GENETICS OF NATURAL POPULATIONS. XII. EXPERIMENTAL REPRODUCTION OF SOME OF THE CHANGES CAUSED BY NATURAL SELECTION IN CERTAIN POPULATIONS OF DROSOPHILA PSEUDOOBSCURA

Sewall Wright, Theodosius Dobzhansky · Genetics · 1946 · population-genetics · 10.1093/genetics/31.2.125 · record wright1946-genetics-of-natural-populations-xi
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Where this record's text came from. faceted 2026-08 by reading the locally held text (pdftext); every evidence string verified as an exact substring of that text before merging. The PDF extraction is legible but full of line-break word splits (e.g. 'Dro sophila', 'interpreta tion') and OCR digit errors in the tables; every quote used here was chosen from unbroken runs and machine-checked as an exact substring. The Hovanitz relation is tagged 'contradicts' because the paper introduces that named alternative and then argues from its own dispersal data that migration cannot account for the observed shifts; the quoted sentence is the only one that names the prior work. Claim type is mechanism (frequency change caused by temperature-dependent selection); the paper also carries a strong 'method' component in its mathematical treatment of selection coefficients, which the single-value facet cannot express. 2026-08-14 and 2026-08-25 schema-0.3 passes: every quote verified as an exact substring of the staged text and anchored at merge time; concept terms verified present; every edge endpoint an existing node.
The quality of the text these quotes were cut from. ocr-letter-substitution (GROUNDING COPY): the 1946 scan lost a ligature to a stray symbol in 2 of 13494 whitespace-delimited words in an internal file (0.01%) - 'in~uence' for 'influence', 'hete~ozygotes' for 'heterozygotes'. Sparse enough to be a nuisance rather than a limitation. 48 live quotes cover 11.1% of the body and none carries a damaged token; chance alone predicts 0.22, so that is the expected outcome and not evidence of care.
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Other fields define these differently the same word, defined another way in another discipline
Standard 3 fields · variance 2 fields

Tags on this paper

Every tag the record carries, each linking to every other paper in the corpus that carries it. A tag appears here whether or not its words occur in the article — the spans below are only the ones a sentence in this paper licenses. Of the 3 concept tags on this paper, all 3 are grounded in a quoted sentence.
gene arrangement Standard population cage Heterozygote superiority: because ST/CH heterozygotes are fitter than either homozygote, selection drives the population towards an intermediate equilibrium of chromosome frequencies rather than fixation. The inversions themselves are adaptively neutral, but they lock up different gene complexes that adapt their carriers to different seasonal environments, so seasonal change in the environment shifts their frequencies. Frequency-dependent selection through niche filling: a rare genotype occupies only the niches it is best adapted to and is favoured, but when abundant it must spill into niches it fits poorly and is selected against. selective disadvantage ten-day period temperature factor food regime frequencies of chromosomes gene content chi-squared t-test (Student's) using Students' probabilities for small numbers regression the regression of rate of change on chromosome frequency F-test Fisher's test least squares the method of least squares p-value variance The estimated variance of .:lq for given q experiment
Method, as described: laboratory-experiment

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relation to other workclaim_relationshow this paper stands to another: agrees, contradicts, extends, qualifies
claim typeclaim_typethe shape of the claim: existence, mechanism, method, critique, prediction, null
concept edgeconcept_edgesan asserted relation between two concepts, with the sentence asserting it
conceptconceptsan idea the paper works with, quoted where the paper uses it
content tagcontent_tagsa finding, definition, quantity, statistic or variable named in the paper
controlcontrolsan experiment run to eliminate a rival explanation
limitationlimitationswhat the paper says its evidence cannot support
mechanismmechanismshow the reported effect is said to come about
methodmethodhow the paper produced its evidence
phenomenonphenomenonthe effect or regularity under study
sensesensesa distinct use of a term, quoted where the paper fixes it

The paper

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Every tag on this page

claim_relations 2 · claim_type 1 · concept_edges 1 · concepts 3 · content_tags 31 · controls 1 · limitations 5 · mechanisms 3 · method 1 · phenomenon 1 · senses 3

Relations on this page carry a quotation for the claim. Where a relation was separately evidenced — and so tested against the vocabulary for its type — the row says so; none of 1 relation here carry that mark. The rest are the tagger’s reading of the sentence quoted beside them.

