Szabolcs Számadó is a theoretical biologist. His main research interest is honest signalling, which he investigates with a range of tools including game theory, lab experiments and individual based modelling. His research includes a broad range of topics from the evolution of cooperation to the evolution of early human language. His latest interest is the role of reputation systems in the maintenance of cooperation and role of communication in the role maintenance of reputation. He published in top journals of the field (Proceedings of the National Academy of Sciences, Biological Reviews, Philosophical Transactions of the Royal Society B). He is the leading editor of a special issue on reputation systems ‘The language of cooperation: reputation and honest signalling’ published in the Philosophical Transactions of the Royal Society B.
Last updated: 2024.09.28
The trade-offs of honest and dishonest signals (PREPRINT)
Szabolcs Számadó , István Zachar, Dustin J. Penn
Explaining the evolution of honest versus dishonest signals under conflicts of interest has long posed a major challenge, but several recent developments should spur renewed interest in this problem. First, the Handicap Principle, which maintains that signals must be costly to be honest, has been refuted and the model that claimed to validate this idea has been shown to have been misinterpreted. Second, more recent theoretical models demonstrate that signal honesty can be maintained by condition-dependent signalling trade-offs rather than costs. Third, we propose that signalling trade-offs may provide a general theory of honest signalling. According to signalling trade-off theory, signallers that differ in quality face different trade-offs at the honest equilibrium and therefore they are bound to invest differently. Such differential trade-offs, or lack of, can explain honest versus dishonest signals according to both experiments and models. Signalling trade-offs are found in every example of honest communication in nature under conflict of interest. Moreover, signalling trade-offs couple various fitness components, including both short-term investments into long-term fitness benefits, providing the necessary link between proximate and evolutionary explanations. Furthermore, trade-offs can also help bridge biological and economic theories of honest communication, which have developed independently in parallel for decades.
Számadó, S., Zachar, I., & Penn, D. J. (2023). The trade-offs of honest and dishonest signals.
Tautology explains evolution without variation and selection. A Comment on: ‘An evolutionary process without variation and selection’ (2021), by Gabora et al.
István Zachar, Máté Jakab and Szabolcs Számadó
Gabora and Steel (Gabora L, Steel M. 2021 An evolutionary process without variation and selection. J. R. Soc. Interface 18, 20210334. [doi:10.1098/rsif.2021.0334]) claim that cumulative adaptive evolution is possible without natural selection, that is, without variation and competition. To support this claim, the authors modelled a theoretical process called self–other reorganization (SOR) that envisages a population of reflexively autocatalytic sets that can accumulate beneficial changes without any form of birth, death or selection, that is without population dynamics. The authors claim that despite being non-Darwinian, adaptive evolution happens in SOR, deeming it relevant to the origin of life and to cultural evolution. We analysed SOR and the claim that it implements evolution without variation and selection. We found that the authors, by design, ignore the growth and/or degradation of autocatalytic sets or their components, assuming all effects are beneficial and all entities in SOR are identical and immutable. We prove that due to these assumptions, SOR is a trivial model of horizontal percolation of beneficial effects over a static population. We implemented an extended model of SOR including more realistic assumptions to prove that accounting for any of the ignored processes inevitably leads to conventional Darwinian dynamics. Our analysis directly challenges the authors’ claims, revealing evidence of an overly fragile foundation. While the best-case scenario the authors incorrectly generalize from may be mathematically valid, stripping away their unrealistic assumptions reveals that SOR does not represent real entities (e.g. protocells) but rather models the triviality that fast horizontal diffusion of effects can effectively equalize a population. Adaptation in SOR is solely because the authors only consider beneficial effects. The omission of death/growth dynamics and maladaptive effects renders SOR unrealistic and its relevance to evolution, cultural or biological, questionable.
Zachar, I., Máté, J., & Számadó, S. (2024). Tautology explains evolution without variation and selection. A Comment on:‘An evolutionary process without variation and selection’(2021), by Gabora et al. Journal of the Royal Society Interface, 21(218), 20230579.
Cue-driven microbial cooperation and communication: evolving quorum sensing with honest signalling
Tamás Czárán, István Scheuring, István Zachar and Szabolcs Számadó
Conclusions: Comparing the results of the four different modelling approaches indicates that cue-driven threshold cooperation may be a viable evolutionary strategy for microbes that cannot keep track of past behavior of their potential cooperating partners, in spatially viscous and in well-mixed environments alike. Our model can be seen as a version of the famous greenbeard effect, where greenbeards coexist with defectors in a evolutionarily stable polymorphism. Such polymorphism is maintained by the condition-dependent trade-offs of signal production which are characteristic of cue-based QS.
