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Anthropology 101: Human Biological Evolution
Lecture 7: Primate Reproduction and Protoculture
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Behaviors are adaptations to particular social environments
• Behavioral strategies• Course of action under certain circumstances• Does not imply conscious reasoning, deliberate
planning, or intent• How does the behavior effect and individual’s fitness
• Costs vs. Benefits of an action
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Mammalian females are committed to invest in offspring
• Internal gestation (pregnancy)• Lactation (nursing)
• Maternal investment obligatory• Paternal care optional
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Selection shapes reproductive strategies
• Females:• Time & energy limits how often
can have new infant (reproductive success)
• Males:• Reproductive success limited by:• Number of mating opportunities
• Access to females• Range of strategies that will affect
male reproductive success• More options
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1. Males can increase RS by investing in offspring
Expect males to invest when:
1. Finding additional mates difficult
2. Fitness of kids raised by just mom is low• infants are very big• litter size > 1• high risk of
predation/infanticide
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2. Males can increase RS by competing for mates
• Sexual Selection favors traits that increase success in competition for mates
• Competition may or may not = a fight!
Two kinds of sexual selection:
• Intra-sexual selection = male-male competition for access to mates
• Inter-sexual selection = female selection of males with the most attractive traits
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Intra-sexual selection in primate males
• Male-male competition favors• Large body size• Large canines (NOT meat)• Mate guarding
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Inter-sexual selection in primate males
Inter-sexual selection = Female choice favors
• Flashy colors• Energetic displays• Friendly behavior• Paternal care
mandrill
tamarin
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Ex: Male InvestmentPair-bonded species: Marmosets & Tamarins
• Male RS tied to his mate’s RS• Males invest in offspring
• Carry infants• Share food with infants
• Males guard females vs. rivals• Closely bonded to mate
Dusky titi monkeys
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Ex: Male InvestmentPair-bonede species: Gibbons and siamangs
Males are attentive to mates
Sing duets in territorial displays
Females have priority of access
Males help care for infants
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Ex: Male CompetitionFights & distant fathers:multi-male groups
• Male RS tied to number of different females he can mate with
• Males compete for dominance rank• Favors large size & strength• Favors large canines (NOT meat)
• Rank orders change frequently
• Male rank is correlated with reproductive success
Chimps & Baboons
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Ex: Competition & InvestmentIn multi-male groups, some males provide low cost care
• Males usually tolerant of juveniles
• Males support juveniles in their fights
• Males may selectively help own offspring
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One-male groups: Competition to gain access to females is intensified
• Males compete for access to group of females• Outsiders put high pressure on resident males• Tenure of resident males often short
• VERY intense competition
• May favor infanticide under very
particular circumstances
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Infanticide: sexually-selected male reproductive strategy
• Females nurse infants for many months
• If nursing infant dies, female resumes cycling immediately
• female available for mating sooner
• If male tenure as resident male is short:
• infanticide enhances male mating opportunities
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Circumstances of infanticide
• Male takes over a one-male multi-female group or rises in rank • now has mating opportunities
for a short time
• Kill infants that are NOT their own
• Kill very young infants still nursing
• Male gets to mate with the dead infant’s mother
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Infanticide is a major cause of mortality
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Counterstrategies to thwart infanticide
• Defend victims of attack
• Mothers
• Female kin
• Males present at conception
• Fathers
• Confuse paternity
• Estrus swellings
• Mate with many males
• Mate with newcomers
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In baboons, male-female ties may prevent infanticide
• In some populations, infanticide is common when new males join group or males rise in status
• New mothers form associations with particular males
• possible father of current infant
• Males protect females’ infants
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Sexually-selected infanticide is widespread
• All the major groups of primates• Prosimians• New World monkeys• Old World monkeys• Apes
• Lions• Rodents• Birds
Many still think its pathological and not adaptive
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Controversy persists because people confuse what IS with idea of SHOULD or GOOD
• This confusion is called the “naturalistic fallacy”• assumes that natural phenomena are right, just,
unchangeable, good
• Worry that if infanticide is adaptive for langurs or lions, it would be justified in humans
• WRONG!
• We can’t extract moral meaning from behavior of other animals or what is natural.
• Culture and own choice determine right and wrong. Not nature.
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The costs & benefits of social interactions: It takes two
Actor’s Fitness Recipient’s Fitness
Selfish + -
Mutualistic + +
Altruistic - +
Spiteful - -
cooperation
easily explainedby natural selection
rare or absent innon-humans
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For altruism to evolve, must limit altruism to other altruists• Kin Selection
• Limit altruism to kin• Share genes so your
genes benefit• Focus on close kin
S. Alberts
• Reciprocal Altruism• Limit altruism to those who
help you • Alternate benefits with
partner
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How do we know who is kin?
Mothers- Learn via close
contact = familiarity- Learn about female
kin via time with mom- Siblings, aunts,
grandmother
- Fathers?
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Primates sometimes recognize paternal kin?
- Males know they mated with mom- Males know who else mated with mom
Reliability of “guess” varies • Pair-bonded species• One-male groups• Multi-male groups
If one male does 100% of mating:= father of all kids conceived during
his tenure= all kids born during his tenure will be
paternal half siblings
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Cooperation via Reciprocal Altruism
• Individuals take turns giving and receiving benefits
• Reciprocal altruism requires1. Frequent opportunities to interact2. Keep track of help given and received by specific
individuals3. Stop helping if don’t receive help in return
Don’t get cheated!! Primates likely to meet requirements
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Monkeys and apes have big & complex brains, particularly neocortex – why?
galago
rhesus
chimpanzee
- Cooperation- Learning- Complex behavior- Problem solving
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Learning and problem solving evolved for ecological reasons: Ecological Intelligence Hypothesis
Solving complex ecological problems• Processing inaccessible food items
• Extractive Foraging• Locating and remembering food sources• Navigating between food sources
• Cognitive Maps
• Apes, Capuchins larger brains, more complex foraging
• Many simple species make cognitive maps, navigate complex food sources• Butterflies, birds, Aye Ayes
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Learning and problem solving evolved for social reasons: Social Intelligence Hypothesis
• Solving complex social problems• Keeping track of kin• Keeping track of relative rank• Remembering benefits given & received• Manipulating rivals• Managing coalitions
All the joys of living in a large group!
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How do we define culture in humans?
• Learned• Patterned
• Nonrandom• Inter-related
• Systematic• Transmittable
• Learned• Stored• Accumulates
• Are humans unique?
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How do we define culture (protoculture?) among nonhuman primates?
• Information acquired via social learning
• Not a species typical behavior• Not genetically inherited• Presence/absence not only due to
ecology• Different patterns of behavior in
different groups
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Culture, Behavioral Traditions, Protoculture
• Potato washing in Japanese macaques
• Chimps:• Ant fishing• nut cracking• Hand-clasp groom
• Still, a large difference from humans• Single behaviors• Limited domains• Little accumulation