Contingency (or “luck”) in early life plays an important role in shaping individuals’ development. By comparing the developmental trajectories of functionally genetically identical free-living mice wh...

Animals, and mammals in particular, vary widely in their “pace of life,” with some species living long lives and reproducing infrequently (slow life histories) and others living short lives and reproducing often (fast life histories). These species also vary in the importance of maternal care in offspring fitness: in some species, offspring are fully independent of their mothers following a brief period of nutritional input, while others display a long period of continued dependence on mothers well after nutritional dependence. Here we hypothesize that these two axes of variation are causally related to each other, such that extended dependence of offspring on maternal presence leads to the evolution of longer lives at the expense of reproduction. We use a combination of deterministic modeling and stochastic agent-based modeling to explore how empirically-observed links between maternal survival and offspring fitness are likely to shape the evolution of mortality and fertility. Each of our modelling approaches leads to the same conclusion: when maternal survival has strong impacts on the survival of offspring and grandoffspring, populations evolve longer lives with less frequent reproduction. Our results suggest the slow life histories of humans and other primates as well as other long-lived, highly social animals such as hyenas, whales, and elephants, are partially the result of the strong maternal care that these animals display. We have designed our models to be readily parameterized with demographic data that is routinely collected by long-term researchers, which will facilitate more thorough testing of our hypothesis. Significance Statement Humans and other primates live longer lives and reproduce less often than other mammals of similar body mass. What is the cause of these long lives? Here we add to existing hypotheses, including the Mother and Grandmother hypotheses, by arguing that these increased lifespans are partially explained by the intense maternal care that many primates express. Using a combination of deterministic and stochastic modeling approaches, informed by empirical data, we show that stronger connections between maternal survival and offspring fitness leads to selection for longer lives and slower reproduction. Our models suggest that the importance of the mother-offspring relationship, which defines much of human and non-human primate lives, lies at the core of the evolution of our long lives. ### Competing Interest Statement The authors have declared no competing interest.

Do animals have emotions? Scientists and philosophers have long struggled with this question, with debates ranging from whether animals experience an “internal world” to whether we are capable of studying it. Recently, theoretical, and methodological advances have rekindled this debate, yet, it is unclear where the scientific consensus on these topics lies today. To address this gap, we administered a survey of professional animal behavior researchers to assess perceptions regarding ([1][1]) the taxonomic distribution of emotions and consciousness in non-human animals, ([2][2]) respondents’ confidence in this assessment, and ([3][3]) attitudes towards potential for progress and possible pitfalls when addressing these questions. In general, animal behavior researchers (n=100) ascribed emotionality and consciousness to a broad swath of the animal taxa, including non-human primates, other mammals, birds, and cephalopods, with varying degrees of confidence. There was a strong positive relationship between how likely a respondent was to attribute emotions to a given taxa and their confidence in that assessment, with respondents assuming an absence of emotions and consciousness when they were unsure. In addition, respondents’ assessments were shaped by several traits (e.g., advanced cognitive abilities, consciousness) that they also admitted were not necessary for an animal to experience emotions. Ultimately, a large majority of researchers were optimistic that tools either currently exist or will exist in the future to rigorously address these questions (>85%) and that animal behavior, as a field, should do more to encourage emotions research (71%). We discuss implications of our findings for publication bias, ethical considerations, and identify an emergent consensus for the need of a functional definition of emotions to facilitate future work. Significance Statement Emotions and consciousness are fundamental components of human experience—these phenomena are central to our behavior, relationships, and sense of meaning. Whether these experiences are shared by non-human animals has long been a subject of philosophical and scientific debate. In this paper we describe, for the first time, results from a survey of animal behavior researchers regarding their perceptions of these questions and the ability of science to answer them. Researchers ascribe emotions and consciousness to many taxa, and their likelihood of doing was strongly predicted by phylogeny and researchers’ confidence in their answers. We hope these results spur additional interdisciplinary collaboration to rigorously pursue these questions and create a baseline for future comparisons to track scientific attitudes over time. “I have chosen bats instead of wasps or flounders because if one travels too far down the phylogenetic tree, people gradually shed their faith that there is experience there at all”--Thomas Nagel ### Competing Interest Statement The authors have declared no competing interest. [1]: #ref-1 [2]: #ref-2 [3]: #ref-3