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2The Concept of Herd Behaviour: Its
Psychological and Neural Underpinnings
Tatsuya Kameda, Keigo Inukai, Thomas Wisdom, and
Wataru Toyokawa*

In an increasingly connected world, an event in one place, be it economic, political, or social, can cause large-scale chain reactions across many other places. We
have abundant examples of this sort, including the recent global financial crisis,
the spread of civil uprisings in the Middle East, the widespread success of technological innovations such as the iPad, and so on. Until recently, such mass phenomena have been studied rather sporadically in various social science disciplines
without much mutual communication. Yet with advances in technology and newtheoretical frameworks, these mass phenomena are becoming a focus of substantive interdisciplinary interests.1 An umbrella concept, ‘herding’, has facilitatedsuch cross-disciplinary communication over the last five years.

I. Herd Behaviour: A Definition and Examples
What is meant by herding? Herding refers to an alignment of thoughts or behaviours of individuals in a group. Most importantly, such convergence often emerges
through local interactions among agents rather than some purposeful coordination by a central authority or a leading figure in the group. In other words, theapparent coordination of the herd is an emergent property of local interactions.2
Textbook examples of herding in the social science literature include riots,
panics, fads, mass hysterias, urban legends, economic bubbles, and so on.3
However, besides these familiar examples, recent research suggests that herding* All at Hokkaido University, Department of Behavioural Science.
1 Eg G. A. Akerlof and R. J. Shiller, Animal Spirits: How Human Psychology Drives the Economy,
and Why It Matters for Global Capitalism (Princeton, NJ: Princeton University Press, 2009).
2 R. M. Raafat, N. Chater, and C. Frith, ‘Herding in Humans’ (2009) 13 Trends in Cognitive
Sciences 420–8.
3 See N. J. Smelser, Theory of Collective Behaviour (Glencoe, Illinois: Free Press, 1963); R. H. Turnerand L. M. Killian, Collective Behaviour (Englewood Cliffs, NJ: Prentice-Hall, 4th edn, 1993).

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may encompass a much wider range of our social behaviours than had been previously thought.

1. Crimes
The proliferation of crimes in a city may be seen as an example of herding. Oneof the most striking aspects of crime is that crime rates vary remarkably acrosstime and space. For example, homicide rates across nations in 1990 ranged from
6.1 cases per million in Japan, to 12.6 in Sweden, to 98.0 in the United States.
Within the United States, rates of serious crimes in the year ranged from 0.008
per capita in Ridgewood Village, New Jersey to 0.384 in nearby Atlantic City.4
Such high variances are observed within cities as well, where one street can havemuch higher crime rates than streets just a few blocks away.
One obvious explanation for such high variances may be that socio-economic
conditions also vary over time and space, creating temporal and geographicalclusters of crime. However, an econometric analysis by Edward Glaeser and others showed that less than 30 per cent of the variation in cross-city or cross-district
crime rates could be explained by the local socio-economic differences. These
researchers developed a model in which agents’ decisions about crime were afunction of their own attributes (eg, socio-economic as well as psychologicalattributes) and of their neighbour’s decisions about criminal activities. Glaeser
and others then estimated impacts of the second element of the model (ie, social
influence from neighbours) for a variety of crimes in the United States in 1985, in
1970, and across New York City in 1985. The overall results showed that positive
interaction among agents’ decisions about crime was the only viable explanation
for the large residual variance not explainable by the local socio-economic conditions. More specifically, the local social influence was strong for larceny and auto
theft; moderate for assault, burglary, and robbery; and weak for arson, murder,
and rape. These results suggest that one agent’s decision to commit crimes (relatively minor crimes in particular) affects his or her neighbour’s decisions, whichconstitutes a positive feedback loop as a whole. The large variations in crime rates
across time and space seem to emerge as aggregated outcomes of such individual
local decisions.

