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Minds of small things  ·  Article

Behaviour of single cells

Single-celled organisms such as Amoeba, Paramecium and Stentor move, feed, regenerate and respond to stimuli without a nervous system. Authors from Binet onward have described these acts, and some have called them intelligent.9 The same animals later served as test cases for whether a single cell can learn, and the evidence is disputed.67

Earliest held
1888, Binet, A.
Most discussed in
Behavior of the Lower Organisms, 1906
In the library
882 passages in 42 works
Rewritten
2026-10-06
18501875190019251950197520002025Binet, A., 18881Verworn, M., 18992Morgan, T. H., 19013Driesch, H., 19084Child, C. M., 19155Fernando CT, Liekens AM, Bingle LE…, 20096Gershman SJ, Balbi PE, Gallistel CR…, 20217Gershman SJ, Balbi PE, Gallistel CR…, 20218Trewavas A, 20259
01

Early observations

Binet (1888) tried to explain how an amoeba makes pseudopodia. He held that protoplasmic masses, especially the amoeba, have an elastic outer layer and a liquid interior.1 Morgan (1901) reviewed work on cut ciliates. Nussbaum cut Oxytricha and Gastrostyla, and the pieces holding part of the nucleus regenerated a smaller whole organism that could reproduce.2 Pieces without nucleus did not regenerate, though they moved about for up to two days before disintegrating.2 Verworn (1899) reported that Paramecium swims toward the kathode in an electric current. He added that most ciliate infusorians behave this way, and that Amoeba limax streams toward the kathode as well.3

02

Random movement and gradients

Driesch (1908) treated motion at random as the most elemental motor act. He separated two classes of random movement and placed all amoebae in the first. In his account any stimulus may be followed by any movement in any possible direction.4 Child (1915) looked at single cells from another side. He described a gradient along the apico-basal axis and showed Stentor coeruleus disintegrating in order along that axis, in a series of figures.5

03

Claims of learning

Fernando and colleagues (2009) reported that Hennessey (1979) trained Paramecium caudatum to avoid a vibration paired with electric shock.6 They noted that sensitization and pseudo-conditioning were not ruled out.6 Gershman and colleagues (2021) reviewed older tube-escape work. Paramecia placed in capillary tubes became faster at reversing, and French (1940) found faster downward escape.7 Hinkle and Wood (1994) found Stentor also swam downward when escape lay at the top, so tube orientation may confound the result.7 Gershman and colleagues also say Jennings' Stentor work was discredited because a different species was used, and that work with the correct species vindicated him.8

04

Later readings

Trewavas (2025) cites Binet as having concluded that protozoa were intelligent organisms.9 He says Jennings (1906) reached the same conclusion.9 Gershman and colleagues take a more cautious line. They argue that the reception of Jennings' work shows a habit of discounting complex behaviour in single cells. They also say learning must be studied in the ecological context of each species, since what one Stentor species learns may not apply to another.8

