MaleMale Competition

1
Lecture 15

• Male-Male Competition

2
Sexual dimorphism and Male PI

• Female grouping patterns affect male pi
  clustering of females makes them economically
  defensible solitary females favor monogamy, low
  dimorphism and high male PI
• Confidence of Paternity increases male PI
  external fertilization increases CP
• Complementarity increases male PI, conflicts
  between feeding and caring for infants generates
  complementarity, when the payoffs to female PI
  increase with male PI. Most important for humans.

3
How do Men Get Mates?

• Harder for a man to get mates than it is for a
  woman. Basic asymmetry means that males have to
  compete for women.
• Why?
• Because women are the limiting good for male
  reproductive success. Women can always get
  pregnant (can find a willing partner), men cant
  always get a sex partner.

4
Remember Components of Sexual Selection

• Female choice men with more to offer (1. good
  genes, 2. protection, 3. investment in offspring)
  get chosen more often by women than men with less
  to offer
• Male/male competition Some men may be able to
  keep other men from mating

5
How Do Men Overcome These Barriers?

• Bride service Common practice in small scale
  societies where resources cannot be accumulated.
  Men come and hunt or work for their
  parents-in-law sometime for years.
• Bride wealth Wealth can be accumulated, men and
  their families make major gifts to the families
  of brides, substitutes for labor. Herding
  societies, Africa cattle. Lamalera example

6
(No Transcript)
7
How Do Men Overcome These Barriers? (contd.)

• Bride capture What if a man comes from a family
  with few resources? His third option is to
  capture a wife from another group of males.
  Sporadic raids, typical of tribal warfare. The
  spoils of tribal warfare are often ponies, cattle
  (to be used for bride wealth) or women
  themselves. These women may be the first wives
  of young men, or later wives of men who managed
  to pay bride wealth for a first wife.

8
How Do Men Overcome These Barriers? (contd.)

• Resource Accumulation As the concentration and
  ability to accumulate resources increased in
  human history, another route to gain wives was
  created. Control resources that women and their
  parents want for a reproductive resource base.
  Then the families of women will compete with each
  other to get their daughters married to you (i.e.
  through dowry).

9
The Male Supremacist Complex in Tribal Societies

• Bride wealth and bride capture
• creates endemic raiding
• puts high value on warriorship, well-being of
  group depends on male fierceness, nice guys dont
  cut it
• male/male bonding and preparedness for raids,
  often mens hut, men may not sleep with wives,
  part of life course when young men live in
  barracks

10
Video of Male/Male Competition for Female Choice

• Leking
• Males come together from a dispersed population
  and perform before females.
• See three examples
• Nubian wrist knives, intervillage club fights
• Disregard inbreeding issues raised by speaker,
  low probability of conception, must be more to
  story in terms of female choice
• Kachepo stick fighting (horticulturalists)
• Club fights very common in tropical South America
  Ache before modern period

11
Video of Male/Male Competition for Female Choice
(contd.)

• Wodaabe (pastoralists) male beauty contests,
  seems very funny from our point of view. But
  what are they displaying?
• Teeth and whites of eyes two very good bioassays
  of vigor, good genes.
• Symmetrical white teeth testify to healthy,
  uncompromised development (move stars know this)
  and whites of eyes testify to current health
  (jaundice, malaria)

12
(No Transcript)
13
(No Transcript)
14
(No Transcript)
15
Logic of Same Sex Conflict

• This leads us to the concept of effective
  polygyny which can be understood in terms of the
  relative reproductive variance of the two sexes.
  The sex with the greater variance will compete
  for access to the sex with the lesser variance.

16
Polygyny Can Take Various Forms

• Harem defense polygyny Males fight to
  out-compete other males and dominate a harem of
  females. Requires that
• Females are grouped in space
• Females do not gain very much from choosing a
  particular male. One harem leader is as good as
  another.
• Examples are Deer and many other ungulate
  mammals and some primates. Very powerful men in
  highly stratified societies (Moulay Ismael the
  Blood Thirsty).
• This type of polygyny usually leads to different
  life histories for males and females, with males
  senescing more rapidly than females. Males
  maturing late and engaging in more high risk
  behaviors.

17
Resource Defense Polygyny

• Resource Defense Polygyny (female choice) Males
  compete to acquire resources such as feeding
  territories and females distribute themselves in
  male territories according to polygyny threshold
  model tends to produce lower levels of effective
  polygyny than above

18
Good Genes

• Males have good genes Female choice where
  females choose males for genetic quality and
  males vary in markers of quality.
• Where females invest less than males, such as in
  the polyandrous spotted sandpiper, and females
  have higher reproductive variance and fight more
  spectacularly