1. Andrew, R. J. The origin and evolution of the calls and facial expressions of the primates. Behaviour, 1963, 20, 1 – 109.
2. Baldwin, J. D., & Baldwin, J. I. Vocalizations of howler monkeys (Alouatta palliata) in southwestern Panama. Folia Primatologica, 1976, 26, 81 – 108.
3. Bell, S. M., & Ainsworth, M. D. Infant crying and maternal responsiveness. Child Development, 1972, 43, 1171 – 1190.
4. Bowlby, J. The nature of the child’s tie to his mother. International Journal of Pediatrics, 1958, 39, 350 – 373.
5. Chevalier-Skolnikoff, S. The ontogeny of communication in the stumptail macaque (Macaca arctoides). Contributions to Primatology, 1974, 2, 1 – 174.