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ID: 362464.0, MPI für Evolutionsbiologie / Evolutionary ecology
Behaviour from an evolutionary point of view: experimental studies on fish and humans
Advisors:Schmid-Hempel, Paul; Milinski, Manfred
Authors:Sommerfeld, Ralf D.
Referees:Bonhoeffer, Sebastian
Date of Approval (YYYY-MM-DD):2008
Name of University:ETH
Place of University:Zürich
Physical Description
(e.g. Total Number of Pages):
134 S.
Audience:Not Specified
Table of Contents:Summary__________________________________________________________________ 7
Zusammenfassung _________________________________________________________ 10
Introduction ______________________________________________________________ 13
Sexual reproduction ____________________________________________________________ 14
Human Cooperation ____________________________________________________________ 17
Outline __________________________________________________________________ 21
Mate choice in the three-spined stickleback __________________________________________ 21
Human cooperation_____________________________________________________________ 22
Chapter 1 Seasonal Variation of Male Attractiveness in Sticklebacks ________________ 24
Abstract______________________________________________________________________ 24
Introduction___________________________________________________________________ 25
Materials and Methods __________________________________________________________ 26
Results_______________________________________________________________________ 28
Discussion____________________________________________________________________ 30
Acknowledgements_____________________________________________________________ 31
Chapter 2 Lifetime Reproductive Success and the MHC __________________________ 32
Abstract______________________________________________________________________ 32
Introduction___________________________________________________________________ 33
Material and methods ___________________________________________________________ 34
Results_______________________________________________________________________ 37
Discussion____________________________________________________________________ 41
Acknowledgments______________________________________________________________ 43
Chapter 3 Preventing Dangerous Climate Change: a Collective-Risk Social Dilemma __ 44
Abstract______________________________________________________________________ 44
Introduction___________________________________________________________________ 45
Results and Discussion __________________________________________________________ 47
Methods______________________________________________________________________ 51
Acknowledgements_____________________________________________________________ 51
Chapter 4 Gossip as an Alternative for Direct Observation ________________________ 52
Abstract______________________________________________________________________ 52
Introduction___________________________________________________________________ 53
Results_______________________________________________________________________ 55
Discussion____________________________________________________________________ 59
Materials and Methods __________________________________________________________ 61
Acknowledgements_____________________________________________________________ 63
Chapter 5 Multiple Gossip Statements, Reputation, and Trust ______________________ 64
Abstract______________________________________________________________________ 64
Introduction___________________________________________________________________ 65
Materials and Methods __________________________________________________________ 66
Results_______________________________________________________________________ 68
Discussion____________________________________________________________________ 72
Acknowledgements_____________________________________________________________ 75
Conclusion _______________________________________________________________ 76
Acknowledgements _________________________________________________________ 78
References________________________________________________________________ 80
Appendix A ______________________________________________________________ 104
Appendix B ______________________________________________________________ 106
Appendix C ______________________________________________________________ 111
Appendix D ______________________________________________________________ 122
Appendix E ______________________________________________________________ 128
Curriculum vitae__________________________________________________________ 134
Abstract / Description:Evolutionary theory based on natural selection states that individuals of a population vary
in certain traits and pass these traits on to their offspring. Furthermore, individuals
continuously compete with each other for limited resources, such as food items, mating
partners, and territories. As a consequence, those individuals that feature traits enabling them
to cope better with the current environmental conditions have an advantage in accessing and
exploiting these resources and can, therefore, allocate more resources to reproduction. Thus,
they will outcompete those individuals not having such advantageous traits and the respective
traits will spread in the population. Disadvantageous traits will diminish. The result of
evolution is ever better adapted organisms.
However, there are many traits that do not seem to be advantageous to the individual, but
they still have evolved. The present work focuses on two such phenomena that are
disadvantageous and costly at the first sight: sexual reproduction and human cooperation.
Sexual reproduction is disadvantageous, because only one half of the population can bear
offspring. Furthermore, it is costly to the individual, because, among other things, individuals
have to search for mates. It has been suggested that sexually reproducing organisms have an
advantage due to a higher genetic recombination rate. Thus, they are supposed to have an
increased ability to adapt to environmental changes. A potential source of such changes are
parasites: Organisms potentially need to continuously develop better adapted immune defence
(e.g., genes of the major histocompatibility complex, MHC) to successfully fight parasites.