Czárán, T., Scheuring, I., Zachar, I., & Számadó, S. (2024). Cue-driven microbial cooperation and communication: evolving quorum sensing with honest signaling. BMC biology, 22(1), 73.
Honesty in signalling games is maintained by trade-offs rather than costs.
Számadó, S., Zachar, I., Czégel, D., & Penn, D. J.
Conclusions
Our results refute the claim that signals must be costly at the evolutionary equilibrium to be reliable,
as predicted by the Handicap Principle and so-called ‘costly signalling’ theory. Thus, our results raise serious concerns
about the handicap paradigm. We argue that the evolution of reliable signalling is better understood within a Darwinian
life-history framework, and that the conditions for honest signalling are more clearly stated and understood by
evaluating their trade-offs rather than their costs per se. We discuss potential shortcomings of equilibrium models
and we provide testable predictions to help advance the field and establish a better explanation for honest signals.
Last but not least, our results highlight why signals are expected to be efficient rather than wasteful.
Számadó, S., Zachar, I., Czégel, D., & Penn, D. J. (2023). Honesty in signalling games is
maintained by trade-offs rather than costs. BMC Biology, 21(1), 1-16.
Condition-dependent trade-offs maintain honest signalling.
Számadó, S., Samu, F., & Takács, K.
How and why animals and humans signal reliably is a key issue
in biology and social sciences that needs to be understood
to explain the evolution of communication. In situations in
which the receiver needs to differentiate between low- and
high-quality signallers, once a ruling paradigm, the Handicap
Principle has claimed that honest signals have to be costly to
produce. Subsequent game theoretical models, however,
highlighted that honest signals are not necessarily costly.
Honesty is maintained by the potential cost of cheating: by the
difference in the marginal benefit to marginal cost for low
versus high-quality signallers; i.e. by differential trade-offs.
Owing to the difficulties of manipulating signal costs and
benefits, there is lack of empirical tests of these predictions. We
present the results of a laboratory decision-making experiment
with human participants to test the role of equilibrium signal
cost and signalling trade-offs for the development of honest
communication. We found that the trade-off manipulation had
a much higher influence on the reliability of communication
than the manipulation of the equilibrium cost of signal.
Contrary to the predictions of the Handicap Principle, negative
production cost promoted honesty at a very high level in the
differential trade-off condition.
Számadó, S., Samu, F., & Takács, K. (2022). Condition-dependent trade-offs maintain honest
signalling. Royal Society Open Science, 9(10), 220335.
The language of cooperation: reputation and honest signalling
A theme issue compiled and edited by Szabolcs Számadó, Daniel Balliet, Francesca Giardini, Eleanor A Power and Károly Takács
About this issue
Large-scale non-kin cooperation is a unique ingredient of human success. This type of cooperation is challenging to explain in a world of self-interested individuals. This theme issue promotes an interdisciplinary approach that allows us to explore and to understand the evolution and the maintenance of reputation systems, with emphasis on gossip and honest signalling. The articles in this special issue draw our attention to the complexities of the workings of reputation systems, asking: (i) What are the necessary conditions for reputation-based systems? (ii) What is the content and context of reputation systems? (iii) How can reputations promote cooperation? And (iv) What is the role of gossip in maintaining reputation systems and thus cooperation?
Honesty and dishonesty in gossip strategies: a fitness interdependence analysis
Wu, J., Számadó, S., Barclay, P., Beersma, B., Dores Cruz, T. D., Iacono, S. L., … & Van Lange, P. A.
We build formal models
to provide the theoretical foundation for individuals’ gossip strategies, taking
into account the gossiper’s fitness interdependence with the receiver and the
target. Our models across four different games suggest a very simple rule:
when there is a perfect match (mismatch) between fitness interdependence
andthe effect of honest gossip, the gossiper should always be honest (dishonest);
however, in the case of a partial match, the gossiper shouldmake a choice based
on their fitness interdependence with the receiver and the target and the marginal
cost/benefit in terms of pay-off differences caused by possible choices of
the receiver and the target in the game. Moreover, gossipers can use this
simple rule to make optimal decisions even under noise. We discuss empirical
examples that support the predictions of our model and potential extensions.
Wu, J., Számadó, S., Barclay, P., Beersma, B., Dores Cruz, T. D., Iacono, S. L., … & Van Lange,
P. A. (2021). Honesty and dishonesty in gossip strategies: a fitness interdependence analysis.
Philosophical Transactions of the Royal Society B, 376(1838), 20200300.
Cooperating to show that you care: costly helping as an honest signal of fitness interdependence.
