Mothers and Others is a highly stimulating essay on the evolutionary origins of human empathy, i.e. being curious and concerned about the emotions of others. Ultimately, understanding why humans show extreme intersubjectivity is crucial in discussing the evolutionary origins of large-scale cooperation – a perennial hot topic for many evolutionary anthropologists. In this context, Sarah Hrdy challenges the current dominant view that the main selective pressure for the evolution of cooperation within a group is inter-group competition. She argues that, ‘We have underestimated just how important shared care and provisioning of offspring by group members other than parents has been in shaping social impulses.' Using a broad comparative perspective, she aims to demonstrate that cooperative breeding is a pre-existing condition that permitted the evolution of key human traits such as extended lifespan, prolonged childhoods and bigger brains. However, as is often the case for the big questions in behavioural science, the accumulation of evidence does not always prevent circularity of reasoning, leading some core questions of the book (i.e. why us and not them [apes]?) partly unanswered. Consequently, Mothers and Others should be viewed as a case for alternative views and critical thinking of current theories rather than a problem-solving dissertation. Although Mothers and Others makes the case for a role of cooperative breeding in shaping cognitive traits allowing individuals to show empathy, even toward non-related individuals, it does not explain why hypersociality has evolved in humans. Nonetheless, this incredibly well documented book (>800 references) has great merit, brilliantly integrating knowledge from child development, psychology, primatology and behavioural ecology, and in doing so provides a unique opportunity to rethink the evolutionary history of the human family.

The argument for the role of cooperative breeding in shaping pro-social impulses and subsequent key human features (i.e. our big brain) builds on the fact that apes, although possessing the basic brain equipment to infer other's motivations, have not evolved hypersociality. ‘So why us and not them [apes]?' Hrdy asks. If pro-social impulses allow groups to outcompete others, then a highly competitive species such as chimpanzees would surely have benefited from such an ability, and selection should have favoured pro-sociality and big brains in this species. One important point this reasoning makes is that considering apes as a model to understand human cooperative behaviour is not necessarily a good starting point. Rather, using analogies based on social system rather than phylogeny allows us to observe a joint occurrence of cooperative breeding and pro-social impulses cross-species, and ultimately consider the possibility that pro-social impulses have been selected for as a result of cooperative breeding. However, the question remains: why us and not them (i.e. the cooperative breeding species)? Why have high social skills and associated big brains only evolved in humans and not in Callitrichidae, for instance? Hrdy argues that, ‘The remarkable thing about humans is not so much cooperative breeding as it is cooperative breeding in an ape, … in a primate already possessing the cognitive capacities, Machiavellan intelligence, and incipient theory of mind typical of all great apes.' Then, one cannot rule out that if theory of mind is a pre-existing condition for cooperative breeding to select for hypersociality, then the selective pressures for the evolution of theory of mind, so far believed to be inter-group competition, might still be relevant to account for the evolution of human cooperation. Then, whether cooperative breeding is necessary at all for the evolution of human hypersociality can be questioned. If it is likely that cooperative breeding increases the amount of energy available for individuals, as Hrdy suggests, and thus relaxing constraints on the evolution of energetically costly organs such as brains, other mechanisms could do the job, i.e. the development of cooking and subsequent high energy food. Finally, it is still possible that the benefit associated with having of a large brain has selected for an extended juvenile period and subsequently for cooperative breeding. Although Hrdy recognizes the occurrence of co-evolutionary processes, the argument would have benefited from more emphasis on ‘why humans and no other cooperative breeders’, i.e. what is the ecological parameter specific to humans, as compared with all other species, that has selected for high levels of pro-sociality?

One appreciable input of Mothers and Others is the critique of taken-for-granted arguments. For instance, using the ‘misplaced parental investment’ hypothesis and evidence that care is not always directed towards kin, she questions the over-reliance on genetic relatedness to explain observed patterns of alloparental care. This emphazises that ecological circumstances (e.g. distribution of resources) are critical in explaining the expression of altruistic behaviour, and those must not be overlooked. In this line, Hrdy challenges the traditional view of the Pleistocene human reproductive system. She provides evidence that polyandry is likely to have been common in ancestral time, and thus the conflict between men and women over reproduction not always in favour of men across our evolutionary history. Using both genetic and cross-cultural data, she argues that the common assumption of ancestral patrilocal residence is far from certain, and sex dispersal more likely to be highly flexible. This has implications for how we discuss the evolution of key human traits such as women's early cessation of reproduction (i.e. menopause) as a helping behaviour, and to generally reconsider the male-payoff maximization view of the early environment and associated selective pressures. Interestingly, the ecological and historical perspectives of the book raise an important question. How much can contemporary human populations tell us about our evolutionary past? It is often assumed that hunter-gatherers are the most likely to inform us on early environment and past selective pressures. However, ecology has changed since the Pleistocene, and, as Hrdy recognizes, recent genetic evidence shows that evolution didn't end at the Neolithic revolution, with natural selection still operating, even accelerating in humans. Thus, current selective pressures do not necessarily inform on past selective pressures. As a consequence, one might question the extent to which the knowledge of non-Western contemporary populations is helpful to infer the ancestral human family, and to what extent the knowledge of the human family during the Pleistocene informs us on current behaviour.