Editing Handicap principle (section)

== History ==

=== Origins ===

The handicap principle was proposed in 1975 by the [[Israel|Israeli]] biologist [[Amotz Zahavi]]. He argued that mate choice involving what he called "signal selection" would lead to [[honest signalling|"honest" or reliable signalling]] between male and female animals, even though they have an interest in bluffing or deceiving each other. The handicap principle asserts that secondary sexual characteristics are costly signals, which are reliable indicators of the signaller's quality, since they cost the signaller resources that lower-quality individuals could not afford.<ref name="Zahavi 1975 pp. 205–214"/><ref name="Zahavi 1977 pp. 603–605"/><ref name="Zahavi 1997">{{cite book |last=Zahavi |first=Amotz |title=The handicap principle: a missing piece of Darwin's puzzle |publisher=Oxford University Press |location=New York |year=1997 |isbn=978-0-19-510035-8 |oclc=35360821 |url-access=registration |url=https://archive.org/details/handicapprincipl0000zeha}}</ref> The generality of the phenomenon is a matter of some debate and disagreement, and Zahavi's views on the scope and importance of handicaps in biology have not been accepted by the mainstream.<ref>{{cite journal |last1=Grose |first1=Jonathan |title=Modelling and the fall and rise of the handicap principle |journal=Biology & Philosophy |date=7 June 2011 |volume=26 |issue=5 |pages=677–696 |doi=10.1007/s10539-011-9275-1 |s2cid=84600072 }}</ref><ref>Review by {{cite journal |first1=Andrew |last1=Pomiankowski |last2=Iwasa |first2=Y. |year=1998 |title=Handicap Signaling: Loud and True? |journal=[[Evolution (journal)|Evolution]] |volume=52 |issue=3 |pages=928–932 |doi=10.2307/2411290 |jstor=2411290 |s2cid=53060420 |url=https://semanticscholar.org/paper/9fd8edb7b18bd5e6666e798e5c7679b2b4b0993b }}</ref> Nevertheless, the idea has been very influential, with most researchers in the field believing that the theory explains some aspects of animal communication.<ref name="Johnstone97">{{cite journal |last=Johnstone |first=R. A. |year=1995 |title=Sexual selection, honest advertisement and the handicap principle: reviewing the evidence |journal=[[Biological Reviews]] |volume=70 |issue=1 |pages=1–65 |doi=10.1111/j.1469-185X.1995.tb01439.x |pmid=7718697 |s2cid=40322800 }}</ref><ref>{{cite book |last=Johnstone |first=Rufus A. |year=1997 |chapter=The Evolution of Animal Signals |title=Behavioural Ecology: An Evolutionary Approach |url=https://archive.org/details/behaviouralecolo00kreb |url-access=limited |edition=4th |editor-first=J. R. |editor-last=Krebs |editor2-first=N. B. |editor2-last=Davies |publisher=Blackwell |pages=[https://archive.org/details/behaviouralecolo00kreb/page/n164 155]–178 |isbn=978-0865427310 }}</ref><ref>{{cite book |last1=Maynard Smith |first1=John |author1-link=John Maynard Smith |last2=Harper |first2=David |author2-link=David Harper (biologist) |year=2003 |chapter=The theory of costly signalling |title=Animal Signals |publisher=[[Oxford University Press]] |pages=16–31 |isbn=978-0-19-852685-8}}</ref>

=== Grafen's signaling game model ===

{{further|Signaling game}}

[[File:Handicap-signal-of-quality.png|thumb|upright=1.5|Graph based on Johnstone's 1997 graphical representation of a Zahavian handicap. Where <math>C_L</math> is cost to a low-quality signaller and <math>C_H</math> is cost to a high-quality signaller. Optimal signalling levels are <math>S^*_L</math> for a low-quality signaller, and <math>S^*_H</math> for a high-quality signaller.<ref name="Johnstone97"/>|alt=Graph showing mathematically how a handicap would in theory work]]

