Behavioral Ecology Of Parental Investment Strategy Of Tibetan In The Eastern Tibetan Plateau

How human beings choose different survival and investment strategies in different ecological environments and how they balance the benefits and costs of parental investment is a key focus of human behavioral ecologists.Natural selection tends to optimize energy and time over the life course;since the resources possessed by individuals are limited,parents will face the dilemma of how to balance resources allocation.For example,how do parents weigh the quantity and quality of offspring?How do parents trade-off age at first birth and age at last birth? How much effort should be put into offspring of different sexes to achieve maximum fitness? In recent years,scholars have mainly studied the Tibetan by means of cultural anthropological participatory investigation and ethnographic description based on normative practice,and few studies have used quantitative behavioral ecology or on-the-spot demographic data to conduct empirical investigation of individual variation in behavior.This work is based on behavioral ecology,by providing quantitative data of Tibetan population in eastern Tibetan plateau,focus on how reproductive fitness shapes the preferences of parental investment,how siblings compete for limited parental resources to maximize fitness and how parental reproductive strategies adapt to specific cultures and environments.Zhuoni County belongs to Amdo Tibetan,one of the three major Tibetan areas on the eastern Tibetan plateau,with limited natural resources,but at the same time is remote.The Amdo Tibetans,who have lived here for generations,have a unique way of life,which included sending a large number of boys to monasteries to live as celibate monks.Most Tibetans maintain the traditional agro-pastoral life,while inevitably being influenced by Han culture and modern lifestyle.A series of economic and social ecological changes are affecting their survival,reproductive strategies and development.Therefore,this place is a very meaningful area for the study of human behavioral ecology.Our field work was in Wanmao Township,Zhuoni County,Gannan Tibetan Autonomous Prefecture,Gansu Province for two years(2016-2018).We collected census data,socioeconomic data and reproductive data from 21 villages,530 households,and a total of 3,592 people.Firstly,I used survival analysis and mixed Cox effect model to analyze the different feeding duration and interbirth interval of children,to measure which gender of offspring received more parental investment.Secondly,I address the evolutionary puzzle of why parents would submit a son to a celibate life.The generalized linear mixed model is used to analyze whether male inheritance pattern and fertility rate are related to having monk brothers.Finally,using the event history analysis and taking the age at last birth of women as an indicator,I observe how they change their reproductive strategies with the factors of reproductive policy,geographical location,family helpers and so on.Our important findings are as follows:(1)Boys get more investment from their parents in this area.The feeding time of boys was longer than that of girls under breast-feeding,bottle feeding and mixed feeding.Parents have longer birth intervals after having boys than girls.(2)Monks effectively relax the pattern of competition for household resources.Having monk brothers affects the way of inheritance.Specifically,parents usually send their second son to monasteries to become monks.These monks do not reproduce or inherit,but the eldest son usually inherits parents’ property and takes over the family.And men with monk brothers are richer and have higher reproductive success than those without.Non-inheritors may also move to their wife’s household or migrate elsewhere.(3)Mothers with female family helpers(mothers-in-law and older daughters)tend to have children more quickly.The age at last birth has been declining in the whole region and was declining significantly before the one-child policy.In addition,older women having their last birth later than younger women,meaning that younger mothers are reaching their last birth age at a faster rate.Based on detailed data collection and analysis,this study provides data support and a valuable theoretical basis for the utility of a human behavioral ecology approach to understanding parental investment in the eastern Tibetan Plateau.