2. Obesity
Recent research suggests that obesity may be contagious as well.5 Using a data
set from a longitudinal survey on cardiovascular disease (the Framingham
Heart Study),6 Nicholas Christakis and James Fowler examined how social
4 E. L. Glaeser, B. Sacerdote, and J. A. Scheinkman, ‘Crime and Social Interactions’ (1996) 111
Quarterly Journal of Economics 507–48.
5 N. A. Christakis and J. H. Fowler, ‘The Spread of Obesity in a Large Social Network over 32
Years’ (2007) 357 New England Journal of Medicine 370–9.
6 See <http://www.framinghamheartstudy.org/>.

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The Concept of Herd Behaviour: Its Psychological and Neural Underpinnings 63
relations in a community affect obesity. The original survey traced health statesof people residing in Framingham, Massachusetts over 32 years. Christakis andFowler focused on family or friendship relations among the participants, andapplied longitudinal statistical models to examine whether weight gain in one
person was associated with weight gains in his or her friends, siblings, spouse,and neighbours.
Results of the network analysis revealed that obese people (defined as thosewith a Body Mass Index greater than 30) and non-obese people formed different clusters and that social influences through the network extended up
to three degrees of separation. In other words, the average obese person was
more likely to have obese friends, friends of friends, and friends of friends offriends than was the average non-obese person. Moreover, a person’s chances of
becoming obese increased by 57 per cent if he or she had a friend who became
obese in the time period, by 40 per cent if a sibling became obese, and by 37
per cent if a spouse became obese. These patterns suggest that obesity spreads
through social network like a pathogen. Another person’s overeating behaviour
affects one’s overeating behaviour through the social network, even if he or
she does not know the person directly. Segmentations of obese and non-obese
people in a community seem to emerge as aggregated consequences of such
local influences.

3. Happiness
Happy people and unhappy people also seem to inhabit different clusters in acommunity. A reanalysis of the Framingham Heart Study data set suggested thatthese clusters did not simply reflect a tendency for individuals to associate withsimilar individuals. Instead, these macro patterns resulted from spread of happiness and unhappiness through the social network, just as in the case of obesity.
According to the analysis, the probability that one was happy increased by 25 percent if a friend who lived within a mile became happy, and these local influences
also extended up to three degrees of separation. Thus, like obesity, happiness also
seems to be contagious.7

II. Why Does Herding Occur? Potential Mechanisms
The examples earlier suggest that herding is a robust phenomenon, characterizing
a wide range of social behaviours in our life. If so, what are the neural, psychological, or sociological mechanisms that produce herding? This Section reviews
potential mechanisms that are thought to underpin herding behaviour.

7 J. H. Fowler and N. A. Christakis, ‘Dynamic Spread of Happiness in a Large Social
Network: Longitudinal Analysis over 20 Years in the Framingham Heart Study’ (2008) 337 British
Medical Journal 2338.

