Sociobiology and Socioecology
Blue: Lab notes
Wednesday, February 13, 2013
• Sociobiology: Describes the effects of male/female differences in reproductive
biology on social behavior. Biological bases for social behavior.
o Kin Selection: Hamilton's Rule: Family comes first. You are more willing to
help family members other than strangers.
o Males and Females: different minimum investment to ensure offspring
o Everything stemming from the asymmetry in required parental investment
by males and females.
o Naturalistic Fallacy: If X happens in nature, we should do it too.
o Males Mammals: more promiscuous
o Female Mammals: More choosy
One result: Male competition for access to females
• Q: Aren't there instances in which females reap a benefit from mating with
more than one male?
o To prevent infanticide
• Female mates with multiple males
• Males provide infant care
• Still related to reproductive biology (twinning)
• Female choosiness is an old idea:
o C. Darwin: "The female, with the rarest exceptions is less eager than the
male… she is copy and my often be seen endeavoring for a long time to escape."
o Formalized as "Bateman's Principle
• Angus Bateman: Fruit flies
• Provided empirical support for the notion that promiscuity is a
• This is usually true in mammals… but it's a generalization.
• Another example:
Primate females that mate with multiple males partly as a
strategy to avoid infanticide
• Investment in Reproduction
o Not sex per se.
o Flicker (Colaptes auratus) [woodpeckers]
• Male: Hammers out nest
• Male also does lion's share of incubating and chick guarding
(grater parental investment) so…
• Females compete for access to males
Some females maintain two nests with two male mating partners.
Most birds pair-living
• Q: Do principle of sociobiology apply to human behavior?
o E.g. Does Bateman's Rule apply to humans? • A while different course.
• Humans more than any other animal rely on LEARNED patterns
of behavior in day-to-day life.
Culture modifies and constrains biologically- mediated
• SO: Permanent male/female association in primates may be partly
the result of females attempting to avoid male harassment and infanticide
• Q: Why be social at all?
o True sociality (established relationship and individual recognition) among
mammals is rare.
o Many mammals solitary or form aggregates
• Social Mammals:
o Some carnivores
o Spotted Hyenas
o Lions and big cats
• For some, benefits are obvious
o Cooperative hunting
o Cooperative infant care
• Q: Why do primates live in groups?
o They are definitely costs for group-living…
o Costs of sociality:
Competition of food
• Competition of mates
• Enhanced disease transmission
• More conspicuous predators
• Predation Defense Model
o Carel Van Schaik
Primates live in groups to protect themselves from predators
o More eyes and ears
o Physical Defense
o Dilution effect (probabilities)
• Resource Defense Model
o Richard Wrangham
o Primates live in groups to have better access to food
o Large groups can displace small groups at clumped resources like food
o Solitary: no within group competition for food
o But, it may be to your benefit to put up with some within group
competition in order to win between group contests
o Also: Shared knowledge of where to find food resources
o May contribute to foraging efficiency
• There is good empirical support for both models
o Group size often seems to be determined by balancing costs with the
• So: Many primates are social • How primatologists classify social groups:
o Female bonded groups
• Many primate species live in female-bonded kin groups that
remain stable over time
• Females stay in their natal (birth) group their entire lives, so that
females live with their relatives
• Female Philopatry
• Philopatry: literally "love of the father land"
• Remain in natal group as an adult
• In primates, one or both sexes disperses before reaching sexual
maturity (Exception: callitrichids)
• Key: Inbreeding Avoidance (Avoiding inbreeding depression)
• So, in female-bonded primate groups, females
o Male bonded groups
• Fewer primate species live in male-bonded kin groups
• Males stay in their natal (birth) group their entire lives, so that
males live with their relatives
• Male Philopatry
• Female Dispersal
• Q: Why are male bonded groups rare?
Males compete more for mates.
Females compete for access to food ----> males compete
for access to females
Food can be shared among several females, but most
female primates can only be impregnated by one male.
Attempts by individual males to monopolize access to
females may prevent formation of male alliances.
• Remember: competition between males for access to females can
be very intense, and may even result in death.
See box 5.2 on pp 129-130 for more classification schemes.
• Social Structure: describes how many adults of each sex are in
social groups. Ratio of adult males and females within a social group
Solitary: individuals live alone (Aye-aye, orangutan, mouse
Offspring can only live with mother until weaning
M & F only come together to mate
Many nocturnal primate species previous thought to
be solitary actually live in dispersed social networks:
• Individuals sleep in groups and have
• Forage alone ("solitary foragers")
Family: 1 male, 1 female, dependent off spring (Gibbons,
Indri, titi monkey)
Dispersed: forage separately, sleep together
Cohesive: feeding, traveling, resting together
Single male/Multi female: (Langur, Gorillas)
1 adult male, 2 or more adult females
Unattached males solitary or form all male bachelor
More in danger for infanticide Multi male/Multi-female (Chimps, Spider monkeys, howler
Multiple adults of each sex in social group
Baboons, maccas, bonobos,