The handicap principle was initially controversial,<ref name="Davis 1976">{{cite journal |last1=Davis |first1=J. W. F. |last2=O'Donald |first2=P. |year=1976 |title=Sexual selection for a handicap: A critical analysis of Zahavi's model |journal=Journal of Theoretical Biology |volume=57 |issue=2 |pages=345–354 |doi=10.1016/0022-5193(76)90006-0 |pmid=957664 |bibcode=1976JThBi..57..345D }}</ref><ref name="Eshel 1978">{{cite journal |last=Eshel |first=I. |year=1978 |title=On the Handicap Principle—A Critical Defence |journal=Journal of Theoretical Biology |volume=70 |issue=2 |pages=245–250 |doi=10.1016/0022-5193(78)90350-8 |pmid=633919 |bibcode=1978JThBi..70..245E }}</ref><ref name="Kirkpatrick 1986">{{cite journal |last=Kirkpatrick |first=M. |year=1986 |title=The handicap mechanism of sexual selection does not work |journal=[[American Naturalist]] |volume=127 |issue=2 |pages=222–240 |doi=10.1086/284480|jstor=2461351 |s2cid=83984463 }}</ref><ref name="Pomiankowski 1987">{{cite journal |last=Pomiankowski |first=A. |year=1987 |title=Sexual selection: The handicap principle does work sometimes |journal=[[Proceedings of the Royal Society B]] |volume=231 |issue=1262 |pages=123–145 |doi=10.1098/rspb.1987.0038 |bibcode=1987RSPSB.231..123P |s2cid=144837163 }}</ref> with the British biologist [[John Maynard Smith]] a notable early critic of Zahavi's ideas.<ref name="Maynard Smith 1976">{{cite journal |last=Maynard Smith |first=John |author-link=John Maynard Smith |year=1976 |title=Sexual selection and the handicap principle |journal=Journal of Theoretical Biology |volume=57 |issue=1 |pages=239–242 |doi=10.1016/S0022-5193(76)80016-1 |pmid=957656 |bibcode=1976JThBi..57..239S }}</ref><ref>{{cite journal |last=Maynard Smith |first=John |author-link=John Maynard Smith |year=1978 |title=The Handicap Principle—A Comment |journal=Journal of Theoretical Biology |volume=70 |issue=2 |pages=251–252 |doi=10.1016/0022-5193(78)90351-X |pmid=633920 |bibcode=1978JThBi..70..251S }}</ref><ref>{{cite journal |last=Maynard Smith |first=John |author-link=John Maynard Smith |year=1985 |title=Mini Review: Sexual Selection, Handicaps and True Fitness |journal=Journal of Theoretical Biology |volume=115 |issue=1 |pages=1–8 |doi=10.1016/S0022-5193(85)80003-5 |pmid=4033159 }}</ref> However, the handicap principle gained wider acceptance because it is supported by [[game theory]] models, most notably the Scottish biologist [[Alan Grafen]]'s 1990 [[signalling game]] model.<ref name="Grafen 1990">{{cite journal |last=Grafen |first=A. |year=1990 |title=Biological signals as handicaps |journal=Journal of Theoretical Biology |volume=144 |issue=4 |pages=517–546 |doi=10.1016/S0022-5193(05)80088-8 |pmid=2402153|bibcode=1990JThBi.144..517G }}</ref> This was essentially a rediscovery of the Canadian-American economist [[Michael Spence]]'s [[Signaling (economics)|job market signalling model]],<ref>{{cite journal |last=Spence |first=A. M. |year=1973 |title=Job Market Signaling |journal=[[Quarterly Journal of Economics]] |volume=87 |issue=3 |pages=355–374 |doi=10.2307/1882010 |jstor=1882010 }}</ref> where the job applicant signals their quality by declaring a costly education. In Grafen's model, the courting male's quality is signalled by investment in an extravagant trait—similar to the [[peacock]]'s tail. The signal is reliable if the cost to the signaller of producing it is proportionately lower for higher-quality signallers than for lower-quality ones.<ref name="Grafen 1990"/>