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1. Emotional contagion, facial mimicry, and mirror neurons
As implied by the saying that your smile makes others happy, humans often reproduce others’ emotions in themselves. This phenomenon, which is called emotional
contagion,8 has long been known among psychotherapists who treat depressedclients. Therapists, especially those who are inexperienced, are sometimes ‘caught’by their clients’ emotions, expressed during interviews, and feel themselvesdepressed afterwards. Elaine Hatfield and her colleagues see emotional contagion as a primitive, automatic, and unconscious process, and argue that it occurs
through a series of steps: when a receiver is interacting with a sender, he or she
first perceives the emotional expressions of the sender. The receiver then automatically transfers the perceived emotional expressions to his or her bodily expressions(eg, facial expressions, postures). Through the process of afferent feedback, thesecopied bodily expressions are translated into the receiver feeling the same emotionthat the sender experienced, which leads to emotional convergence between thesender and the receiver.
Indeed, it can easily be demonstrated that we have a tendency to mimic
the facial expressions of others in everyday social interactions. Research suggests that such facial mimicry is an automatic, reflex-like process, in which theobserver’s facial expression matches the observed facial expression (eg, happy,
sad, fearful, angry, disgusted faces) rather quickly—typically within less thana second.9 Such automatic mimicry extends to bodily posture, voice pitch, andso on, and is known to emerge very early in human development. Even 12- to
21-day-old infants can imitate both facial and manual gestures displayed by an
adult model.10
Furthermore, recent developments in neuroscience suggest that there may be
a system in our brains that helps us to mirror others’ actions. One of the mostimportant recent findings in brain science is the discovery of ‘mirror neurons’.
In the late 1980s when Giacomo Rizzolatti and others were recording electricalactivity in the brain of a macaque, these researchers found neurons that fired bothwhen the animal acted and when the animal observed the same action performedby another. The same neurons fired when the monkey grasped something with
its hand, and when the monkey observed the experimenter grasping it; however,these neurons did not discharge in response to simple presentation of food or ofother interesting objects. The neuron ‘mirrored’ the motor behaviour of the other,
8 E. Hatfield, J. T. Cacioppo, and R. L. Rapson, Emotional Contagion (New York: Cambridge
University Press, 1994).
9 U. Hess and S. Blairy, ‘Facial Mimicry and Emotional Contagion to Dynamic Emotional
Facial Expressions and their Influence on Decoding Accuracy’ (2001) 40 International Journal of
Psychophysiology 129–41.
10 A. N. Meltzoff and M. K. Moore, ‘Imitation of Facial and Manual Gestures by Human
Neonates’ (1977) 198 Science 75. This finding was replicated with neonatal chimpanzees, our closest relatives. At less than seven days of age, the chimpanzees could imitate human facial gestures(tongue protrusion and mouth opening): M. Myowa-Yamakoshi, M. Tomonaga, M. Tanaka, andT. Matsuzawa, ‘Imitation in Neonatal Chimpanzees (Pan Troglodytes)’ (2004) 7 Developmental
Science 437–42.

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The Concept of Herd Behaviour: Its Psychological and Neural Underpinnings 65
as though the observer were in fact executing the motor act. Although it remains
controversial, some recent data suggest that a similar ‘mirror neuron system’ may
exist in human brains as well.11
Taken together, these psychological, behavioural, and neural findings strongly
suggest that aping others may be a fundamentally human activity.

2. Social norms, mutual expectations, and shared stories
Another mechanism for herding involves more conscious, deliberate, or controlled
psychological processes, which are distinguishable from our automatic ‘aping’ propensities as reviewed earlier. These processes have been studied mainly by social
psychologists.
Classic experimental demonstrations of such herd behaviours in social psychology
include the famous line-comparison study by Solomon Asch where subjects conformed to an erroneous majority view to avoid potential embarrassment or othersocial sanctions in a group;12 the optical illusion study by Muzfer Sherif demonstrating that individual perceptions of the illusion converged on a shared social reality (ie,everybody in the same group ended up seeing the identical optical illusion) throughcommunication;13 and so on.
A key element underlying these herd behaviours is a fundamental characteristic of
our mind, which may be termed ‘docility’ or receptivity to social norms.14 Herbert
Simon defined this concept as our tendency to depend on others’ suggestions, recommendations, persuasion, and information obtained through social channels as amajor basis of choice.
Compared to other gregarious species, humans are unique in developing social
norms and mutually shared expectations, which inform us about what action isnormal, appropriate, or just in a given social situation. As seen in the Asch experiment, the human mind is built to be highly receptive to social norms, and tends toself-censor actions in advance in order to avoid deviating from norms.15 The humanmind is also built to think in terms of, and be influenced by, narratives or stories(sequences of events with an internal logic and dynamics).16 Stories, especially stories

