BioelectricaAlterspan Labs
Evolution and evolvability  ·  Article

Germ-plasm theory and chromosome individuality

Germ-plasm theory held that a special hereditary substance, carried by the reproductive cells, holds the characteristics of the species. Weismann placed it in the chromosomes, which he read as groups of units called ids.12 The theory set the terms for later arguments over whether bodily experience can reach heredity. Those arguments return in current work on cellular memory.79

Earliest held
1890, James, W.
Most discussed in
The Cell in Development and Inheritance, 1896
In the library
228 passages in 20 works
Rewritten
2026-10-06
18501875190019251950197520002025Wilson, E. B., 18961Wilson, E. B., 18962Loeb, J., 19163Child, C. M., 19244Rádl, E., 19305Rádl, E., 19306Neuhof M, Levin M, Rechavi O, 20167Silver BB, Nelson CM, 20188Levin M, 20239
01

Ids and chromosomes

Wilson's 1896 glossary records the vocabulary. Nägeli's idioplasm, a substance now generally identified with chromatin, was taken to carry the characteristics of the species by its inherent organization, and Wilson called it equivalent to Weismann's germ-plasm.1 Wilson also reports that the ids were assumed to differ slightly, in step with individual variation, so that each chromosome was a distinct group of germ-plasms. Fertilization mixed ids to make new combinations. Because union of two germ-nuclei doubles their number, Weismann held that a periodic reduction must occur.2

02

Reduction division

Weismann assumed the ids lay in a linear series along the chromosome. From this he predicted two kinds of mitosis, one an ordinary longitudinal splitting and one a reduction.2 Loeb, in 1916, set out the account he credited to Sutton. Every cell carries two homologous sets of chromosomes, one paternal and one maternal. Egg and sperm each lose one set in the reduction division. The lost set mixes maternal and paternal chromosomes without preference. According to Loeb, Sutton took this to be the basis of Mendelian heredity.3

03

Sorting and the barrier

Child, in 1924, described the Roux-Weismann theory of qualitative nuclear division. In it development is a sorting process, and cells differ by the determinants assigned to them. He wrote that observation and experiment had forced its abandonment. Morgan's view that each cell inherits the whole germ plasm had replaced it.4 Rádl, in 1930, described a second consequence. Weismann inferred that characters acquired in a lifetime die with the individual, because they change only the somatoplasm.5 Rádl disputed the basis of this. He judged that the denial rested on an unproven difference between germ-plasm and somatoplasm, not on new insight into natural processes.6

04

The barrier in recent work

Silver and Nelson (2018) state the Weismann barrier as a postulate that information passes from germ cells to somatic cells and not back. They note that some mechanisms may violate it. One example is incomplete erasure of DNA methylation during germ cell development, which may carry changes from soma to germ cells.8 Neuhof, Levin and Rechavi (2016) ask whether memory-encoding alterations could breach the barrier and persist across generations. They also raise the question for asexual organisms.7 Levin (2023) argues the obstacle is not breaching the barrier. It is the unsolvable inverse problem of deciding what to encode to produce a desired anatomy.9

SourcesEach quotation was checked word for word against the passage it opens.
  1. equivalent to the germ- plasm of Weismann. The substance, now generally identified with chromatin, which by its inherent organization involves the characteristics of the species.Wilson, E. B., 1896 · The Cell in Development and Inheritance · open at passage 1048
  2. Since, however, their number, like that of the chromosomes which they form, is doubled by the union of two germ-nuclei, an infinite complexity of the chromatin would soon arise did not a periodic reduction occur.Wilson, E. B., 1896 · The Cell in Development and Inheritance · open at passage 576
  3. each loses one set of homologous chromosomes in the sccalled reduction division, but the lost set is made up indiscriminately of maternal as well as paternal chromosomesLoeb, J., 1916 · The Organism as a Whole, from a Physicochemical Viewpoint · open at passage 373
  4. According to the Roux-Weismann theory of qualitative nuclear division, development is itself a distributing or sorting process in which the various determinants are assigned to their proper places.Child, C. M., 1924 · Physiological Foundations of Behavior · open at passage 250
  5. he inferred that characters acquired during the life time of the individual must die with that individual, since they merely represent a change in the body, in the somatoplasm.Rádl, E., 1930 · The History of Biological Theories · open at passage 647
  6. Weismann's denial of the inheritance of acquired characters was not due to any new insight into natural processes.Rádl, E., 1930 · The History of Biological Theories · open at passage 648
  7. could parentally-produced alterations that encode biological memory breach Weismann's barrier and persist across generations?Neuhof M, Levin M, Rechavi O, 2016 · Vertically- and horizontally-transmitted memories - the fading boundaries… · open at passage 9
  8. incomplete erasure of DNA methylation patterns during germ cell development may result in the transfer of genetic modifications from the soma to germ cellsSilver BB, Nelson CM, 2018 · The Bioelectric Code: Reprogramming Cancer and Aging From the Interface of… · open at passage 37
  9. the inverse problem [20] is in general unsolvable: determining which protein sequences must be encoded to produce an arbitrary, desired large-scale anatomical form.Levin M, 2023 · Darwin's agential materials: evolutionary implications of multiscale competency… · open at passage 7
Linked ideas
Both concern where hereditary determinants sit and how cells come to differ. Child set sorting of determinants against the view that each cell holds the whole germ plasm.
Loeb objected that Weismann used natural selection to explain forms such as roots and polyps, and argued this would not help physiological morphology.
Neuhof and colleagues raise the barrier question for planaria, where new organisms form from neoblasts without a segregated germline.
Silver and Nelson use somatic versus germline p53 mutations to show what the barrier does and does not forbid, in a bioelectric cancer context.
Evolvabilityrelated to
Levin's 2023 argument on why somatic experience cannot simply be written back into a genome bears on how lineages change.
Regenerationin tension with
Neuhof et al. say planarian regeneration/asymmetric fission evades the Weismann barrier, blurring inheritance and development; Morgan examines Weismann's regeneration views; Child doubts cells' inherited germ plasm explains regional polarity.
Physiologists testing responses experimentally (Loeb's Tubularia/Pennaria regeneration, Child's physico-chemical view) challenge Weismann's corpuscular germ-plasm and selection explanations as neglecting organization and environmental reaction.
Rink notes neoblasts resemble germ cells, though they are not germ cells, and nanos separates the germ line lineage.
Where it is discussedPassages matching germ-plasm, Weismann, ids and determinants, individuality of chromosomes
1896The Cell in Development and Inheritance · Wilson, E. B.59
1930The History of Biological Theories · Rádl, E.47
1901Regeneration · Morgan, T. H.28
1924Physiological Foundations of Behavior · Child, C. M.23
1899General Physiology: An Outline of the Science of Life · Verworn, M.22
2016Vertically- and horizontally-transmitted memories - the fading boundaries… · Neuhof M, Levin M, Rechavi O9
1916The Organism as a Whole, from a Physicochemical Viewpoint · Loeb, J.8
1894Materials for the Study of Variation Treated with Especial Regard to… · Bateson, W.6
1890The Principles of Psychology, Vols. 1-2 · James, W.5
1912The Mechanistic Conception of Life · Loeb, J.4