---
OA_place: publisher
OA_type: hybrid
_id: '20655'
abstract:
- lang: eng
text: Traits that affect organismal fitness are often highly genetically variable.
This genetic variation is vital for populations to adapt to their environments,
but it is also surprising given that nature – after all – ‘selects’ the best genotypes
at the expense of those that fall short. Explaining the extensive genetic variation
of fitness‐related traits is thus a longstanding puzzle in evolutionary biology,
with cascading implications for ecology, conservation, and human health. Balancing
selection – an umbrella term for scenarios in which natural selection maintains
genetic variation – is a century‐old explanation to resolve this puzzle that has
gained recent momentum from genome‐scale methods for detecting it. Yet evaluating
whether balancing selection can, in fact, resolve the puzzle is challenging, given
the logistical constraints of distinguishing balancing selection from alternative
hypotheses and the daunting collection of theoretical models that formally underpin
this debate. Here, we track the development of balancing selection theory over
the last century and provide an accessible review of this rich collection of models.
We first outline the range of biological scenarios that can generate balancing
selection. We then examine how fundamental features of genetic systems – non‐random
mating between individuals, ploidy levels, genetic drift, linkage, and genetic
architectures of traits – have been progressively incorporated into the theory.
We end by linking these theoretical predictions to ongoing empirical efforts to
understand the evolutionary processes that explain genetic variation.
acknowledgement: 'We thank Brian Charlesworth, Deborah Charlesworth, and Sally Otto
for extensive comments and suggestions. We also thank Göran Arnqvist, Adam Eyre-Walker,
Philip Hedrick, Jitka Polechová, and Henrique Teotónio for further helpful comments
on the manuscript. This work was supported by a H2020 Marie Skłodowska-Curie COFUND
Action fellowship (#101034413, to F. R.), the Birgitta Sintring Foundation (#S2024-0007,
to M. K. Z.), the Research Council of Norway (302619, to D. G.), the Alexander von
Humboldt Foundation (to H. K.), the Swiss National Science Foundation (#211549,
to X. L. R.), the Swedish Research Council (#2022-03603, to CO; #2020-03123, to
E. I. S.) and the European Research Council (ERC-2023-STG-#101117517, to C. O.).
We are particularly grateful to the European Society for Evolutionary Biology for
funding a Special Topics Network workshop (to T. C., H. K., E. I. S.), from which
this review began. Open Access funding provided by Institute of Science and Technology
Austria/KEMÖ.'
article_number: 804-825
article_processing_charge: Yes (via OA deal)
article_type: original
author:
- first_name: Filip
full_name: Ruzicka, Filip
id: 347955dd-57b0-11ee-9095-c28bdd368f4b
last_name: Ruzicka
- first_name: Martyna K.
full_name: Zwoinska, Martyna K.
last_name: Zwoinska
- first_name: Debora
full_name: Goedert, Debora
last_name: Goedert
- first_name: Hanna
full_name: Kokko, Hanna
last_name: Kokko
- first_name: Xiang‐Yi
full_name: Li Richter, Xiang‐Yi
last_name: Li Richter
- first_name: Iain R.
full_name: Moodie, Iain R.
last_name: Moodie
- first_name: Sofie
full_name: Nilén, Sofie
last_name: Nilén
- first_name: Colin
full_name: Olito, Colin
last_name: Olito
- first_name: Erik I.
full_name: Svensson, Erik I.
last_name: Svensson
- first_name: Peter
full_name: Czuppon, Peter
last_name: Czuppon
- first_name: Tim
full_name: Connallon, Tim
last_name: Connallon
citation:
ama: Ruzicka F, Zwoinska MK, Goedert D, et al. A century of theories of balancing
selection. Biological Reviews. 2026;101(2). doi:10.1111/brv.70103
apa: Ruzicka, F., Zwoinska, M. K., Goedert, D., Kokko, H., Li Richter, X., Moodie,
I. R., … Connallon, T. (2026). A century of theories of balancing selection. Biological
Reviews. Wiley. https://doi.org/10.1111/brv.70103
chicago: Ruzicka, Filip, Martyna K. Zwoinska, Debora Goedert, Hanna Kokko, Xiang‐Yi
Li Richter, Iain R. Moodie, Sofie Nilén, et al. “A Century of Theories of Balancing
Selection.” Biological Reviews. Wiley, 2026. https://doi.org/10.1111/brv.70103.
ieee: F. Ruzicka et al., “A century of theories of balancing selection,”
Biological Reviews, vol. 101, no. 2. Wiley, 2026.
ista: Ruzicka F, Zwoinska MK, Goedert D, Kokko H, Li Richter X, Moodie IR, Nilén
S, Olito C, Svensson EI, Czuppon P, Connallon T. 2026. A century of theories of
balancing selection. Biological Reviews. 101(2), 804–825.
