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This chapter discusses the influence of a 1991 paper written by Richard D. Alexander, K. M. Noonan, and B. J. Crespi, in which they tackle the evolution of eusociality, particularly with regard to the importance of ecological constraints for human social evolution. It considers the evolution of sterility that characterizes classical eusocial species such as ants and naked mole-rats, along with its application to human societies. Alexander et al. emphasized the critical importance of ecological constraints in driving the evolution of cooperative breeding, and ultimately (in the extreme) the sterile castes of eusociality. This line of thinking can be traced to Alexander's much earlier papers, such as his classic 1974 paper on the evolution of social behavior. In turn, Alexander's arguments in this vein led to the development of an entire branch of theory within behavioral ecology. This chapter includes an excerpt from the 1991 paper by Alexander, Noonan, and Crespi entitled “The Evolution of Eusociality” and published in The Biology of the Naked Mole-Rat.

This chapter reviews selected aspects of the anatomy and physiology of treeshrews that are especially pertinent to their ecology. It suggests that the teeth and digestive tracts of treeshrews are similar to those of many other insectivorous mammals, and that they possess a number of both primitive and more derived features. The chapter describes the sensory skills of treeshrews and argues that their body size may have tight ecological constraints. It also reflects on treeshrews' social behavior.

This chapter presents an excerpt from a classic paper on the evolution of eusociality, written by Richard D. Alexander, K. M. Noonan, and B. J. Crespi and published in 1991 in an edited volume entitled The Biology of the Naked Mole-Rat. It relates the story of how Alexander conceived of the key characteristics of a eusocial vertebrate as a thought experiment and prediction before anyone was aware of the existence of such an animal. Alexander's description almost perfectly fit the naked mole-rat. In their paper, Alexander et al. made several key points with respect to the evolution of eusociality: first, the haplo-diploid system that characterizes the major eusocial insects (ants, bees, and wasps) is not a sufficient explanation for the evolution of eusociality; second, eusociality is a much more general phenomenon than initially believed; and third, both intrinsic and extrinsic factors must have been crucial for the evolution of eusociality. They also argued that both “ecological constraints” in the form of the need for nest site protection from predation and levels of genetic relatedness (kinship) are crucial for the evolution of eusociality.

The focus in this chapter is on why honor killing ever came into existence as a social practice. The units for analysis are sociocultural systems and ecological pressures on the demographic groups among whom honor killing evolved. Here a population-level model of cultural evolution is employed to advance an argument for the best explanation for the development of honor killing. Only cultural systems performing adaptive functions continued among early desert nomads and pastoralist of the arid mountain uplands. Historical and anthropological research supports claims that severe ecological challenges led to two major functional systems: consanguine hierarchical patriarchy and the segmentary lineage system. Honor killing likewise evolved, first as a costly signaling system to avert loss of female reproductive assets and to avoid group splintering. It later evolved further as an exaptation and as a means of avoiding blood-related conflicts within segmentary lineage systems.