A series of papers by the American biologist Thomas Getty showed that Grafen's proof of the handicap principle depends on the critical, simplifying assumption that signallers trade off costs for benefits in an additive fashion, analogous to the way humans invest money to increase income in the same currency.<ref>{{cite journal |last=Getty |first=T. |year=1998a |title=Handicap signalling: when fecundity and viability do not add up |journal=[[Animal Behaviour (journal)|Animal Behaviour]] |volume=56 |issue=1 |pages=127–130 |doi=10.1006/anbe.1998.0744 |pmid=9710469|s2cid=36731320 }}</ref><ref>{{cite journal |last=Getty |first=T. |year=1998b |title=Reliable signalling need not be a handicap |journal=Anim. Behav. |volume=56 |issue=1 |pages=253–255 |doi=10.1006/anbe.1998.0748 |pmid=9710484 |s2cid=34066689 }}</ref><ref>{{cite journal |last=Getty |first=Thomas |year=2002 |title=Signaling health versus parasites |journal=[[American Naturalist]] |volume=159 |issue=4 |pages=363–371 |doi=10.1086/338992 |jstor=338992 |pmid=18707421 |s2cid=12598696 }}</ref><ref name="Getty 2006">{{cite journal |last=Getty |first=T. |year=2006 |title=Sexually selected signals are not similar to sports handicaps |journal=[[Trends in Ecology & Evolution]] |volume=21 |issue=2 |pages=83–88 |doi=10.1016/j.tree.2005.10.016 |pmid=16701479 }}</ref> This is illustrated in the figures from Johnstone 1997, which show that the optimum signalling levels are different for low- and high-quality signallers.<ref name="Johnstone97"/> The validity of the assumption that costs and benefits are additive has been contested, in its application to the evolution of [[signalling theory|sexually selected signals]]. It can be reasoned that since fitness depends on the production of offspring, this is a multiplicative rather than additive function of reproductive success.<ref>{{cite journal |last1=Nur |first1=N. |last2=Hasson |first2=O. |year=1984 |title=Phenotypic plasticity and the handicap principle |journal=J. Theor. Biol. |volume=110 |issue=2 |pages=275–297 |doi=10.1016/S0022-5193(84)80059-4 |bibcode=1984JThBi.110..275N }}</ref>

Further game theoretical models demonstrated the [[Evolutionarily stable strategy|evolutionary stability]] of handicapped signals in nestlings' begging calls,<ref name="Godfray 1991">{{cite journal |last=Godfray |first=H. C. J. |year=1991 |title=Signalling of need by offspring to their parents |journal=[[Nature (journal)|Nature]] |volume=352 |issue=6333 |pages=328–330 |doi=10.1038/352328a0 |bibcode=1991Natur.352..328G |s2cid=4288527 }}</ref> in predator-deterrent signals<ref>{{cite journal |last=Yachi |first=S. |year=1995 |title=How can honest signalling evolve? The role of the handicap principle |journal=[[Proceedings of the Royal Society B]] |volume=262 |issue=1365 |pages=283–288 |doi=10.1098/rspb.1995.0207 |s2cid=85339637 }}</ref> and in threat-displays.<ref>{{cite journal |last1=Adams |first1=E. S. |last2=Mesterton-Gibbons |first2=M. |year=1995 |title=The cost of threat displays and the stability of deceptive communication |journal=Journal of Theoretical Biology |volume=175 |issue=4 |pages=405–421 |doi=10.1006/jtbi.1995.0151 |bibcode=1995JThBi.175..405A |doi-access=free }}</ref><ref>{{cite journal |last=Kim |first=Y-G. |year=1995 |title=Status signalling games in animal contests |journal=Journal of Theoretical Biology |volume=176 |issue=2 |pages=221–231 |doi=10.1006/jtbi.1995.0193 |pmid=7475112 |bibcode=1995JThBi.176..221K }}</ref> In the classic handicap models of begging in game theory, all players are assumed to pay the same amount to produce a signal of a given level of intensity, but differ in the relative value of eliciting the desired response (donation) from the receiver. The hungrier the baby bird, the more food is of value to it, and the higher the optimal signalling level (the louder its chirping).<ref name="Godfray 1991"/>