This exerts selection pressure on the parasites which have to adapt subsequently. The result is
an arms race between host and parasites in which it would be advantageous for the host to
achieve a high genetic recombination rate and, hence, a high adaptability by sexual
A crucial behaviour connected to sexual reproduction is mate choice, and the threespined
stickleback is a perfectly suited model organism to investigate this behaviour in more
detail. It is known that female sticklebacks base their mating decision on various visual and
olfactory male cues, such as red breeding colouration (visual cue) and MHC peptides
(olfactory cue). Adding on to previous work, Chapter 1 deals with seasonal variation of male
olfactory attractiveness to female sticklebacks. Our results document that, besides the MHC
signal, a further cue conveys information about potential mates; male olfactory attractiveness
to females peaked in summer while the males maintained a nest. This finding suggests that
males release special substances during nest maintenance that indicate male reproductive
status to females. Evidently, female olfactory mate choice is not only based on the MHC
signal, but on a combination of at least two cues.
A second experiment (Chapter 2) examined the evolutionary consequences of mate
choice in sticklebacks under semi-natural conditions. Thereby, the focus was on MHC-based
mate choice, and actual matings were analysed in six enclosure facilities in the lake Großer
Plöner See. The obtained results are consistent with previous studies that linked MHC
genetics with fitness related traits, and show that individuals with an intermediate number of
MHC variants ultimately achieve the highest reproductive output. Consequently, choosing the
right mate bearing the best MHC genotype might confer the individual advantage needed to
cope with an ever changing environment of parasites. This finding is in line with the
hypothesis that parasite pressure is a potential cause of the evolution and maintenance of
sexual reproduction.
Another seemingly paradoxical phenomenon for evolutionary biologists is the evolution
and maintenance of cooperation. Cooperation describes behaviour that is beneficial for
another individual, but costly for the cooperator. Thus, a cooperator is someone who invests
his own resources in order to help others. Evidently, a defector (i.e., someone who does not
cooperate) does not bear the costs of cooperation and, therefore, has more resources to
himself. But why is cooperative behaviour so abundant if it is costly? This is especially
puzzling in the case of humans which tend to cooperate even with unrelated individuals in
one-shot encounters.
In general, university students played computer-based games that served as experimental
setup for the research presented in the second part of this thesis. Analysing the participants’
behaviour provided further insight into the phenomenon of human cooperation.
A first study (Chapter 3) has elucidated whether the evolved strategies also enable
humans to solve modern social dilemmas. Thereby, we focused in Chapter 3 on a global
dilemma that we characterised as a collective-risk social dilemma: the prevention of
dangerous climate change.
To reduce the risk of dangerous climate change, greenhouse gas emissions need to be
reduced to ~50% of the present level by 2050. Thus, states, companies, but also private
individuals need to invest in environmentally friendly technologies and practices. In order to
reduce greenhouse gas emissions down to a certain threshold, we need to invest in climate
protection up to a certain threshold. Otherwise we will face substantial human, ecological, and
economic losses. This scenario was simulated in an experimental game with 30 groups of six
students each. The participants’ investments in climate protection had to reach a known
threshold to prevent dangerous climate change. Participants only reached this threshold if the
risk of personal loss was high. Thus, we conclude that humans are able to solve the real
climate dilemma if they are convinced about the extreme risk of losses.
Further experiments on cooperation (Chapters 4 and 5) are based on the finding that
humans tend to direct their help towards people that have previously helped others. This so
called indirect reciprocity can explain high levels of cooperation and is based on the
reputation of the other person. But how do people get to know the reputation of others?
Evidently, we cannot observe all the people we possibly interact with during our entire life,
therefore various scientists proposed gossip as a possible means of spreading and gathering
this information. In this thesis, this proposed function of gossip has been investigated
experimentally. The first study in this context (Chapter 4) has shown that gossip indeed can
serve as a vector for social, reputation-relevant information. Participants described the
observed behaviour of others truthfully; this gossip was perceived as positive or negative in
accordance with the author’s intention; and, last, participants reacted on positive gossip with
cooperative behaviour, and on negative gossip with defection towards the person who was
described by that gossip. Yet, gossip also seems to have a strong manipulative potential;
people’s decisions were influenced by gossip designed by the experimenter even if they knew
hard facts (i.e., past behaviour) about the other person.
In a follow-up study (Chapter 5), this effect was examined in more detail. The effect of
multiple gossip statements was examined with respect to elicited cooperation from the people
encountering them. The participants’ response was compared to the same people’s response
based on a single gossip statement or direct observation. The results indicate that an increased
number of gossip statements helps to reduce the risk of manipulation and to direct cooperative
behaviour towards cooperators. Furthermore, this study suggests a strong connection between
reputation, reciprocity, and trust: Participants who gained a high reputation through
reciprocating were also perceived as more trustworthy. This connection might have fostered
cooperative behaviour up to the present level in modern human societies. These findings
support the hypothesis that gossip and, hence, the use of language, is connected to the high
level of human cooperation.
Document Type:PhD-Thesis
Affiliations:MPI für Evolutionsbiologie/Abt. Evolutionsökologie
Relations:Is Version Of-EDOCID:351047
Is Version Of-EDOCID:330169
Identifiers:LOCALID:Diss/12003 [Signatur/Zugangsnummer]
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