LIFE IN SOCIAL SYSTEM COMPOSED OF
MATRIFOCAL, RANKED LINEAGES: Slides of
Vervet monkeys
Introduction
to Life history tradeoffs and sex differences
1. Gamete size and parental investment
2. Sex that invests less is in short supply
3. Creates following pattern:
a.
Less investing sex
1) more mating competition;
2) less choosy
3) fitness a function of access to
mates
b) more investing sex
1) choosy
2) fitness a function of resources for
PI
As
in most mammals, female primates do not expect provisioning from males. One result of this is that the paternity
confidence issue gets translated into female promiscuity (because males are
more tolerant of and perhaps may even be protective of infants that they might
have fathered). This may include low
paternity confidence like 20% because provisioning isn’t an issue.
Larger context of lecture -How life
histories play out in a particular context. This example concerns both males
and females. One society that
individuals grow up in. Even among our
nonhuman relatives, individuals have to deal with social restrictions on access
to resources that result from social stratification. One of the big costs of life in social groups is that you have to
compete with members of that social group for access to resources. Particularly if the resources are
monopolizable (don’t compete over leaves, do compete over fruits).
Vervet Monkeys: Cercopithecus aethiops
Species very
successful. Widely distributed across
Africa and from the Sahara to South Africa without speciating.
Sexual dimorphism moderate cf. baboons,
females 10 lb., males 15. Baboons males 2X
Small
semiterrestrial, feed and spend much time on the ground as do baboons but must
be within a sprint of trees. Savannah
woodland species but too small to defend selves. Baboons 40-60 lb., serious dentition, can afford to walk out into
the savannah away from the safety of trees.
Birth:
bond between mother and infant is an essential building block of primate
sociality. Strong attachment then
continues throughout life.
2. Frank day
7,
vervet’s have a characteristic 6 point attachment, arms, legs, mouth (2 nipples
at once) and tail wrap. Responsibility
for maintaining mother infant contact is the infant. Infant much be born both physically coordinated and
psychologically motivated to cling.
Otherwise removed from the gene pool.
3. Finger,
Frank and
Plain (Frank’s olde weaned brother) Day 7 - first widening of social
network based on the relationship between weaned but not yet independent
juvenile and newborn. This relationship
is one based on uterine kinship.
All individuals which came from the same uterus have a lifetime
attachment to each other based on their primary attachment to their
mother. Paternity less readily
identified even though genetic relationship can be identical, half sib through
father. Therefore,in these monkey
groups kin recognition is based on basic attachment to mother which forms a
mesh between maternal relatives. These relations are significant in adult
life. The newborn male, when he reaches
puberty will probably migrate to the neighboring group that his older brother
moved to a year or so before. He can
expect social support from his brother.
4. Whisker eats
sap,
Willy at 62 days. Why is offspring
responsible for clinging? Because of essential conflict between provisioning and
care for young which is central to the life history of all female primates
including humans. It is difficult to
forage efficiently and have to hold an infant at the same time. Female monkeys have to feed, flee from
predators, climb to dangerous heights.
Infant cannot encumber her arms and legs.
Same is true for
human women but not based on the infant’s ability to cling. Carrying sling a key factor in the evolution
of the human brain. A tool to carry an
infant with a large underdeveloped brain.
5. Frank visits
his
brother Plain (14 days) - first movement away from his mother’s body to his
close kin.
A key
behavioral unit among primates is the embrace
2 significant
characteristics:
It is based on the mother/infant attachment
and carrying/lactation. So it is used
to signify that relationship. “we are
as mother and child to each other”
There is a
physiological response to the embrace which leads to calming distress and
pain. Think of a distressed individual
turned the other way around. Not the
same physiological response.
6. The embrace
used
as a greeting, 2 adult female langurs in Ceylon, when we see primates embrace we have a strong indicator that they
are related as uterine kin
8. 3 males
(relatives) baboons. Mutual embrace
to cement a social agreement, a coalition in the face of a threatening male
(unrelated). “remember what we are to
each other”
9. Wounded
Vietnamese
soldier, the embrace eases pain.
Giving child shots, lower pain threshold when being held facing away
from parent’s body than facing.
