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42 Cards in this Set

  • Front
  • Back
Evolution of Traits
Traits show variation--> Some trait variants are more advantageous than others-->Individuals with beneficial traits leave more offspring --> Future generations will have more individuals with beneficial traits
How do you get the evolution of complex adaptations like behavior?
basic social theory: B – C > 0
Benefit is to someone
else, cost is to you
Types of Social Interactions
Cooperation Altruism
Selfishness Spite
One-time interactions
-Non kin
-No individual recognition
ex. Prisoner’s Dilemma
With single interactions, the
solution is always to remain silent
Raven example of evolution of behavior/ complex adaptation.
Why does a young raven
announce that it’s found food?
Problem for young raven:
Territorial defense by adult raven pairs
Strength in numbers
Altruism (B1<C1) Selfish (B2>C2)
B1 + B2 > C1 + C2 = SELFISH (overall benefit is to individual
Why relationships matter
Cooperation can get you things that solitary efforts cannot...
Costly interactions can become beneficial with repeated interactions – reap long-term benefits
As a result, you would be selected to invest in
(ex. Dwarf Mongoose)
Dwarf Mongoose example of why relationships matter
Dominant female can stop
others breeding...but bigger groups do better, and subordinate animals can leave so powerful subordinates are allowed to breed
Primate sociality
Permanent bisexual groups, stable home ranges,
long-lived species, long-term relationships...
The complexity of primate social lives provides many opportunity for the formation of complex social relationships
How do behaviors like reconciliation & cooperation evolve?
natural selection maximizes fitness. measurable in 3 ways.
3 ways to measure fitness
Direct fitness
Indirect fitness
Inclusive fitness
Direct Fitness
An individuals direct fitness (DF) is measured by the number of their offspring that survive to reproduce
ex. mom has 3 offspring, each gets half her genes, so her fitness is 1 1/2
Natural Selection (fitness through relatives)
If natural selection operates through reproduction, then the winners are those that have the most genes in the world
Your relatives share
genes with you, thus
you can increase your
fitness through your
relatives as well
Determining Relatedness (r)
fitness divided by each individual in between the 2 looking at...
ex. Coefficient of relatedness between aunt/nephew?
½ * ½* ½ = 1/8 (ma, sis, neph)
Indirect Fitness
An individual’s fitness gained through relatives that pass on shared genes
Inclusive Fitness
An individual’s direct fitness PLUS fitness gained through relatives that pass on shared genes.
r is the probability that
homologous alleles present
in different individuals are
“identical by descent”
(ex. black tailed prairie dog
giving an alarm call)
Inclusive fitness
ex. black tailed prairie dog
giving an alarm call
alarm calling is costly to the caller. Alarm call nepotism in black-tailed prairie dogs - more likely to call if living with kin and acquaintances)
When Is Altruism Favored?
An allele for an altruistic
behavior will be favored if: rB > C
This is called “Hamilton’s rule”
*so requires either a very high benefit or very high coefficient of relatedness
“Hamilton’s rule”
An allele for an altruistic
behavior will be favored if: rB>C
coefficient of relatedness, B = benefit to recipient, C= cost to helper
Extreme form of kin selection in which few individuals in the group reproduce. Also characterized by reproductive division of labor, an overlap of generations and cooperative care of offspring born to the group
Eusociality in Marmosets/Tamarins
+Monogamous, polygynous or -- polyandrous
+Reproductive suppression (dominant female will surpress the reproduction in younger females behaviorally through harassment or chemically through pheromones)
+Paternal and sibling care, Chimerism (always give birth to twins, twins exchange stem cells in utero)
Hamilton’s rule helps explain how altruism between kin could evolve, but what about helping non-kin?
Reciprocal Altruism
Reciprocal Altruism
Trivers’s (1971) preconditions:
3 things needed
1) Cost to giving, benefit to receiving
2) Delay between altruistic act & reciprocated act
3) Giving is contingent upon receiving
Reciprocal Altruism
1. Individual recognition
2. Recall past interactions
3. Quantify costs & benefits
4. Recognize cheaters
5. Punish cheaters
Reciprocal Altruism
Example: Vampire Bats
"I’ll barf blood, if you’ll barf blood"
60 hrs w/out blood = dead
Individuals regurgitate blood, but to whom?
Sharing occurred with close relatives or distant
relatives with whom there was a strong association
Reciprocal Altruism
Why only weak evidence for reciprocal altruism?
Required Mechanisms:
1. Individual recognition √!
2. Recall past interactions √!
3. Quantify costs & benefits ?
4. Recognize cheaters ?
5. Punish cheaters ?
What is a “Bond”
greater then partly positive relationship
(can be positive or mixed. Not negative)
“Strong bonds”
correlation of >2 types of interaction
(Affiliation,Time together,Coalitions,Decreased
Bonds in Adults
Intersexual bonds - reproductive purposes
(Many vertebrates, mammals, birds)
Intrasexual bonds - male-male or female-female, not related to reproduction
(Primates, some carnivores,
cetaceans. No birds, fish, reptiles, or amphibians)
Coalitionary Bonds
2 types
– Coalitionary interaction = “coalition” (two indiv. help e/o out)
– Coalitionary relationship = “alliance” (long-term bond)

• Support in aggression
• Complex interactions (competition for partners)
Coalitionary Bond

“Polyadic Aggressive Interaction"
when number of individuals fight against others
*Diadic Aggression - 1 to 1 agression. If one individual cries out, then others come to help, then someone comes to support and you have 2-1 (or 3-1 or more), then you have coalition
Coalitionary Bond
Allies are often also rivals
(Females are competitive over food, Males over females)
So have to test bond
ex. Capuchin Monkeys
Coalitionary bond - Testing
ex. Capuchin Monkeys
(Trust games)
eye-ball poking
Finger in mouth
Stability of Bonds
Fixed partners
-insects or birds
Flexible partners (can change accord to rank etc.) requires greater cognitive abilities - must be able to understand others socially
-primates or cetaceans, and humans
Stability of Bonds

Rank effects
-Give support down the hierarchy
-Invest/groom up the hierarchy

Result is low-ranked
animals invest in alliances
Stability of Bonds

Flexible alliances
-Groom down the hierarchy
-Give support up the hierarchy

Competition for allies
means dominants invest
Increased affiliation after aggression (making up)

varying styles of reconciliation
– Example: macaque social styles
Example of style of reconciliation
macaque social styles
Different lineages vary in terms of friendliness dependent on different grades (grades 1"weak bonds"-4"strong bonds")
Valuable Relationship Hypothesis
Stronger bond -> High probability of reconciliation
Valuable Relationship Hypothesis
chimps vs. Macaque
Males = high prob. of rec
Females = no rec
Female = high prob. of rec
male = no rec
Reconciliation results
(before and after)
Anxiety, scratching, heart-rate, glancing
Eyes shut
is there a universal sense of fairness?
test w/ monkeys show primate understanding of fairness
ex. Rhesus Macaques
Consumers who punished were more likely to get food in subsequent trials