Nature vs. Nurture in Monkey Communication

This book describes the results of a cross-fostering
experiment to investigate the effects of experience
on emotional and informational content in rhesus
macaque (Macaca mulatta) vocal communication. The
subjects of the study were twelve rhesus macaques:
six were foster-reared by abusive mothers and six
were foster-reared by control mothers.
Vocalizations were recorded from the subjects in
their social groups for two years. The acoustic
variables measuring positive emotional expression
were lower in abused than control subjects. On the
other hand, abused subjects expressed exaggerated
levels of fear during mild contact aggression with
other animals. The second part of the study
statistically classified the calls of cross-fostered
monkeys to either their biological or foster
family. In the present study, matrilineal
signatures were clearly discriminated among
different families of rhesus macaques. Furthermore,
the calls of the majority of cross-fostered subjects
classified to the foster matriline, suggesting that
these signatures were learned rather than
inherited.