Regularities and Diversity in Developmental Pathways: Mother–Infant Relationships in Hamadryas Baboons Marı ´a Victoria Herna ´ndez-Lloreda Departamento de Metodologı ´a de las Ciencias del Comportamiento Facultad de Psicologı ´a Universidad Complutense de Madrid Campus de Somosaguas 28223 Madrid, Spain E-mail: vhlloreda@psi.ucm.es Fernando Colmenares Departamento de Psicobiologı ´a Facultad de Psicologı ´a Universidad Complutense de Madrid Campus de Somosaguas 28223 Madrid, Spain E-mail: colmenares@psi.ucm.es ABSTRACT: Change, stasis, stability, discontinuity, orderliness, and diversity are all potential characteristics of developmental systems. This study uses multilevel modeling to characterize the normative developmental pathways of the early social relationships of 23 mother–infant pairs embedded in a multilayered colony of hamadryas baboons (Papio hamadryas hamadryas). The relationships were assessed by means of 27 behavioral measures that were collected during 100– 220 focal sampling sessions per infant, from birth to 380 days of age (25 two-week age intervals). Seventy four percent of the behavioral measures exhibited an age- related pattern. Infant age, however, was not predictive of the rate of the behaviors relating to the management of mother–infant conflicts. This study provides empirical evidence that the development of mother–infant relationships may involve periods of change and stasis, overall orderliness, and diversity as well as canalization of developmental pathways. We believe that growth curve analysis can be useful to tackle various hot issues in the study of behavioral development. ß 2005 Wiley Periodicals, Inc. Dev Psychobiol 47: 297–317, 2005. Keywords: developmental pathways; growth curve analysis; change; regularities; diversity; mother–infant relationships; hamadryas baboon INTRODUCTION Living systems, whether they consist of cells, organs, whole organisms, or groups of individual organisms, undergo changes over their lifetimes. Understanding how they develop during ontogeny and why they follow the particular developmental trajectories they do pose a major challenge in developmental science and in evolutionary biology (Bateson & Martin, 2000; Bateson, 2001; Gould, 1977; Gottlieb, 1992; Oyama, 2000). Animal behavior researchers interested in unraveling the principles that account for the development of an individual’s behavior or the relationship within a two-partner (or higher order) social system have struggled to develop conceptual and quantitative tools capable of capturing, assessing, and measuring its crucial properties and of testing hypotheses that provide a meaningful account of the processes that drive the patterns of stability and change observed during ontogeny (Bateson, 1983, 2003; Blass, 1986, 1988; Bryk & Raudenbush, 1987; Butterworth & Bryant, 1990; Chalmers, 1987; Gottlieb, 1992, 2001; Hall & Oppen- heim, 1987; Immelmann, Barlow, Petrinovich, & Main, 1981; Lewkowicz & Lickliter, 2002; Michel & Moore, 1995; Oyama, 2000; Oyama, Griffiths, & Gray, 2001; Turkewitcz, 1992; Willett, 1988). The conceptual framework adopted here is based on the developmental systems view, laid down by evolution- ary biologists (Hoo, 1998; Hood, 1998; Lewontin, 1983; Oyama, 1982, 2000), psychobiologists and comparative psychologists (Gottlieb, 1992; Johnston & Gottlieb, 2000), and ethologists (Bateson & Martin, 2000; Bateson, Received 15 February 2004; Accepted 8 June 2005 Correspondence to: F. Colmenares Contract grant sponsor: MEyC (Spain) (postdoctoral fellowship to FC (1988–1991) Contract grant sponsor: MCyT (Spain) (to FC) (project grants) Contract grant numbers: PB98-0773, BSO2002-00161 Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/dev.20104 ß 2005 Wiley Periodicals, Inc.