Left-cradling bias is a distinctive feature of maternal behaviour in humans and great apes, but its evolutionary origin remains unknown. In 11 species of marine and terrestrial mammal, we demonstrate consistent patterns of lateralization in mother–infant interactions, indicating right hemisphere dominance for social processing. In providing clear evidence that lateralized positioning is beneficial in mother–infant interactions, our results illustrate a significant impact of lateralization on individual fitness.
We thank the administration of the protected areas where data were collected for their cooperation and support. We thank A. Smorkatcheva, A. Vashurkina, V. Kalmikov, A. Kochnev, K. Leggett and S. Nicol for help in the organization of the field studies. The collection of data on lateralization in Pacific walrus, Siberian tundra reindeer, argali and southern right whales (inspection of aerial photographs), and all analytical work, was funded by the Russian Science Foundation (grant no. 14-14-00284). Field studies on grey and red kangaroos were supported by the National Geographic Society Committee for Research and Exploration (grant no. 9261-13). Field studies on saiga antelope, muskox and feral horses were supported by the Russian Foundation for Basic Research (grant no. 14-04-31390), and Saint Petersburg University (grant no.1.42.508.2013). The data on southern right whales were provided by Ocean Alliance and the Instituto de Conservacion de Ballenas, and were collected under research permits from the Dirección de Fauna y Flora Silvestre and the Subsecretaría de Turismo y Áreas Protegidas of Chubut Province, Argentina. Work was conducted with the approval of each protected area’s authorities and St Petersburg State University ethical committee (permit no. 131-03-5).
Supplementary Tables 4–14