10. Emotional distress, Wichita Falls tornado,
1979
This
relationship between mother and infant is the fundamental and primordial
building block of primate sociality. It
ramifies into more elaborate networks than the simple dyad. It forms
(as the uterine link or the MATRIFOCAL bond) kinship relations that are
based on maternity. This kin link
precedes language and is based on familiar association. Matrifocal kin are recognized by virtue of
their association with the same female.
We nursed from the same nipple, my mother and your mother nursed from
the same nipple.
In many monkey
societies, this matrifocal association becomes the basis of continuity
in social groups. A monkey troop’s
solidary core, comes from related females and their descendants. Since females rarely migrate from their
natal group, their kinship network links generations and provides continuity
through time. Matrifocal association
does not necessarily create matriarchies, nor must it be traced only through
females. In chimpanzees, daughters
migrate and sons stay in natal group.
The continuity of the community stills rests on the principal of
matrifocality through males, sons, brothers, uncles and male cousins.
11. Pink grooms
Moue
while Line, her male peer nurses.
Pink is the daughter of the top ranking female and sister of #2 in a
group of 17 adult females, Moue is middle ranking. As a young weanling she is establishing her social relationships
for life, entering the hierarchy of adult females. She is socially fearless since her status is guaranteed by her
entire maternal lineage.
Why? Vervet monkeys feed on resources which are
rich and can be monopolized. Therefore
group members are competitors for food items.
Mothers see to it that daughters have the same social prerogatives as
they do. They are alert to having their
offspring disrespected. Offspring take
status on the basis of birth order, among females these rankings endure
throughout adult life. Elder sister,
younger sister. Each offspring of elder
sister automatically ranks above the offspring of younger sister, etc. System creates “Ranked matrilines or
matriarchies” whose rankings only
change if drastic changes such as all adult females in the line die of a
disease, juveniles will lose status. Notice the importance of female-female
competition for status.
The “rich get richer”. Privileged status gives access to resources which help maintain
privileged status. Only females with
low status migrate and take lineage with them (female Moses phenomenon).
12. Yearling
male
baboon initiates harassment of an adult male baboon, yearling has relatives
in the group, adult male does not.
Youngsters learn rapidly who they can dominate and who they can’t based
on the status of their matriline.
13. Ranked
matrilines have common interests and use grooming to cement it. Two top females in hierarchy groom female who
is bottom ranked 17th, after she broke her leg.
14. Matrilineal coalition of 3 juvenile females vs.
an
adult female of lower rank.
Common
interests among matrilines
are based on feeding rights in group’s territory, females strongly
committed to territorial defense, as are their juveniles. Even leaf eating monkeys are highly
territorial, have matrifocal social groups, but not ranked matrilines. Why?
Keeping exclusive rights to a feeding territory pays off but fighting
over which leaf to eat doesn’t.
Most dominant males in groups often act like
gladiators, but females maintain the margins with swift defense.
Adult males are “strangers” in most monkey
societies. They join the group through migration sometime after puberty and
some males will migrate a number of times.
Often entrance into a group is mediated by female sponsorship. Stranger males join the group by making
friends with particular females, often ones who are low in status and don’t get
enough attention from resident males.
Males will hang around with them until most group members are used to
them and females aren’t soliciting group males to attack them. Then they will slowly work out their status
in the male hierarchy. Reported for
both baboons and vervets.
In vervets male
migration studied by Seyfarth and Cheney.
Found that males always improve their mating status when they move. Get more favorable sex ratio, more females
in estrus, females willing to be friendly with them, more coalition partners
(older brothers). Males have choices,
suggests that they study situation from afar before making their move. Very strong likelihood of moving where there
is a male cousin or brother already established. A ready coalition partner based on a matrifocal (uterine) kinship
link.
15. Big, the perfect male monkey, early middle
age,
healthy, muscular, virile, good with kids, protective of females and young,
careful to maintain his support network with other males in the grou. Females support preferred males in status
competition and high status males also have higher rates of paternity.
Red, white and
blue display, dominant males walk
around with their tails in the air, giving full view to their genitals,
casually show it to other males. In
vervets color intensity of blue scrotum actually a bioassay of testosterone
levels. Fades to pale after losing a
major contest.
16. Dominant
male
plays leader role when travel is dangerous, not otherwise. Vervet females move along feeding on their
own until get to dangerous swamp crossing point, wait at edge until dominant
male, Big, and an elderly male show up.
Elderly male may have been previous top male, now thin and arthritic but
Big defers to him, play wrestles with him in highly ritualized way, grooms him
(aged older brother perhaps?).
