Lecture 15 Male-Male Competition
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.
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 can’t always get a sex partner.
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
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
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.
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).
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 don’t cut it… • male/male bonding and preparedness for raids, often men’s hut, men may not sleep with wives, part of life course when young men live in barracks
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
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)
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.
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.
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
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