Information Flows in Computational Approaches to the Evolution of Cooperation

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Information Flows in Computational Approaches to
the Evolution of Cooperation

• Timothy A. Kohler
• Department of Anthropology
• Washington State University
• Pullman, WA 99164-4910 USA
• tako_at_wsu.edu

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Plan

• What is information?
• How information functions in various
  computational approaches proposed to understand
  the problem of human cooperation
• Simple, easy-to-understand systems
• Structure of such problems isor can be recast to
  becomewhy people forego immediate personal gain
  to pursue prosocial, longer-term goals that might
  include achieving a sustainable but still
  high-payoff interaction with the environment

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Information (1)

• Intrinsic component of all physical systems?
• Flows, but cannot fill up an empty container
• Claude Shannon developed techniques for measuring
  the information rate of a source and the capacity
  of a channel
• Others argue that information itself has zero
  dimension and that therefore, like contrast,
  symmetry, correspondence, etc., cannot be
  located (Gregory Bateson)

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Information (2)

• Just as mass is a reflection of a system
  containing matter, and heat is a reflection of a
  system containing energy, organization is the
  physical expression of a system containing
  information.
• Just as energy has as one of its fundamental
  attributes the capacity to perform work,
  information has as one of its fundamental
  attributes the capacity to organize things.

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Information (3)

• Information is the raw material which, when
  information-processed, may yield a message. Upon
  receipt of a message, the message must once more
  be information-processed by the recipient for the
  message to acquire meaning.
• There are many different kinds of
  information-processing systems (ISPs) for
  example, the thermostat is a mechanical ISP
  computers are electronic ISPs brains are
  neurological ISPs.

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"Lineages" or "flow structures" of information
occur in three domains that form a nested
hierarchy (Goonatilake 1991)

• the genetic
• the neural-cultural (including individual memory
  and cognitive process, which I consider useful to
  separate from culture and its transmission)
• and the "extrasomatic" (artifacts, especially
  information storage devices).

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Cooperation Sharing

• Two large classes of contemporary approaches to
  understanding altruism
• unselfish behaviors are really disguised selfish
  behaviors
• truly unselfish behaviors have been able to
  evolve through genetic or cultural group
  selection
• A behavior is altruistic when it increases the
  fitness of others but decreases the fitness of
  the actor.

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Kin Selection

• Genes are the fundamental units of reproduction,
  and we are only vessels for our genes
• We therefore ought to be molded by evolution to
  assist our closest relatives preferentially
• Philip Morin et al. (1994) have demonstrated that
  such cooperative behaviors among chimp males as
  defense of territory and political support to
  achieve alpha male status seem explicable through
  principles of kin selection
• Unarguable, but incomplete

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(Direct, Pairwise) Reciprocal Altruism

• Classic IPD role of information extremely
  constrained
• In memory-1 strategies such as TFT, the only
  information one player has about the other is
  whether that player cooperated or defected in the
  past move.

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Lindgren Nordahl

• possibility of the initially neutral evolution of
  strategies with longer memory
• for example, a memory 2 strategy would remember
  both an opponent's and self's prior moves,
  allowing for the appearance of more complicated
  strategies
• longer-memory strategies have an advantage

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Characteristics of Pairwise Reciprocity

• In 2-person games cooperation may emerge through
  selection in evolutionary games if pairs of
  individuals interact for a sufficient number of
  times, often leading to something generically
  similar to a Tit-for-Tat strategy
• Populations composed of unconditional defectors
  can resist invasion by reciprocators unless there
  is some degree of assortative pairwise interaction

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Problems with Pairwise Reciprocity

• When groups are larger than 2 are formed at
  random, however, and the play is structured as an
  n-way prisoner's dilemma, reciprocating
  strategies become increasingly less likely
• Groups of 32 expecting to have about 1,000
  interactions must have initial frequencies of
  some 70 reciprocators for cooperative strategies
  to increase (Boyd and Richerson 1988)

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Indirect Reciprocity

• Pairs of players who encounter each other
  infrequently
• Changes information that players have about each
  other in an important fashion
• One well-known formalization due to Nowak and
  Sigmund (1998)

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Nowak and Sigmund (1)

• Random pairs of players are drawn from a
  population, one of whom is a potential donor and
  the other a potential recipient
• Donor can cooperate and help the recipient at a
  cost c to himself, in which case the recipient
  receives a benefit of value b (bgtc)
• If the donor decides not to help, both
  individuals receive zero payoff

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Nowak and Sigmund (2)

• Each player has an image score, s, which in some
  games is visible to all players
• If a player chosen as a donor chooses to help,
  her image score increases by 1 if she chooses
  not to help, her image score is decreased by one
  unit (the image score of a recipient does not
  change in either case)

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Nowak and Sigmund (3)

• Players have various strategies for helping and
  decide to help based on a threshold k if the
  recipients image score (s) is greater than k they
  help, if not, they dont
• Players with the highest scores (the payoffs from
  playing, not the image scores) at the end of a
  round produce offspring in proportion to their
  scores

