992 · On Growth and Form · open at passage 253
  7. we cannot help seeing that the discontinuous distributions of magnitude represented by his earwigs’ tails are just such as are illustrated by the magnitudes of the older and younger fishThompson, D. A. W., 1992 · On Growth and Form · open at passage 255
  8. The TAME framework is not incompatible with novel discoveries about sharp phase transitions, but it takes the null hypothesis to be continuityLevin M, 2022 · Technological Approach to Mind Everywhere: An Experimentally-Grounded Framework… · open at passage 111
  9. how complex minds emerge from “just physics” without magical discontinuities in evolution or developmentFields C, Levin M, 2022 · Competency in Navigating Arbitrary Spaces as an Invariant for Analyzing… · open at passage 58
Linked ideas
Thompson reads Bateson's discontinuous earwig distributions as differences of magnitude tied to growth over time, a different reading of the same data.
Basal cognitionin tension with
Levin and Fields treat cognition as a continuum and take continuity as the null hypothesis, against sharp discontinuous jumps.
Fields and Levin place simple systems that roll down a hill and cognitive systems on one spectrum of agency, without discontinuities.
Levin asks whether cognitive upgrades produce truly discontinuous jumps in consciousness, which bears on where any criterion of mind could be drawn.
Evolvabilityrelated to
Loeb's account of heritable mutations versus non-heritable fluctuations bears on how variation can feed evolution.
Gap junctionsrelated to
Bayliss's structural discontinuity of neurones concerns contact between cells, with physiological continuity across it.
Where it is discussedPassages matching discontinuous variation, discontinuity, meristic, homoeosis
1894Materials for the Study of Variation Treated with Especial Regard to… · Bateson, W.248
1890The Principles of Psychology, Vols. 1-2 · James, W.17
1906Plant Response as a Means of Physiological Investigation · Bose, J. C.11
1926Muscular Activity · Hill, A. V.6
1908The Science and Philosophy of the Organism · Driesch, H.6
1992On Growth and Form · Thompson, D. A. W.5
1923Protoplasmic Action and Nervous Action · Lillie, R. S.5
1925Elements of Physical Biology · Lotka, A. J.4
1899General Physiology: An Outline of the Science of Life · Verworn, M.3
1922Injury, Recovery and Death in Relation to Conductivity and Permeability · Osterhout, W. J. V.3