=== Cheap talk models without handicaps ===

{{further|Cheap talk}}

Counter-examples to handicap models predate handicap models themselves. Models of signals (such as [[Deimatic behaviour|threat displays]]) without any handicapping costs show that what biologists call [[cheap talk]] may be an evolutionarily stable form of communication.<ref>{{cite journal |last=Enquist |first=M. |year=1985 |title=Communication during aggressive interactions with particular reference to variation in choice of behaviour |journal=Animal Behaviour |volume=33 |issue=4 |pages=1152–1161 |doi=10.1016/S0003-3472(85)80175-5 |s2cid=53200843 }}</ref> Analysis of some begging models shows that non-communication strategies are not only evolutionarily stable, but lead to higher payoffs for both players.<ref>{{cite journal |last1=Rodriguez-Girones |first1=M. A. |last2=Cotton |first2=P. A. |last3=Kacelnik |first3=A. |year=1996 |title=The evolution of begging: signaling and sibling competition |journal=[[Proceedings of the National Academy of Sciences of the United States of America]] |volume=93 |issue=25 |pages=14637–14641 |doi=10.1073/pnas.93.25.14637|pmid=8962106 |pmc=26187 |bibcode=1996PNAS...9314637R |doi-access=free }}</ref><ref>{{cite journal |last1=Lachmann |first1=M. |author-link2=Carl Bergstrom |last2=Bergstrom |first2=C. T. |year=1998 |title=Signalling among relatives. II. Beyond the tower of babel |journal=Theoretical Population Biology |volume=54 |issue=2 |pages=146–160 |doi=10.1006/tpbi.1997.1372 |pmid=9733656|doi-access=free |bibcode=1998TPBio..54..146L }}</ref> In human [[mate choice]], mathematical analyses including [[Monte Carlo method|Monte Carlo simulations]] suggest that costly traits ought to be more attractive to the other sex and much rarer than non-costly traits.<ref>{{cite journal |last=Kock |first=N. |year=2011 |url=http://cits.tamiu.edu/kock/Pubs/journals/2011JournalJEP/Kock_2011_JEP_EvoMateChTrts.pdf |title=A mathematical analysis of the evolution of human mate choice traits: Implications for evolutionary psychologists |journal=Journal of Evolutionary Psychology |volume=9 |issue=3 |pages=219–247 |doi=10.1556/jep.9.2011.3.1}}</ref>