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Nowak and Sigmund (4)

• When everyone's image can be seen by each player,
  and when there is no mutation, the population is
  quickly dominated by players with a k0 strategy
  (they will cooperate with anyone who has an image
  score of 0 or better)
• the most discriminating of all the cooperative
  strategies
• Under mutation and selection, strategies cycle
  endlessly

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Indirect Reciprocity (concluded)

• If players have information about the degree of
  other players' propensities to cooperate, and
  make judgments about whether to cooperate based
  on that "reputation," cooperation is easier to
  sustain, even in large groups, so long as these
  "reputations" are widely known
• Some recent empirical work (Wedekind and Milinski
  2000) suggests that people do not necessarily
  focus their altruistic acts on those who have
  been kind to others, calling into question the
  mechanism proposed here
• Cognitive burdens?

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Costly Signaling (1)

• Some similarities to previous approach signals
  that are costly to the emitter constitute
  information used by a recipient in choosing an
  action, such as whether or not to cooperate with
  the signaler
• But here, signal is connected to some underlying
  but poorly observable quality of the signaler
  which nevertheless is of importance to the
  receiver
• Also, signaler is providing a public benefit
  through his or her signalfor example, turtle
  hunting among the Merriam (Smith and Bliege Bird
  2000)

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Costly Signaling (2)

• Prosocialor any other type ofsignaling is a
  Nash equilibrium if
• low-quality types pay greater marginal costs for
  signaling than do high-quality types
• other group members benefit more from interacting
  with high-quality than with low-quality types
• other group members benefit more from interacting
  with high-quality than with low-quality types
  (Smith, Bowles, and Gintis 2000)

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Costly Signaling (3)

• If the reason that indicator traits of underlying
  qualities are often "prosocial" (enhancing the
  well-being of members of Ego's social group
  beyond his or her immediate kin) is that
  pro-social traits are valued in and of themselves
  (since they signal the signaler's value as a
  potential ally) then the line between CST and
  indirect reciprocity based on image scoring is
  extremely fine

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Apparent Altruism (Concluded)

• Except perhaps for indirect reciprocity through
  image scoring, any of the pathways to cooperation
  considered above employ mechanisms that would be
  as available to other animals as to humans
• Seminal contributions to reciprocal altruism and
  costly signaling were by biologists (Trivers, and
  Zahavi and Grafen, respectively)

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Strong Reciprocity and Multilevel Selection (1)

• Relies on a cultural information channel
• A form of altruism that benefits group members at
  a cost to the strong reciprocators, and involves
  a predisposition to follow a social norm to
  cooperate with others and punish non-cooperators
• Defined to contrast with reciprocal altruism
  which is considered "weak reciprocity" because it
  is so dependent on high probabilities for future
  interaction
• Result is truly unselfish behavior, not disguised
  selfish behavior

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Necessary Requirements for Group Selection 1.
There must be more than one group (there must be
a population of groups) 2. Groups must vary in
their proportion of altruistic types 3. There
must be a direct relationship between the
proportion of altruists in the groups and the
groups fitnesses (groups with more altruists
must produce more offspring) 4. Groups must be
isolated for at least a portion of their life
cycles however, their progeny must be able to
mix or compete in the formation of new groups.
Given these conditions, group selection can be
effective if 6. The differential fitness of
groups (the force favoring the altruists) must be
strong enough to overcome the differential
fitness of individuals within groups (the force
favoring the selfish types). Sober Wilson
199826
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Strong Reciprocity and Multilevel Selection (2)

• Imagine a group of foragers, largely unrelated,
  in which agents can either work alone, or work
  cooperatively in a group, which in general is
  more rewarding.
• Output is shared equally by all agents.
• Agents may shirk, which reduces the output to be
  shared
• it is advantageous to the shirker
• if there were no policing of free riders, even
  complete shirking would promote a member's
  fitness.

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Strong Reciprocity and Multilevel Selection (3)

• Group is small enough that members can be
  monitored, and if detected shirking, may be
  punished, at some cost to the punisher.
• Punishment consists of a shirker being ostracized
  from the group.
• Ostracized agents work alone for a period before
  being readmitted to a different group.

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Strong Reciprocity and Multilevel Selection (4)

• Groups consist of two types of people
• reciprocators who work and always punish shirkers
  when they see them, even though there is a cost
  to doing so
• self-interested individuals who maximize their
  fitness and therefore never punish, and work only
  to the extent that the expected cost of doing so
  is less than the expected cost of being punished.
• Punishment consists of a shirker being ostracized
  from the group.

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Strong Reciprocity and Multilevel Selection (5)

• Analysis of fitness consequences of reasonable
  parameter settings for the costs and benefits
  shows that a stationary equilibrium can be
  expected composed of
• 70 of the population in groups (and therefore
  30 not in groups)
• these groups composed disproportionately of
  reciprocators.
• Population as a whole should be composed of 65
  reciprocators, but the groups should stabilize
  with 70 reciprocators.