facettagfieldconf.whose words
claim_typemechanism
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claim_typethe paper's words
phenomenonseasonal cycles in chromosomal inversion frequencies
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phenomenonthe paper's words
methodexperiment
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also in: experiment
methodthe paper's words
mechanismsmechanisms
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mechanisms[0]the tagger's words
mechanismsmechanisms
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mechanisms[1]the tagger's words
mechanismsmechanisms
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mechanisms[2]the tagger's words
limitationsAbsence of significant change at the low temperature may reflect too few sampling intervals rather than genuinely constant frequencies.
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what this limits: the low-temperature null: THIS DOES NOT IMPLY THAT THERE WERE NO CHANGES BUT MERELY THAT ANY CHANGES WERE TOO SMALL TO BE DETECTED WITH CONFIDENCE IN THE SMALL NUMBER OF INTERVALS
limitations[0]the tagger's words
limitationsThe data cannot discriminate among the possible selective models (constant selective values, sex-differential selection, frequency-dependent values).
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what this limits: any choice among the selective models: UNFORTUNATELY THE DATA AT HAND DO NOT YIELD A UNIQUE INTERPRETATION
limitations[1]the tagger's words
limitationsThe spring reversal seen in nature was not reproduced and its causes remain unknown.
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what this limits: the correspondence with the wild population: the spring reversal was not reproduced, and THERE ARE IMPORTANT FACTORS YET TO BE DISCOVERED
limitations[2]the tagger's words
limitationsA counting assumption is made, stated to be false in some strains, and the direction of the resulting error is given: the tabulated numbers are minima.
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what this limits: the counts of kinds of chromosomes in table 2: they rest on an assumption the authors state is violated in some strains, so the numbers are minima rather than estimates
limitations[3]1.0the tagger's words
limitationsThe baseline the experiment is compared against is inferred rather than observed, and the authors offer that as one of two explanations for the unexpected control differences.
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what this limits: the control samples as showing the initial composition: the authors note the initial population's composition is inferred from its parents, and offer sampling error as the alternative explanation
limitations[4]1.0the tagger's words
controlsa Control sample whose gene-arrangement frequencies should match the initial population, against which the experimental cages are read
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eliminates: drift and sampling as the explanation of a frequency change - the Control sample is the one that should show no change, and it is what makes a change elsewhere readable · outcome (stated by the tagger, no quotation): held
controls[0]0.85the tagger's words
conceptsgene arrangement
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concepts[0]the paper's words
conceptsStandard
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also in: Standard
concepts[1]the paper's words
conceptspopulation cage
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concepts[2]the paper's words
sensesevidence of selection - a TWO-PART criterion: the average rate of change per generation AND the regression of that rate on chromosome frequency, both of which must be considered
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senses[0]1.0the tagger's words
sensesevidence of selection - AS A REGRESSION OF RATE ON FREQUENCY, which the paper says indicates selection EVEN IF the average does not differ significantly from zero
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about this quote: THE QUOTE CONTINUES A SENTENCE THAT THIS COPY CUTS IN TWO - a running head and a stray full stop stand between it and the words it follows, which read 'obviously indicates a selective' and, after the head, 'process,'.
senses[1]1.0the tagger's words
sensesinitial population composition - not measured but INFERRED from the composition of the parents, while the control sample describes something else
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senses[2]1.0the tagger's words
claim_relationsbuilds-on → L'Heritier and Teissier's population cage
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claim_relations[0]the tagger's words
claim_relationscontradicts → Hovanitz (1944) migration explanation of the seasonal changes at Pinon Flats and Andreas Canyon
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claim_relations[1]the tagger's words
concept_edgesStandard —is-a→ gene arrangement
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strength of the relation: 1
concept_edges[0]the tagger's words
content_tagschi-squared
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also in: chi-squared
content_tags.statistics[0]the tagger's words
content_tagst-test (Student's)
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content_tags.statistics[1]the tagger's words
content_tagsregression
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also in: regression
content_tags.statistics[2]the tagger's words
content_tagsF-test
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also in: F-test
content_tags.statistics[3]the tagger's words
content_tagsleast squares
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also in: least squares
content_tags.statistics[4]the tagger's words
content_tagsp-value
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also in: p-value
content_tags.statistics[5]the tagger's words