11 G. Rizzolatti and L. Craighero, ‘The Mirror-Neuron System’ (2004) 27 Annual Review of
Neuroscience 169–92.
12 S. E. Asch, ‘Studies of Independence and Conformity: A Minority of One against a Unanimous
Majority’ (1956) 70(9) Psychological Monographs.
13 M. Sherif, The Psychology of Social Norms (New York: HarperCollins, 1936).
14 H. A. Simon, ‘A Mechanism for Social Selection and Successful Altruism’ (1990) 21 Science
1665–8; T. Kameda and R. S. Tindale, ‘Groups as Adaptive Devices: Human Docility and Group
Aggregation Mechanisms in Evolutionary Context’ in M. Schaller, J. A. Simpson, and D. T. Kenrick(eds), Evolution and Social Psychology (New York: Psychology Press, 2006) 317.
15 Notice that the high receptivity to social norms is also fundamental to our ability to learn
culturally. Humans are a cultural species that can take full advantage of socially-acquired knowledge. Without ‘docility’ by learners to their ‘cultural parents’, however, such cognitive capacities
would be highly limited. See M. Tomasello, The Cultural Origins of Human Cognition (Cambridge,
Mass: Harvard University Press, 1999).
16 R. C. Shank and R. P. Abelson, Scripts, Plans, Goals and Understanding (New York: Wiley, 1977).

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shared in a community or across a whole society, lead us to see, interpret, have feelings about, and react to things from the shared viewpoint.17
This characteristic receptivity of individual minds can yield effects that are
visible at the societal level. In the aforementioned case of contagious obesity, forexample, one may decide to eat more because the action seems to be normal given
one’s spouse’s or friend’s eating practices, which in turn provides a normative
stage for another’s overeating. Our actions have spill over effects (which economists often call externalities) on others, which can lead to spiralling proliferationsof action across a whole society.18

3. Rational conformity and information cascades
Sometimes it is rational to conform to majority behaviour in a group, even if one
would otherwise choose differently. Hans Christian Andersen’s ‘The Emperor’s
New Clothes’ provides a case in point. To recall, an Emperor who cares greatly
about his appearance and attire hires two tailors who promise him the finest suitof clothes made from a fabric invisible to anyone who is unfit for his position or‘just hopelessly stupid’. The Emperor cannot see the cloth himself, but pretends
as if he can for fear of appearing unfit for his position or stupid, and is joinedin this pretence by his ministers, subordinates, and general citizens. Notice thatthe ‘spiral of silence’19 occurs because it is rational to keep quiet given another’ssilence. Standing up to tell the truth is risky given a possibility (even if it may besmall) that the cloth may be visible to another’s eyes. And if such a perception
holds for everybody simultaneously,20 this constitutes an equilibrium where any
unilateral deviations (seem to) work against the deviator. A bank run which is
initially triggered by some groundless rumour provides a similar example, wherethe (ungrounded) prophecy of bankruptcy can be self-fulfilling through a positive
feedback loop.21
Information cascades are another example of rational conformity. An information cascade occurs when it is optimal for an individual who has observed the‘consensus’ actions of preceding others to follow the predecessors’ actions regardless of the private information that the individual has. Sushil Bikhchandani andothers illustrated this process by an example of a paper submission to an academic
17 See G. A. Akerlof and R. J. Shiller, Animal Spirits: How Human Psychology Drives the Economy,
and Why It Matters for Global Capitalism (Princeton, NJ: Princeton University Press, 2009) forinteresting recent examples of influential political-economic stories.
18 M. Granovetter, ‘Threshold Models of Collective Behaviour’ (1978) 83 American Journal of
Sociology 1420–43.
19 E. Noelle-Neumann, The Spiral of Silence: Public Opinion – Our Social Skin (Chicago: Universityof Chicago Press, 1993).
20 This situation is called pluralistic ignorance in social psychology: a majority of group members
privately reject a norm, but assume (incorrectly) that most others accept it. In other words, thisis a situation where no one believes, but everyone thinks that everyone else believes. See D. Katz
and F. H. Allport, Students’ Attitudes: A Report of the Syracuse University Reaction Study (Syracuse,
NY: Craftsman Press, 1931).
21 R. K. Merton, Social Theory and Social Structure (New York: Free Press, 1968).