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Strong Reciprocity and Multilevel Selection (6)

• To the extent that the authors hazard a
  historical reconstruction of how such processes
  might have played out in the Pleistocene, they
  favor the idea that "the cognitive and affective
  traits required to fashion, learn, detect
  violations of, and wish to uphold social norms
  may be genetically transmitted, while the content
  of the norms (and in particular the linking of
  nonshirking and punishing) may be culturally
  transmitted" (Bowles and Gintis 200116).

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Strong Reciprocity and Multilevel Selection (7)

• Useful to draw on cultureour capacity for which
  differentiates us from the rest of the animal
  kingdomto explain our propensity to live in
  highly and flexibly cooperative but largely
  unrelated groupsa practice that likewise
  distinguishes us from other animals, at least in
  degree, and does much to explain the success of
  the species.

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How do these models map into the prehistory of
human societies?
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Extremely Slow Growth in H. erectus

• erectus populations in Asia by 2 mya
• linguistic capabilities of these hominids will
  probably never be known in detail. Evolutionary
  psychologist Robin Dunbar (1996) suggests that
  language is used in three different ways
• formulaic usages with little semantic content
• gossip for passing social information
• and symbolic language of the sort employed in a
  presentation like this.

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Language uses (continued)

• Of these, the second by far dominates our
  everyday uses, and greatly facilitates the
  integration of social groups.
• Among primates, grooming is a key mechanism for
  maintaining social relationships, and grooming
  time appears to increase linearly with group size
  among the Old World monkeys and apes.
• Neocortex size relative to total brain size
  likewise scales with mean group size.

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Language uses (continued)

• If we interpolate the predicted group size for
  humans based on our neocortex size into the
  relationship between group size and grooming
  time, we find that humans would have to spend
  something in the order of 40 per cent of the day
  engaged in grooming in order to maintain
  cohesion (Dunbar 1996383).
• The earliest steps towards the development of
  language, therefore, may have been as substitute
  verbal grooming, or gossip, mitigating this time
  crisis
• Seems unlikely that language would have evolved
  beyond that point in this period

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Pre-sapiens (concluded)

• Of those mechanisms for cooperation discussed
  here, which would have been available to these
  populations?
• Certainly any but perhaps "strong reciprocity,"
  which may require greater symbolic abilities to
  understand and teach the social norms on which it
  depends

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Acceleration of population growth with the
appearance of anatomically modern humans

• 120 to 35 ka for this process (Klein 1992)
• Leading components probably include
• longer juvenile dependence and lower juvenile
  mortality
• increased provisioning of females by males with
  the development of stronger malefemale bonds and
  more exclusive mating patterns (Foley 1992)
  nuclear families?

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Leading components in transition to anatomically
modern humans (cont.)

• Longer period of juvenile dependency within the
  various families of the band provided a more
  variable, and more often one-to-one enculturation
  process that would lead to more rapid innovation
  than the strongly conservative many-to-one
  enculturation inferred for earlier times.

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Archaeology of the Upper Paleolithic

• Aggregation sites of the later Upper Paleolithic
  suggest the existence of social units that are
  too large for the participants to be related
  genetically, or perhaps even to be known to each
  other through regular face-to-face contacts.
• Such aggregations, even if only periodic, would
  have been promoted by (and may not be possible
  without) the existence of cultural norms
  dictating appropriate behavior (Chase 1994).

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Archaeology of the Upper Paleolithic (cont.)

• Many of the Upper Paleolithic symbolic activities
  seem to be ritual in nature, and ritual enforces,
  and reinforces, such norms.
• Language may have existed prior to such symbolic
  activityDunbars model predicts that social
  language (gossip) should emerge well before this
  timebut these symbolic activities must have been
  carried on through fully symbolic language.

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Archaeology of the Upper Paleolithic (concluded)

• Shared, symbolic norms may have very tangible
  consequences for individual and group survival.
• Richerson and Boyd (19926971) explain the
  origin of culture as due to its success (when
  coupled with individual learning and genetic
  inheritance) in providing a selective advantage
  in environments that are neither too constant nor
  too variable from generation to generation.

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Upper Paleolithic Societies

• Success of these populations in part due to the
  greater cooperative possibilities for large
  groups made available by strong reciprocity.
• If so, then all the mechanisms for cooperation
  considered here would have been available to
  human populations by 35 ka at the latest.

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Neolithic Societies

• What then accounts for the next feature of
  interest in population graph, the large increase
  in rate of population growth associated with
  Neolithic societies?
• Problems of organizing larger settlements and
  societies remind us that Goonatilake's third
  lineage of information"extrasomatic" artifacts,
  especially information storage deviceshas not
  been exploited in the accounts of cooperation
  presented to this point.

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External Information Storage

• Artifacts such as tokens that allowed storage of
  economic information
• Institutions that provided a framework for the
  organization of people in ways that cross-cut kin
  networks
• eventually including stratified societies that
  radically changed the egalitarian assumption of
  all the models presented above
• All were of selective value in societies that had
  grown beyond the size that could be maintained
  solely by the mechanisms discussed earlier.