It was soon discovered that honest signals need not be costly at the honest equilibrium, even under conflict of interest. This conclusion was first shown in [[Discrete modelling|discrete models]]<ref>{{Cite journal |last=Hurd |first=Peter L. |date=May 1995 |title=Communication in discrete action-response games |url=http://dx.doi.org/10.1006/jtbi.1995.0093 |journal=Journal of Theoretical Biology |volume=174 |issue=2 |pages=217–222 |doi=10.1006/jtbi.1995.0093 |bibcode=1995JThBi.174..217H |issn=0022-5193|url-access=subscription }}</ref><ref>{{Cite journal |last=Számadó |first=Szabolcs |date=June 1999 |title=The Validity of the Handicap Principle in Discrete Action–Response Games |url=http://dx.doi.org/10.1006/jtbi.1999.0935 |journal=Journal of Theoretical Biology |volume=198 |issue=4 |pages=593–602 |doi=10.1006/jtbi.1999.0935 |pmid=10373357 |bibcode=1999JThBi.198..593S |issn=0022-5193|url-access=subscription }}</ref> and then in [[Continuous modelling|continuous models]].<ref>{{Cite journal |last1=Lachmann |first1=Michael |last2=Számadó |first2=Szabolcs |last3=Bergstrom |first3=Carl T. |date=2001-10-30 |title=Cost and conflict in animal signals and human language |journal=Proceedings of the National Academy of Sciences |volume=98 |issue=23 |pages=13189–13194 |doi=10.1073/pnas.231216498 |pmid=11687618 |issn=0027-8424|pmc=60846 |doi-access=free |bibcode=2001PNAS...9813189L }}</ref><ref>{{Cite journal |last1=Számadó |first1=Szabolcs |last2=Czégel |first2=Dániel |last3=Zachar |first3=István |date=2017-12-28 |title=One problem, too many solutions: How costly is honest signalling of need? |journal=PLOS ONE |volume=14 |issue=1 |pages=e0208443 |doi=10.1371/journal.pone.0208443|doi-access=free |biorxiv=10.1101/240440 |pmid=30633748 |pmc=6329501 }}</ref><ref>{{Cite journal |last1=Számadó |first1=Szabolcs |last2=Zachar |first2=István |last3=Czégel |first3=Dániel |last4=Penn |first4=Dustin J. |date=2023-01-08 |title=Honesty in signalling games is maintained by trade-offs rather than costs |journal=BMC Biology |volume=21 |issue=1 |page=4 |doi=10.1186/s12915-022-01496-9 |pmid=36617556 |issn=1741-7007|pmc=9827650 |doi-access=free }}</ref> Similar results were obtained in [[Conflict theories|conflict models]]: threat displays need not be handicaps to be honest and evolutionarily stable.<ref name="Számadó 2003 pp. 327–348">{{cite journal |last=Számadó |first=Szabolcs |title=Threat Displays are not Handicaps |journal=Journal of Theoretical Biology |publisher=Elsevier |volume=221 |issue=3 |year=2003 |issn=0022-5193 |doi=10.1006/jtbi.2003.3176 |pages=327–348|pmid=12642112 |bibcode=2003JThBi.221..327S }}</ref>

=== Unworkable theory lacking empirical evidence ===

In 2015, Simon Huttegger and colleagues wrote that the distinction between "indexes" (unfakable signals) and "fakable signals", crucial to the argument for the handicap principle, is an artefact of signalling models. They demonstrated that absent that dichotomy, cost could not be the only factor controlling signalling behaviours, and that indeed it was "probably not the most important" factor acting against deception.<ref name="Huttegger Bruner Zollman 2015">{{cite journal |last1=Huttegger |first1=Simon M. |last2=Bruner |first2=Justin P. |last3=Zollman |first3=Kevin J. S. |title=The Handicap Principle Is an Artifact |journal=Philosophy of Science |volume=82 |issue=5 |date=2015 |issn=0031-8248 |doi=10.1086/683435 |pages=997–1009 |jstor=10.1086/683435 |url=https://figshare.com/articles/journal_contribution/6492797 }}</ref>

Dustin J. Penn and Szabolcs Számadó stated in 2019 that there was still no [[empirical evidence]] for evolutionary pressure for wasteful biology or acts, and proposed that the handicap principle should be abandoned.<ref name="Penn Számadó 2019 pp. 267–290">{{cite journal |last1=Penn |first1=Dustin J. |last2=Számadó |first2=Szabolcs |title=The Handicap Principle: how an erroneous hypothesis became a scientific principle |journal=Biological Reviews |publisher=Wiley |volume=95 |issue=1 |date=23 October 2019 |issn=1464-7931 |doi=10.1111/brv.12563 |pages=267–290|doi-access=free |pmid=31642592 |pmc=7004190 }}</ref>