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journal. A referee in a first journal reads the submitted paper, assesses its quality, and makes a decision about whether to accept or reject it. Suppose that areferee at a second journal learns that the paper was rejected by the first journal.
Assuming that the referee cannot evaluate the paper’s quality perfectly, knowledge of the previous rejection should make the referee lean toward rejection. If
the paper is rejected at the second journal, this process can continue at otherjournals, yielding a chain of rejections. Economists proposed a model which
proved that, at some stage in a sequential-choice setting, a rational Bayesian
decision-maker should ignore his or her private information and act only on
the public information obtained from previous decisions. Once this stage isreached, all decision-makers thereafter in the sequence should do the same,yielding an information cascade.22 And if the earlier decisions in the sequence
happen to be erroneous (eg, rejecting a high-quality paper), the cascade leads toundesirable outcomes.
Information cascades have been studied mainly by economists,23 and areoften associated with various herd behaviours in financial markets, legal
decision-making,24 and so on.

III. Herding and the Wisdom of Crowds
The mechanisms reviewed earlier, ranging from unconscious, automatic mimicry to more reasoned, deliberate conformity to rational herding, are fundamental building blocks of mass or group phenomena. The robustness of thesemechanisms, which underlie a wide range of our social behaviours, raises a
central question about the nature of herding: is herding always problematic,
as is often implied by some popular images (eg, mass hysterias, mobs, panics,
fads, economic bubbles, groupthink, etc)? This question becomes clear if we
consider ‘the wisdom of crowds’, a totally different notion of group behaviour,
popularized by James Surowiecki.25 While herding in humans often refers to
defective social processes that degrade toward suboptimal performance, thewisdom of crowds implies highly intelligent group processes that can leadto collective wisdom. How can we reconcile the two contrasting images ofcollectivities?

22 S. Bikhchandani, D. Hirshleifer, and I. Welch, ‘A Theory of Fads, Fashion, Custom, andCultural Change as Informational Cascades’ (1992) 100 Journal of Political Economy 992–1026;
A. V. Banerjee, ‘A Simple Model of Herd Behaviour’ (1992) 107 Quarterly Journal of Economics
797–818.
23 For reviews of laboratory studies, see L. R. Anderson and C. A. Holt, ‘Information Cascade
Experiments’ in C. R. Plott and V. L. Smith (eds), The Handbook of Experimental Economics Results(Amsterdam, New York, Oxford, Tokyo: North Holland, 2008) 335–43.
24 W. Farnsworth, The Legal Analyst: A Toolkit for Thinking about the Law. (Chicago: Universityof Chicago Press, 2007).
25 J. Surowiecki, The Wisdom of Crowds: Why the Many are Smarter than the Few and How
Collective Wisdom Shapes Business, Economies, Societies and Nations (New York: Doubleday, 2004).