17. 2 top
males,
vigilant, No 1 can count on No 2 to back him up.
18. Big hears
neighboring
group, dashes to top of tree to locate them.
19. 5 adult
males
crowding a large owl (large owl in
upper right) all other lumps are adult males sitting in strategic points in the
canopy). The males gradually narrowed
distance between them and owl until it flew away. Females and young were feeding on the ground below the tree when
the alarm was called. Males raced up to
this position.
20. Big, highly
popular, spends relaxed time sitting with others, females and all male
juvenile group
21. Big baby
sits,
7 infants have been left under his protection while their mothers feed. Vervet mothers stop carrying at 3 months
because of feeding interference from large infants. Continue lactation for a year.
Often use dominant male to baby sit.
22. Big groomed
by
other males. Male/male grooming
very common in vervets.
23. Adult males
may
present for grooming but be ignored.
Adult females about 2/3 size of fully grown males. Status much higher than in baboons where
males are twice as big.
Hardy presents
to adult female in top matriline
24. She ignores
him
25. He falls
asleep
waiting and she leaves
27. Male/male
play
wrestling, very prominent in this species, controlled and ritualized when
between adult males. Here the #2 plays
with #5. Big plays with juvenile and
subadult males with great abandon.
28. 5 juveniles
and
infants play together during rest period
29. 2 matched
pairs
of male players
Ranked
matrilines and status by sex
Male and female
status hierarchies largely separate matters, rarely direct conflict between the
two.
30. Feeding
tests. Last week of study I provided unusually
good, concentrated food packages, not enough for all to feed together. Dominant male feeds with a matriline (4th
ranking), mother and her two sons
31. Big
threatens off
the approach of a lower ranking adult male. Uses eye lid threat, exaggerated stare, intention movement, in
primates direct, unwavering gaze implies contemplated direct action. A dropped gaze implies lack to motivation to
have an altercation. Subordinates often
exaggerated staring in other directions.
32. Big
feeding when
daughters of #1 and #2 females arrive.
They are juvenile cousins. Big
threatens them off.
33. The eldest
of the
two juveniles returns his threat.
The two juveniles subsequently move in and sit down to eat beside him.
Male
coalitions
34. New male
with a
serious wound in throat from a canine slash. May never be accepted in the group even though he could dominate
Big if he could get him one on one.
Most of the time he met a solid opposition of males against him,
especially Big and his #2.
35. Subordinate
males
readily form a coalition against stranger male. Females didn’t like him
either and gave alarm calls whenever he was near their infants. Why?
He had no confidence in paternity since he wasn’t in the group when the
infants were conceived.
36. Female/female
coalitions, an ever present danger for males. Here 4 adult females in a coalition against Big who is running
flat out for a tree which he will climb, turn and face them. Big had accidentally made an infant squeal
by walking up behind him and provoking a startle response. Hell hath no fury like a matriline of
avenging mothers. This related to both
female coalitions and degree of sexual dimorphism (cf. baboons), which among
other things is a function of body size.
Take home
messages:
1) In this particular context, we have very
different life histories for males and females, based on fact that males
migrate at puberty and females remain in natal group with lifelong
relationships of cooperation of matrilineal kin.
2) Since males
in these populations have to compete with other males in new social systems,
they have to invest in extra growth (hence sexual dimorphism); females face a
different tradeoff and invest that energy in reproduction.
3) Females, once
they have reached adult stature (2/3 that of males), go directly into
reproduction. No sub-adult period in
females, but there is in males. Males
continue to grow and learn competitive skills.
Sub-adult period can last 2-3 years for male monkeys depending on
species.
4) No pause for
fat storage for females as for humans females as we will find in next
lecture. Female monkeys complete growth
in body size and commence reproduction.
5) Timing of
migration for males and locus of migration for males is very specific to each
individual male’s life history. E.g.
Seyfarth and Cheney found that sons of high status mothers delay migration and
even mate with females in natal group.
Because it is better and easier to get that growth in within a group in
which you have high status. Why,
because Mom sees to it that you have priority of access to high quality,
monopolizable foods. The group a male
migrates into has been demonstrated to have favorable sex ratio and potential
allies (relatives). Males who have
attained high status and have been able to keep it for 5-6 years often leave
once their daughters start reproducing.