content_tagsvariance
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also in: variance
content_tags.statistics[6]the tagger's words
content_tagsIn population cages held at 25°C the frequency of the Standard gene arrangement rose highly significantly at the expense of the other arrangements, especially Chiricahua, whereas at 16.5°C mean frequencies did not change significantly.
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content_tags.findings[0]the tagger's words
content_tagsThe rate of frequency change per generation regressed negatively on frequency, meaning each chromosome type gained when it was rare and lost when it became common.
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content_tags.findings[1]the tagger's words
content_tagsFor cages containing only Standard and Chiricahua at 25°C, relative selective values of 0.70 for ST/ST, 1.00 for ST/CH and 0.30 for CH/CH reproduce the observed changes and put equilibrium at 70 percent Standard.
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content_tags.findings[2]the tagger's words
content_tagsWith all three chromosome types present, least-squares selective values (0.43 ST/ST, 0.05 AR/AR, 0.21 CH/CH, 1.30 ST/AR, 1.00 ST/CH, 0.71 AR/CH) place equilibrium at 53 percent Standard, 34 percent Arrowhead and 13 percent Chiricahua, and the assumption that the three heterozygotes are equally fit yields impossible values.
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content_tags.findings[3]the tagger's words
content_tagsThe data cannot discriminate equal selection in the two sexes from very unequal selection: values of 1.00:1.00:0.60 in females with 0.40:1.00:0 in males fit the observations as well as the sex-averaged values.
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content_tags.findings[4]the tagger's words
content_tagsBecause the cages at 25°C and 16.5°C were stocked with sibs, the presence of change at the high temperature and its absence at the low temperature can be attributed to temperature alone.
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content_tags.findings[5]the tagger's words
content_tagsVarying the food regime (two jars every three days versus one jar every five days) produced no consistent difference in the direction or size of the frequency changes.
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content_tags.findings[6]the tagger's words
content_tagsIn the 14th experiment Standard rose from 31 to 55 percent while Arrowhead fell from 69 to 45 percent.
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content_tags.findings[7]the tagger's words
content_tagsThe spring reversal seen in nature, in which Standard falls and Chiricahua rises, could not be reproduced in any population cage.
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content_tags.findings[8]the tagger's words
content_tagsMeasured fly dispersal rates are far too slow for migration from Keen Camp to explain the seasonal shift at Andreas Canyon 16 kilometres away.
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content_tags.findings[9]the tagger's words
content_tagsselective disadvantage
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content_tags.definitions[0]the tagger's words
content_tagsten-day period
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content_tags.definitions[1]the tagger's words
content_tagstemperature factor
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content_tags.variables[0]the tagger's words
content_tagsfood regime
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also in: food regime
content_tags.variables[1]the tagger's words
content_tagsgene arrangement
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content_tags.variables[2]the tagger's words
content_tagsfrequencies of chromosomes
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content_tags.variables[3]the tagger's words
content_tagsgene content
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also in: gene content
content_tags.variables[4]the tagger's words
content_tagss=.3o, t=.7o, q=.7o — Fitted selective disadvantage of ST/ST (0.30) and of CH/CH (0.70) relative to the heterozygote, and the resulting equilibrium frequency of Standard (0.70)
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content_tags.quantities[0]the tagger's words
content_tags53 percent Standard, 34 percent Arrowhead and 13 percent Chiricahua — Equilibrium frequencies computed for the three-chromosome experiments at 25°C
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content_tags.quantities[1]the tagger's words
content_tags124 ... 157 ... II3 ... average of 131 — Estimates of the effective number of breeding parents in a cage derived from the excess variance of frequency change, from Standard, Arrowhead and Chiricahua data respectively
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content_tags.quantities[2]the tagger's words
content_tags300 chromosomes — Number of third chromosomes scored per monthly sample from each cage, split into six subsamples
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content_tags.quantities[3]the tagger's words
content_tags3·5 weeks ... 5.2 weeks — Assumed generation interval used to convert observed frequency changes into rates per generation, at 25° and at 16.5° respectively
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content_tags.quantities[4]the tagger's words
content_tags3ooo-sooo flies per cage — Steady-state size of the experimental cage population at room temperature with one fresh food jar every other day
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content_tags.quantities[5]the tagger's words
content_tags71 percent to 42 percent — Fall in Chiricahua frequency in the 13th experiment, while Standard doubled
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content_tags.quantities[6]the tagger's words

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