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1. Group decision-making by honeybees
To consider this question, it seems useful to extend our scope to include herd
behaviour by non-human animals that also live collective lives. Althoughhumans are a gregarious species, we are arguably not the most gregarious
species of all. Our rivals in this respect are eusocial animals, including bees, ants,
termites, naked mole rats, etc. Eusocial species are colonial animal species thatlive in multigenerational family groups, in which the vast majority of individuals
cooperate to aid relatively few reproductive group members. They often exhibit
extreme task specialization, which makes colonies potentially very efficient ingathering resources.
The puzzle of these species is how they can achieve such high efficiencies collectively, despite the fact that they have relatively much smaller brains as comparedto humans. More specifically, how do they avoid defective social processes leading
to problematic herd behaviour? We will examine group decision-making by honeybees to address these questions.
In late spring or early summer, as a large hive outgrows its nest, a colony of honeybees often divides itself. The queen leaves with about two-thirds of the worker
bees to create a new colony, and a daughter queen stays in the old nest with therest of the worker bees. The swarm leaving the colony must find a new home
in a short time, which is critical to their survival. The leaving swarm, which iscomposed of 10,000 or so bees, typically clusters on a tree branch, while several
hundred scout bees search the neighbourhood for a new home. These scout bees
fly out to inspect potential nest sites, and, upon returning to the colony, perform
waggle dances to advertize any good sites they have discovered. The duration of
the dance depends on a bee’s perception of the site’s quality: the better the site, thelonger the dance. Other scout bees that have not flown out yet, as well as thosethat have stopped dancing, observe these dances and decide where to visit. In
these decisions, the bees are more likely to visit and inspect the sites which havebeen advertized strongly by many predecessors. This process constitutes a positive
feedback loop. Thomas Seeley and others, who conducted a series of experimentswith honeybees in natural settings, found that the bees usually could choose thebest nest site. Even though none of the bees visits all the potential nest sites individually, they can aggregate partial individual information to form a collective
wisdom that enables high-quality decisions.26
Although the bees’ performance is highly impressive, the puzzle still remains. How
do the bees solve the problem of interdependency? As we have seen earlier, the bees
communicate their findings via waggle dances which are performed sequentiallyby scout bees. This could create statistical dependencies among decision-makers,
in which initial errors committed by earlier scouts can carry over and be amplified
in the sequence. In this sense, the honeybee group decision-making system may
be susceptible to the erroneous information cascade.
26 T. D. Seeley, Honeybee Democracy (Princeton, NJ and Oxford: Princeton University
Press, 2010).

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A recent article has addressed this question theoretically via a computer simulation model. In line with the previous empirical observations, the model assumes
that scout bees are dependent on other bees in that they give more attention tonest sites strongly advertized by their predecessors. The bees essentially conformto a majority view in their decisions about where to visit. But, simultaneously, themodel assumes that the bees are independent in assessing the quality of the visitedsite. The duration of the scout’s dance, which indexes the strength of the bee’s
preference for the site, is not affected by others’ waggle dances, but determinedsolely by her own perception of the site’s quality. The computer simulation results
showed that, when a suitable mixture of influence and independence exists, thehoneybee group decision-making process works well.27

2. Collective wisdom on the Internet?
Honeybee nest search provides an impressive example of how animals that have
only limited cognitive capacity as individuals can make ‘wise’ decisions collectively as a swarm. It is also important to note that the ‘swarm intelligence’28 inhoneybees emerges not from some purposeful coordination by a central authority(eg, the queen), but through local interactions among the bees—a key elementin the definition of herding as discussed earlier in this Chapter. Interestingly,
the honeybee nest-search situation seems to have similar counterparts in modern
human societies, where individuals can use public information as well as private
information to make a well-informed decision. Examples include information
searching on the Internet when buying books or music, choosing a restaurantfor dinner, deciding which hotel to stay at, and so on. Potential options are quite
large in number, yet our time budget for private information searches is limited. In these occasions, we often visit relevant websites (eg, Amazon, Yelp) to
see how others have decided. Do these social information pooling systems on
the Internet, in which individuals informed by predecessors’ experiences reporttheir own new experiences to share with others, yield collective wisdom as in thehoneybee case?
A recent experiment on a ‘cultural market’ by Matthew Salganik and others focuses on this point.29 In cultural markets, sales volumes of hit songs,
books, and movies are many times greater than average. This may imply that‘the best’ alternatives are qualitatively different from ‘the rest’, yet experts
routinely fail to predict which cultural products will succeed. Why does thisfailure occur?

27 C. List, C. Elsholtz, and T. D. Seeley, ‘Independence and Interdependence in Collective
Decision Making: an Agent-based Model’ (2009) 364 Philosophical Transactions of the Royal Society
B 755–62.
28 J. Krause, G. D. Ruxton, and S. Krause, ‘Swarm Intelligence in Animals and Humans’ (2009)25 Trends in Ecology and Evolution 28–34.
29 M. J. Salganik, P. Sheridan Dodds, and D. Watts, ‘Experimental Study of Inequality andCultural Market’ (2006) 311 Science 854–6.