mla: Ruzicka, Filip, et al. “A Century of Theories of Balancing Selection.” Biological
Reviews, vol. 101, no. 2, 804–825, Wiley, 2026, doi:10.1111/brv.70103.
short: F. Ruzicka, M.K. Zwoinska, D. Goedert, H. Kokko, X. Li Richter, I.R. Moodie,
S. Nilén, C. Olito, E.I. Svensson, P. Czuppon, T. Connallon, Biological Reviews
101 (2026).
corr_author: '1'
das_tickbox: '0'
date_created: 2025-11-19T09:43:50Z
date_published: 2026-04-01T00:00:00Z
date_updated: 2026-07-27T08:08:09Z
day: '01'
ddc:
- '570'
department:
- _id: BeVi
doi: 10.1111/brv.70103
ec_funded: 1
external_id:
isi:
- '001614285900001'
pmid:
- '41235821 '
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keyword:
- evolutionary theory
- population genetics
- balancing selection
- heterozygote advantage
- trade-offs
- negative frequency-dependent selection
- fitness variation
- mathematical modelling
language:
- iso: eng
license: https://creativecommons.org/licenses/by-nc/4.0/
month: '04'
oa: 1
oa_version: Published Version
pmid: 1
project:
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call_identifier: H2020
grant_number: '101034413'
name: 'IST-BRIDGE: International postdoctoral program'
publication: Biological Reviews
publication_identifier:
eissn:
- 1469-185X
issn:
- 1464-7931
publication_status: published
publisher: Wiley
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supplementarymaterial: yes
title: A century of theories of balancing selection
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...
---
_id: '5553'
abstract:
- lang: eng
text: "Genotypic, phenotypic and demographic data for 2128 wild snapdragons and
1127 open-pollinated progeny from a natural hybrid zone, collected as part of
Tom Ellis' PhD thesis (submitted) February 2016).\r\n\r\nTissue samples were sent
to LGC Genomics in Berlin for DNA extraction, and genotyping at 70 SNP markers
by KASPR genotyping. 29 of these SNPs failed to amplify reliably, and have been
removed from this dataset.\r\n\r\nOther data were retreived from an online database
of this population at www.antspec.org."
article_processing_charge: No
author:
- first_name: David
full_name: Field, David
id: 419049E2-F248-11E8-B48F-1D18A9856A87
last_name: Field
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- first_name: Thomas
full_name: Ellis, Thomas
id: 3153D6D4-F248-11E8-B48F-1D18A9856A87
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orcid: 0000-0002-8511-0254
citation:
ama: Field D, Ellis T. Inference of mating patterns among wild snapdragons in a
natural hybrid zone in 2012. 2016. doi:10.15479/AT:ISTA:37
apa: Field, D., & Ellis, T. (2016). Inference of mating patterns among wild
snapdragons in a natural hybrid zone in 2012. Institute of Science and Technology
Austria. https://doi.org/10.15479/AT:ISTA:37
chicago: Field, David, and Thomas Ellis. “Inference of Mating Patterns among Wild
Snapdragons in a Natural Hybrid Zone in 2012.” Institute of Science and Technology
Austria, 2016. https://doi.org/10.15479/AT:ISTA:37.
ieee: D. Field and T. Ellis, “Inference of mating patterns among wild snapdragons
in a natural hybrid zone in 2012.” Institute of Science and Technology Austria,
2016.
ista: Field D, Ellis T. 2016. Inference of mating patterns among wild snapdragons
in a natural hybrid zone in 2012, Institute of Science and Technology Austria,
10.15479/AT:ISTA:37.
mla: Field, David, and Thomas Ellis. Inference of Mating Patterns among Wild
Snapdragons in a Natural Hybrid Zone in 2012. Institute of Science and Technology
Austria, 2016, doi:10.15479/AT:ISTA:37.
short: D. Field, T. Ellis, (2016).
contributor:
- contributor_type: project_manager
first_name: Nicholas H
id: 4880FE40-F248-11E8-B48F-1D18A9856A87
last_name: Barton
orcid: 0000-0002-8548-5240
datarep_id: '37'
date_created: 2018-12-12T12:31:30Z
date_published: 2016-02-19T00:00:00Z
date_updated: 2026-04-09T10:52:06Z
day: '19'
ddc:
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doi: 10.15479/AT:ISTA:37
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file_size: 132808
relation: main_file
file_date_updated: 2020-07-14T12:47:01Z
has_accepted_license: '1'
keyword:
- paternity assignment
- pedigree
- matting patterns
- assortative mating
- Antirrhinum majus
- frequency-dependent selection
- plant-pollinator interaction
license: https://creativecommons.org/publicdomain/zero/1.0/
month: '02'
oa: 1
oa_version: Published Version
publisher: Institute of Science and Technology Austria
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title: Inference of mating patterns among wild snapdragons in a natural hybrid zone
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...