Contemporary trends in low fertility can in part be explained by increasing incentives to invest in offspring’s embodied capital over offspring quantity in environments where education is a salient source of social mobility. However, studies on this subject often rely on homogenous populations, missing out on the opportunity to investigate how this relationship is impacted by structural factors that asymmetrically allocate economic opportunities between members of different groups. Using General Social Survey data from the US, I examine changes in the relationship between number of siblings and college attendance for White and Black respondents throughout the 1900s. Results showed that White individuals from larger families had a lower chance of completing at least four years of college education than individuals from smaller families, while the likelihood for Black individuals was more uniform across family sizes. Though results were not significant for every cohort, racial difference was generally larger in cohorts born in the early 1900s and converged in the later part of the century. These results explain variations in the timing of demographic transitions within subpopulations of a nation and suggest that the benefits of decreasing family size on educational outcomes may be conditional on the specific economic opportunities afforded to a family.

Since the 4th century B.C., there has been great interest in facial signaling in both human and non-human animals (Fridlund 1994). Early naturalists believed that the face was linked to the soul, and facial signals were the product of emotional experience (Bell 1806; Descartes 1649). As a result, most facial signaling studies to date have focused on placing facial muscle movement into discrete categories of emotion (Ekman 1970). Facial signals are assumed to be spontaneously produced and inflexible due to their strong ties to emotion; these signals are contrasted to other forms of non-vocal communication such as manual gestures, which are intentionally and flexibly produced (Pollick and de Waal 2007). In recent years, the idea that facial signals can be categorized based on physical form or corresponding emotion has been contested (Fridlund 1994; Waller et al. 2017). Some studies have even found evidence for goal association in great ape facial signals types such as the ‘play face’, which is considered to be an important gesture property (Cartmill and Byrne 2010). But it is unclear as to whether great ape facial signals are capable of taking on all important gesture properties, and if so, how they compare to manual gestures. The goal of this dissertation project was to examine the physical form and social function of facial signals in our closest living relatives, the chimpanzee (Pan troglodytes). The history of facial signaling inspired two different research questions in this project: (1) can chimpanzee facial signals take on gesture properties, and if so, how do they compare to manual gestures; and (2) is there variation in the physical form of chimpanzee facial signals, and how does this compare to other ape species. To address these two questions, I collected data using a combination of two previously described sampling methods: the focal individual sampling method and the opportunistic sampling method. A comparison of these two methods can be found in Chapter 1. The results of this dissertation suggest that chimpanzee facial signals can be used as gestures (Chapter 2), and that there is extensive variation in the physical form of chimpanzee facial signals when compared to other ape species (such as gibbons; Chapter 3). These findings have important implications for the evolution of sociality, gestural communication, and human language, which is discussed at the end of each chapter.

How do social norms spread in a population? Which processes affect whether a social norm persists over time or disappears quickly? These are the questions that guide this dissertation. In modeling the spread and maintenance of social norms, I employ and integrate two theoretical frameworks: cultural evolution theory, an anthropological framework that aims to model how culture changes over time and space and understands cultural change as somewhat analogous to Darwinian evolution; and sexual conflict theory, a theoretical perspective that investigates how conflicts of interests between the sexes play out over evolutionary time. Descriptive social norms refer to common behaviors or conventions of a group. On the other hand, prescriptive social norms say something about what is morally right and how people should behave. I argue that this distinction is crucial for pinpointing the processes affecting the dynamics of social norms, as descriptive and prescriptive norms are likely subject to some shared as well as distinct selective pressures and processes of change. Throughout this work, I use Bayesian statistical inference to empirically test hypotheses on norm change. In chapter 1, I apply the framework of cultural evolution theory to examine how descriptive norms regarding perinatal care as promoted by the Red Cross spread among women in the Kunene region of Namibia. My analyses show that an observed shift towards medical recommendations regarding hospital birth and use of contraceptives is in line with predictions of conformity-biased social learning. In chapter 2, I employ sexual conflict theory to test whether women’s attitudes towards patriarchal gender norms in four East Asian populations reflect their anticipated fitness costs and benefits. I find that part of the variation in women’s attitudes towards gender norms may be explained through their varying interests in these prescriptive norms depending on their age and marital status. I further discuss how women’s social status may be protective against the costs of contesting culturally dominant norms. Lastly, in chapter 3 I propose an integration of cultural evolution and sexual conflict theory that I argue is crucial to understanding the complex relationship between gender norms and sexual conflict in humans.