EBH 200: The Evolution of Human Behavior

modules 1-3

behavioral ecology

How differences in behavior affect the likely hood that an individual will survive and reproduce

Charles darwin

came from a well-to-do family, studied the distribution of organisms throughout time, and developed the mechanism for evolution: natural selection

natural selection

the process whereby organisms better adapted to their environment have a higher probability of survival and produce relatively more offspring

3 conditions essential for evolution

variation, struggle for existence, and heritability

variation

Before selection, members of a species exhibit differences in morphological, physiological, and behavioral characteristics

struggle for existence

After selection, some individuals have a higher probability of surviving than others, owing to their distinctive characteristics

heritability

final population; parents pass on some of their distinctive characteristics to their offspring

example of natural selection

camouflage of desert mice color on dark rocks; more dark mice to survive and reproduce

evolutionary fitness

the measure of relative reproductive success, incorporating an individual’s survivorship and his/her offsprings survivorship

benefits of group living

protection against predators, infanticide avoidance, thermoregulation, defense of resources, foraging efficiency, opportunities for cooperative infant care

costs of group living

must coordinate movement, harassment from group members, disease and parasites, competition for resources, and cover greater travel distances to meet energetic requirements

social organization

the size, sexual composition, and spatiotemporal cohesion of a social group

all social groups include

dependent offspring

spatiotemporal cohesion

how likely a group is to stick together

dependent offspring

infants (unweaned) and juveniles (weaned but not yet reached sexual maturity)

socioecological hypothesis

predicts relationship between resource distribution and social organization

sex differences in settlement decisions

female fitness and male fitness are limited by different factors

Bateman’s principle

Females are limited by the number of eggs they can produce, and males are limited by the number of females they can seduce

Female distributions follow the distribution of…

food

Male distributions follow the distribution of…

females

fission fusion societies

high degree of fluidity in group membership across space and time, and relate to human behavior and interactions

group size in hunter-gather societies

Environmental variability often forces hunter-gatherers to live in small, mobile groups ranging in size from 35 to 80 individuals; membership can be fluid but membership is not chosen at random

social-brain hypothesis

explains why primates, humans, have such large brains compared to other species, they live in complex societies that require advanced cognitive functions, and bigger neocortexes

Dunbar’s number

suggested cognitive limit to the number of people with whom one can maintain a stable, social relationship

Human group size

50

criticisms of the social brain hypothesis

even if other species have the same social organization of apes, apes still have a higher neocortex ratio; orangutans move around on their own but are still intelligent

How is sexual reproduction costly?

time and energy expenditure, predator and disease exposure, competition, only half the genome is passed on

advantage of sexual reproduction

There is a recombination of genetic material, which creates a diversity that didn’t exist in the parent generation

3 Hypotheses that highlight the importance of genetic diversity

the lottery hypothesis, the red queen hypothesis, and the DNA repair hypothesis

Lottery hypothesis

sexual reproduction produces variable offspring that will thrive as environments change over time

example of the lottery hypothesis

aphid reproduction is sexual in an unstable environment and asexual in a stable environment

The red queens hypothesis

sexual reproduction enables organisms to remain competitive in an evolutionary “arms race”

example of the red queens hypothesis

predator-prey, both evolve

DNA repair hypothesis

Damaged DNA has deleterious consequences. With asexual reproduction, all mutations are passed on, but with sexual reproduction, crossing over repairs the DNA, and the heterozygous state can mask mutations

anisogamy

sexual reproduction involving the union or fusion of two dissimilar gametes differing in size or form

example of anisogamy

human sperm and eggs

isogamy

games of equal size and or form

why are there two sexes?

so each can excel in something specific

mating game

addresses how differences in parental investment shape reproductive behavior

mating game results

Female sexiness doesn’t impact successful mating, but male sexiness does. Females are more selective, but it takes them longer to have children, all females find mates, and all males do not

parental investment

time, energy, and resources that a parent invests in a rearing offspring

reproductive rate

number of offspring produced over a breeding season, year, or lifetime

sexual activity

investment in activities related to mating, whether mating itself, competing with others for mates, choosing mates, etc.

operational sex ratio

ratio of the number of reproductively active adults in the population

not reproductively active

sex doesn’t lead to conception like when pregnant or lactating

Males

Which species has low parental investment, high potential reproductive rate, high sexual activity, and competes for mates?