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Intrigued by the unpredictability of cultural markets, these researchers createdan experimental music market, where a total of 14,341 participants downloaded
previously unknown songs under one of two conditions—the ‘social influence’
condition or the ‘independent’ condition. In both conditions, participants could
listen to any song they were interested in to have a direct experience of the product. On top of the individual learning opportunity, participants in the ‘social
influence’ condition were provided social information about how many times
each song had been downloaded by previous participants. Notice that there was astructural similarity between the social influence condition and the honeybee nest
search situation. In both situations, agents had to make choices between unfamiliar options that could differ in quality. Also, when making individual decisions,social frequency information (predecessors’ behaviours) was available, in addition
to the opportunities for individual information search.
The experiment revealed several interesting results. First, inequality in overall
download counts among songs was much greater in the social influence condition, as compared to the independent condition in which participants could notaccess to the social-frequency information. Obviously, participants in the social
influence condition copied predecessors’ choices, which yielded a ‘rich get richer’outcome. Thus, the experiment replicated the robust phenomenon in cultural
markets that hit songs are many times more successful than average.
Secondly, the most popular song (with the highest download frequency) in the
independent condition did not necessarily correspond to the most popular ones inthe social influence condition. Mapping of the songs in terms of popularity ranking between the two conditions was at most moderate—the most popular song in
the independent condition never did very badly in the social influence condition,and the least popular song never did extremely well either. However, almost anyother result could happen. The success of a song in the social influence condition
was path-dependent and susceptible to random fluctuations, which may explain
why it is difficult for even experts to predict which products will succeed in cultural markets.
Overall, how did the human performance in the experimental music market
compare to the honeybee performance in the nest search? A tentative answer does
not seem to be favourable to us. Honeybees mix dependence and independence
in the nest search. They conform to predecessors to decide which sites to visit, but
assess the quality of the visited sites independently from predecessors’ evaluations.
This leads to the typical swarm’s high performance. On the other hand, humanparticipants in the experimental music market seemed to fail to separate the two
aspects and rely too much on others’ choices. Of course, the inherent subjectivity of music preferences means that the quality of experimental cultural market
outcomes cannot be assessed objectively (as the nest choice decisions can). Yet,the lack of correspondence in song-popularity between the independent and thesocial influence conditions suggests that such subjective preferences are unstableand fragile. In this sense, the hyper-susceptibility of mass behaviour to social
influence is problematic not only for marketers of cultural products, but also inmany socio-political domains where no demonstrably correct answer exists.

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IV. Conclusion
In this Chapter, we have reviewed various manifestations of herding in humans.
As we have seen, humans are a highly socially receptive species, as compared withother gregarious animals. Accumulating evidence in various behavioural science
disciplines strongly suggests that we humans are equipped with neural, psychological, and behavioural mechanisms that underpin this receptiveness—our abilities to learn from and be influenced by others. It is no doubt that these built-in
mechanisms are evolutionary products that have served our survival and fundamentally contributed to our adaptive success on the earth. Yet, these adaptive
tools can cause serious errors in modern environments, in which interconnectivities of individuals are much denser and externalities accruing from individual
behaviours are much greater and more far-reaching, as compared to ancient environments in which the human mind evolved.
Interestingly, growing evidence in the behavioural sciences also seems to suggestthat the two contrasting collective phenomena in humans—maladaptive herding
and the wisdom of crowds—are underpinned by similar basic mechanisms. In
this sense, the two apparently opposite macro phenomena may be seen as twins
produced and governed by the receptivity of our minds. Given this commonality,
understanding the neural, psychological, and behavioural mechanisms that could
help distinguish these twins will be one of the most important challenges forbehavioural sciences in the next decade.30

30 For further discussion, see T. Kameda, T. Tsukasaki, R. Hastie, and N. Berg, ‘Democracy
under Uncertainty: The Wisdom of Crowds and the Free-Rider Problem in Group Decision
Making’ (2011) 118 Psychological Review 76–96.

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