Anthropology 101: Human Biological Evolution

Lecture 7: Primate Reproduction and Protoculture

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

Mammalian females are committed to invest in offspring

• Internal gestation (pregnancy)• Lactation (nursing)

• Maternal investment obligatory• Paternal care optional

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

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

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

Intra-sexual selection in primate males

• Male-male competition favors• Large body size• Large canines (NOT meat)• Mate guarding

Inter-sexual selection in primate males

Inter-sexual selection = Female choice favors

• Flashy colors• Energetic displays• Friendly behavior• Paternal care

mandrill

tamarin

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

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

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

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

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

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

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

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

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

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

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.

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

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

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?

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

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

Monkeys and apes have big & complex brains, particularly neocortex – why?

galago

rhesus

chimpanzee

- Cooperation- Learning- Complex behavior- Problem solving

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

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!

How do we define culture in humans?

• Learned• Patterned

• Nonrandom• Inter-related

• Systematic• Transmittable

• Learned• Stored• Accumulates

• Are humans unique?

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

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