Females

Which species has a high parental investment, low reproductive activity, low sexual activity, and chooses mates?

meerkats

reproductive skew in both directions, one male and one female so only one of each have a lot of mating

Monogamy

one of each sex

Polygamy

plurality on at least one side

Polyandry

one female, many males

Polygyny

One male, multiple females

polygynandry

plurality of both sexs

serial mongamy

each sex has multiple exclusive partners

relative canine size

Canine size is the same for both sexes in monogamous species, but greater in polygynous and polygynandrous species due to competition for mates

testes size

largest for polygynandrous species because females are also mating with multiple males, and males with larger testes will be more successful

where does polygyny exist?

where life is easy and women are self-sufficient

Where does polyandry exist?

where survival is tough and resources are limited

Mating system in Africa and Why?

they are polygynous because women are self sufficient so the men have time and resources to care for many women

Mating system in Inuit society and why?

monogamous because men cant support or hunt for many women and women are not self sufficient

Tibetan mating system and why?

polyandry because of extremely difficult living conditions

What are some monogamous behaviors?

no male competition, more female competition, female choice, more paternal or equal investment, fewer sex differences socially

Mating vs marriage

mating is a biological concept where marriage is a social construct

functions of marriage

assigned parental responsibility, social regulation of sexual competition, assignment to social status, formation of alliances, and exchanges

bride-weath

payment that a man or his family makes to a woman’s family

Bride-service

form of bride-wealth where a man works for his future wives family for a period of time

Dowry

payment that a woman, or a woman’s family makes to the man or man’s family

reciprocal exchange

the roughly equal exchange of gifts between the woman’s and man’s families

Why bride-wealth vs. dowry?

it depends on the scarcity of each sex

High male reproductive skew with polygamy…

there are less women available so men pay dowry for the loss of daughters at home

Monogamy with low male reproductive skew

less men available so dowry is paid

What determines bride-wealth value?

early puberty, bigger women with more fertility or nutrition

cousin marriages

less genetic diversity but keeps wealth in the family and is seen more frequently in rich royals like king tut

What are the additional protections against incest?

single sex dispersal and an innate inversion to inbreeding

arranged marriage

marriages in which the selection of the spouse is outside the control of the bride and groom

Special observation from taiwanese minor marriages

the children arranged to be married at a young age grow up as brother and sister, so they end up finding each other unattractive

Hopi women

divorce easy

divorce rates in nepali nyinba

marriages involving 3+ husbands are more likely to leave or become “partitioned households”, younger men are more likely to leave

conjoint household

has a second wife

partitioned household

the male leaves

7 year itch

after children mature at age 7, divorce rates go up

bower birds

makes shrines, defends against other males, females like males who build attractive bowers

sexual selection

special application of natural selection associated with mating success

intrasexual competition

individuals of one sex compete with other same-sex individuals for access to mating partners

Intersexual choice

individuals of one sex choose among opposite-sex individuals for their mating partner

Fibonacci’s sequence

next number is the sum of the previous numbers

Golden ratio

1: 1.618 aka perfection

symmetry means…

developmental stability

handicap principle

signals -particularly those related to sexual reproduction- are honest, reliable indicators of an individual’s health and condition; individuals in poor health and poor condition cannot afford to produce extravagant signals

examples of male mating choice

ovulating females, 0.7 waist-to-hip ratio

example of female mating choice

high testosterone induced features, Dorito shaped bodies

Male choice

short term, kindness, intelligence, fidelity, fertility

Female choice

social status, ambition, dominance, intelligence, kindness, and good health to secure resources

Chastity

no sex before marriage; had variation in rankings between cultures

status

defined differently by different cultures, but linked to male fitness and leads to more offspring

Esther hongs photoshop project

showed that beauty standards differ

symmetry preference is

adaptive to ecological conditions like mortality rates

the hazdas

male hunters preferred symmetry in females, and pregnant nursing women valued symmetry in males

frequency dependent mate selection

rare phenotypes vs common ones

what are the parts of competition for mates

1. straight competition

2. competitor derogation

3. self-promotion

4. competitor manipulation

5. mate manipulation