Human behavioural ecology

1. Human behavioural ecology 2009/11/27 張伊鈞

2. Human behavioural ecology • Introduction • Studies of foraging • Studies of reproduction • Overview

3. 3.1 Introduction • Aim • Determine ecological and social factors affect behavioral variability within or between populations • Models and assumptions • Cultural traits were equated with genes.

4. 3.2 Studies of foraging • Resource choice • Foraging group size • Food sharing • Traditional conservationists or a Tragedy of the Commons?

5. Resource choice • Optimal diet breadth • Nutritional demands • Risk

6. Optimal diet breadth • Maximize caloric returns • Cost-benefit considerations • Encounter rate vs. food ranked e.g. Alyawara--- seeds vs. flour • Tool availability, other forager informations, seasonal variations…

7. Nutritional demands • Vegetable and meat • Hunting is dangerous. Why do men do it? • The effects of macronutrients on physiology, growth and fitness are still entailed in testing the importance on diet choice.

8. Risk • Risk reduction vs. forager’s interest • Ache men: risk-prone strategies

9. Foraging group size • The conflict between joiners and members: • Rn-1 >Rn >R1 ( R= the per capita return rate)

10. Food sharing • Food storage is unfeasible… • Kin selection • Tit-for-tat reciprocal food sharing strategy • “tolerate theft”

11. Traditional conservationists or a Tragedy of the Commons? • Short-term cost for long-term benefits? • Hunting rate vs. game density • Time allocate to hunting • Amazonian: short-term maximizing strategies. • Long-term conservationist strategies: territorial & “punish cheatrers”

12. 3.3 Studies of reproduction • Sex differences • Mating system • Kin selection • Parental investment • Reproductive strategy and social change

13. Sex differences • Sexual dimorphism in size • Sex differences in behaviour • Provision of parental care

14. Sexual dimorphism in size In human, are the levels of dimorphism in stature higher in polygynous than monogamous societies? No evidence supported!! • Marriage practices bear little relations to mating behavior and competition • The current marriage system are too short time for natural selection to change gene frequencies. Wolfe’s (1980): Nutritional differences contribute to dimorphism differentials between populations. • Different kinds of polygyny will favor different competitive male traits. (e.g. 地位. 抱負…)

15. Sex differences in behavior • E.g. violence, intersexual behavior, and mate preferences • But may be oversimplification and have little progress of inter and intra-cultural variability in sex differences.

16. Provision of parental care The risks by a single parent : • How safe is the environment? • What is the level of nutritional stress? • Are alternative caretakers either available or suitable?

17. Mating system • Resource-defence polygyny • Monogamy • Polyandry • Female choice and the polygyny threshold model

18. Resource-defence polygyny • Male compete for power or resources in order to attract females. • resources be monopolizable • Chagnon(1979) acquire resources easily • Dickemann(1979) extreme environment instability

19. Monogamy • Hunter-gatherers • Complex combination of historical, ecclesiastical and sociopolitical considerations • Reproductively advantageous to limit heirs

20. Polyandry • Most arrangements are fraternal. • The family estate will not be fragmented among multiple heris. • High labor demands required. • Different marital arrangements can occur within any one society.

21. Female choice and the polygyny threshold model • Female choiceenhance reproductive success. • polygyny threshold model: • Women’s labor contributions vs. the level of polygyny • This may indicated that polygyny can be favoured by women

22. Kin selection • Relatedness to sets of dependent offspring • Manipulation of kinship terminology

23. Relatedness to sets of dependent offspring • Full sib group (individuals with high reproductive value) 0.025 0.3138

24. Manipulation of kinship terminology • Yanomamo: utilize a kin classification system • Male strategy avoiding investment • low paternity • matrilineal inheritance

25. Parental investment • Targets of investment • Measurement of parental investment • Parental investment and demographic transition

26. Targets of investment • Evolutionarily based predictions are supported to neglect or kill the low reproductive value of the offspring. • Parents provide better care for sons than daugthers. • The effect of competition and cooperation among sibs and their parents.

27. Measurement of parental investment • Breast milk, food provisioning, education, inherited resources and status… • Parental resources and offspring fitness were positively correlated.

28. Parental investment and demographic transition • Decline in marital fertilty. • Production of more competitive offspring (e.g. by education & training)

29. http://pic.pimg.tw/kunlinjohnlee/498a3e93aff59.jpg Reproductive strategy and social change • Mukogodo vs. Samburu • Bridewealth • Relocation • Intermarriage • Reproductive strategy appears to have driven a major subsistence shift.

30. 3.4 Overview • Critiques and limitations • Cultural complexity • Cultural evolution • The study of humans in changing environments