IPS title
 
 
     
 

Robert Walker Robert Walker
Postdoctoral Researcher

I am primarily a human behavioral ecologist, and my research attempts to understand behavioral and life-history variation among humans from a socioecological and evolutionary perspective (see PDFs below). My research and teaching goals focus on situating modern human variation in development, behavior and life-history against a backdrop of variation in other primates. For example, I am especially interested in using comparative analyses to study the evolution of long, slow-growing (yet large-brained) juvenile periods in humans as this is arguably the most derived human trait, driven by our early age at weaning and delayed growth spurt. In another line of inquiry, research with colleague Marcus Hamilton has uncovered a self-similar (or fractal-like) social structure in hunter-gatherer societies. Moreover, humans in a wide variety of contexts show increasingly efficient use of territory in larger populations which, along with the self-similarity in social structure, intriguingly suggest that human societies can be considered complex adaptive systems, perhaps even analogous to "super-organisms" in some regards.

In addition to statistical analyses and optimality modeling, I also enjoy fieldwork in South America. I have conducted research in Brazil, Paraguay, Bolivia, and Suriname with hunter-gatherers and subsistence horticulturalists. I loosely collaborate with an international team of researchers working around the globe and who share a common interest in quantifying age-specific rates of growth, fertility and mortality. My colleagues and I have found evidence that high mortality associates with population density, faster body growth, and earlier menarche and reproduction. There is also evidence for a trade-off between number and size of offspring across and within societies, an empirical pattern well-supported in other animals. I use these growing databases as a keystone for introducing students to a wide variety of topics that relate to the evolution of growth, senescence, mating and parenting. Opportunities abound in South America and around the world for students to conduct research in some of these ongoing fieldsites as well as develop new fieldsites in other communities. In my courses, I strongly encourage students to gain hands-on experience in data collection and analyses, placing confidence in their ability to conduct high-quality, publishable research.

Currently at the Max Planck Institute for Evolutionary Anthropology we are developing a general  agent-based model of primate demography to look at the effects of life-history, group size, and male reproductive skew as determinants of number and availability of kin in multi-male/multi-female societies. The model follows individuals from birth (to known parents) to dispersal (from the natal group and secondarily) to death (age/sex-specific, density-dependent mortality). Paternity is distributed across residents of a group according to a skew index (lambda) and male power, which depends on intrinsic differences and age. In a male dispersal model simulations yielded an accelerating relationship between male reproductive skew and dyadic within-group relatedness. We observed enormous effects of skew on relatedness at lambda indices between 0.85 and 1, where all offspring in a group in a year are sired by the alpha male. Surprisingly, across the main part of variation in male reproductive skew (lambda 0-0.85) the effect of skew on relatedness was weak. Likewise, variation in life-history traits including mortality, fecundity, age at first reproduction, and life span lead to surprisingly small changes in patterns of relatedness. Our results imply that in stable populations patterns of dyadic relatedness are similar for different primate species across a wide range of life-histories, group sizes and paternity concentrations and that consequently the potential for kin-selected behavior may vary little across most of the primate order.

 

Jr. Research Group Integrative Primate Socio-Ecology
Max-Planck Institute for Evolutionary Anthropology
Deutscher Platz 6
04103 Leipzig
Germany

Email: robert_walker (at) eva.mpg.de