SourcesEach quotation was checked word for word against the passage it opens.
  1. All protoplasmic masses, and especially the amoeba, consist of two parts, an enveloping membrane or ectosarc, viscous and elastic, and the central liquid contents holding granules in suspension.Binet, A., 1888 · The Psychic Life of Micro-organisms: A Study in Experimental Psychology · open at passage 32
  2. Like Paramcecium, the majority of the ciliate Infusoria are kathodically galvanotactic.Verworn, M., 1899 · General Physiology: An Outline of the Science of Life · open at passage 1155
  3. Those pieces that contained a nucleus quickly regenerated a new whole organism of smaller size, that had the power of further reproductionMorgan, T. H., 1901 · Regeneration · open at passage 162
  4. All Amoebae are a good instance of the first type : any stimulation may be followed by every possible movement in every geometrically possible directionDriesch, H., 1908 · The Science and Philosophy of the Organism · open at passage 48
  5. Figs. 3-7 show the course of death and disintegration along the axis in Stentor coendeiis, one of the common infusoria.Child, C. M., 1915 · Individuality in Organisms · open at passage 99
  6. Hennessey (1979) showed that the single-celled ciliate Paramecium caudatum might possibly be capable of being classically conditioned.Fernando CT, Liekens AM, Bingle LE, Beck C, Lenser T…, 2009 · Molecular circuits for associative learning in single-celled organisms · open at passage 3
  7. Hinkle and Wood, 1994, using Stentor as their subjects, presented evidence that the learning effect may be confounded with the orientation of the tubeGershman SJ, Balbi PE, Gallistel CR, Gunawardena J, 2021 · Reconsidering the evidence for learning in single cells · open at passage 16
  8. recent experimental work with the correct species has vindicated Jennings (Dexter et al., 2019)Gershman SJ, Balbi PE, Gallistel CR, Gunawardena J, 2021 · Reconsidering the evidence for learning in single cells · open at passage 14
  9. authored a textbook on protozoan behaviour and concluded that they were intelligent organisms.Trewavas A, 2025 · Plant intelligence dux: a comprehensive rebuttal of Kingsland and Taiz · open at passage 6
Linked ideas
Regenerationrelated to
Morgan and Verworn report that nucleated pieces of Stentor and other protozoa regenerate into whole cells.
Child describes a susceptibility gradient along the axis of a single Stentor cell, using cyanide disintegration.
Fábregas-Tejeda and Sims cite habituation in Stentor as learning that needs no neurons, a memory case outside nervous systems.
Levin (2025) uses the amoeba's small cognitive light cone to frame cancer as cells reverting to unicellular goals.
Manicka and Levin move from single-cell memory and decisions to tissues detecting the difference from a correct form.
Trial and errorrelated to
Jennings builds the idea from the movements of Paramecium and Amoeba, and compares how effective their differing movements are at escaping unfavourable conditions.
Tropismrelated to
Loeb offers tropisms as elements for a mechanistic account of animal behaviour, the same ground Jennings's trial-and-error work covers.
Jennings's work on lower organisms supplies the behavioural evidence, while he argues it cannot decide whether consciousness is present.
Binet and Jennings describe infusorian food habits that change with the medium, an early case of behavioural plasticity.
Basal cognitionrelated to
Single cells and other aneural organisms are cited as showing memory, prediction and learning without a nervous system.
Collective intelligence of cellsprecursor of / follows
Levin says cells derive from unicellular ancestors with rich behavioral repertoires; Verworn and Jennings describe swarm-spore responses to light.
Lotka's amoeba is his doubtful case: purposive or mechanistic cannot be settled while its working is unknown.
Jennings's infusoria show reactions to chemicals that vary with the past and present conditions of the individual.
Galvanotaxispart of / contains
Galvanotaxis is one single-cell response: Paramecium, Polytoma and Pleuronema swim toward or away from the kathode, and Amoeba contracts at the anode. Driesch calls it real taxis amongst Infusoria.
Metabolism and cell fateprecursor of / follows
Jennings made metabolic state the main determinant of reactions in simple organisms, an early form of the idea.
Loeb applies the same heliotropism experiments to Volvox, and Evangelidis et al. report gravisensitivity and geotropism in Physarum.
Physarum is a single cell whose foraging and choices are described in the held passages, so it is a unicellular case.
Physical forces and formprecursor of / follows
Verworn's surface-tension picture of amoeboid motion is an early physical account of single-cell movement.
Resting membrane potentialprecursor of / follows
Resting membrane potential was first measured inside a single cell in Paramecium.
Lyon describes bacteria judging signals against their own internal milieu.
Binet and Jennings tie the movements of bacteria and infusorians to light and to oxygen produced by chlorophyll.
Jennings's work on Amoeba and rolling movement bears on whether unicells show orientation at all.
Early and modern arguments about learning in single cells, the other main non-neural test case.
Bacterial memory is one aspect of the wider question of how single cells respond to their surroundings.
Jennings's work on Paramecia and the early debate on single-cell behaviour come before the molecular account of bacterial steering.
Behaviour of single cells is the evidence base the nanobrain proposal draws on.
Where it is discussedPassages matching Paramecium, infusoria, amoeba, Stentor
1906Behavior of the Lower Organisms · Jennings, H. S.398
1899General Physiology: An Outline of the Science of Life · Verworn, M.158
1888The Psychic Life of Micro-organisms: A Study in Experimental Psychology · Binet, A.75
1896The Cell in Development and Inheritance · Wilson, E. B.30
1908The Animal Mind: A Textbook of Comparative Psychology · Washburn, M. F.30
1992On Growth and Form · Thompson, D. A. W.30
1915Principles of General Physiology · Bayliss, W. M.19
1908The Science and Philosophy of the Organism · Driesch, H.18
1901Regeneration · Morgan, T. H.17
1930The History of Biological Theories · Rádl, E.16