Barclay, P., Bliege Bird, R., Roberts, G., & Számadó, S.
We present amathematical
model in which agents help others based on their stake in the recipient’s
welfare, and recipients use that information to assess whom to trust. At equilibrium,
helping is a costly signal of stake: helping is worthwhile for those
who value the recipient (and thus will repay any trust), but is not worthwhile
for those who do not value the recipient (and thus will betray the trust). Recipients
demand signals when they value the signallers less and when the cost
of betrayed trust is higher; signal costs are higher when signallers have more
incentive to defect. Signalling systems are more likely when the trust games
resemble Prisoner’s Dilemmas, Stag Hunts or Harmony Games, and are
less likely in Snowdrift Games. Furthermore, we find that honest signals
need not benefit recipients and can even occur between hostile parties. By signalling
their interdependence, organisms benefit from increased trust, even
when no future interactions will occur.
Barclay, P., Bliege Bird, R., Roberts, G., & Számadó, S. (2021). Cooperating to show that you
care: costly helping as an honest signal of fitness interdependence. Philosophical
Transactions of the Royal Society B, 376(1838), 20200292.
The Handicap Principle: how an erroneous hypothesis became a scientific principle.
Penn, DJ & Számadó, Sz
We show that Grafen’s models do not support the handicap
hypothesis, although they do support Zahavi’s second hypothesis, which proposes that males adjust their investment into
the expression of their sexual signals according to their condition and ability to bear the costs (and risks to their survival).
Rather than being wasteful over-investments, honest signals evolve in this scenario because selection favours efficient and
optimal investment into signal expression and minimizes signalling costs. This idea is very different from the handicap
hypothesis, but it has been widely misinterpreted and equated to the Handicap Principle. Theoretical studies have since
shown that signalling costs paid at the equilibrium are neither sufficient nor necessary to maintain signal honesty, and
that honesty can evolve through differential benefits, as well as differential costs. There have been increasing criticisms
of the Handicap Principle, but they have focused on the limitations of Grafen’s model and overlooked the fact that it is
not a handicap model. This model is better understood within a Darwinian framework of adaptive signalling trade-offs,
without the added burden and confusing logic of the Handicap Principle. There is no theoretical or empirical support
for the Handicap Principle and the time is long overdue to usher this idea into an ‘honorable retirement’.
Penn, DJ & Számadó, Sz (2020) The Handicap Principle: how an erroneous hypothesis
became a scientific principle. Biological Reviews 95 (1), 267-290.
Caring for parents: an evolutionary rationale.
Garay, J., Számadó, S., Varga, Z., & Szathmary, E.
Results: We show with a novel demographic model that the biological rule “During your reproductive period, give
some of your resources to your post-fertile parents” will spread even if the cost of support given to post-fertile
grandmothers considerably decreases the demographic parameters of fertile parents but radically increases the
survival rate of grandchildren. The teaching of vital cultural content is likely to have been critical in making
grandparental service valuable. We name this the Fifth Rule, after the Fifth Commandment that codifies such
behaviors in Christianity.
Conclusions: Selection for such behavior may have produced an innate moral tendency to honor parents even in
situations, such as those experienced today, when the quantitative conditions would not necessarily favor the
maintenance of this trait.
Garay, J., Számadó, S., Varga, Z., & Szathmary, E. (2018). Caring for parents: an evolutionary
rationale. BMC Biology, 16(1), 53.
Farming the mitochondrial ancestor as a model of endosymbiotic establishment by natural selection.
Zachar, I., Szilágyi, A., Számadó, Sz., & Szathmáry, E.
The origin of mitochondria was a major evolutionary transition
leading to eukaryotes, and is a hotly debated issue. It is unknown
whether mitochondria were acquired early or late, and whether it
was captured via phagocytosis or syntrophic integration. We present
dynamical models to directly simulate the emergence of mitochondria
in an ecoevolutionary context. Our results show that
regulated farming of prey bacteria and delayed digestion can facilitate
the establishment of stable endosymbiosis if prey-rich and
prey-poor periods alternate. Stable endosymbiosis emerges without
assuming any initial metabolic benefit provided by the engulfed
partner, in a wide range of parameters, despite that during good
periods farming is costly. Our approach lends support to the appearance
of mitochondria before any metabolic coupling has emerged,
but after the evolution of primitive phagocytosis by the urkaryote.
Zachar, I., Szilágyi, A., Számadó, Sz., & Szathmáry, E. (2018). Farming the mitochondrial
ancestor as a model of endosymbiotic establishment by natural selection. Proceedings of the
National Academy of Sciences, 115(7), E1504-E1510.
