II. All the species of the family have a wide variety of "displays" — — ritualized 
social signal patterns 
III. Some species seem to employ olfactory signals. Ihese have not been studied in 
any detail# Apparently usually used to facilitate specific and individual recognition# 
Strange animals introduced to one another for the first time usually sniff at one another 
immediately. The initial reaction# Sometimes done in a very rigid and formalized manner# 
Olfactory signals of various types are also associated with sexual behavior in a few 
species# 
IV# All the species are extremely vocal# Vocal patterns always or almost always the 
most important (and most frequent) signals# 
The vocal patterns of most species range from thin, high-pitched, squeaks and whistles 
to low-pitched (and usually loud) barks, grunts, and roars# All the vocal patterns appear 
to be produced when two or more different types of motivation are in conflict and/or when 
one type of motivation is thwarted# The vocal repertories of different species are 
superficially very different ; but they are (largely) composed of homologous elements# 
By comparing the vocal repertories of different species, it may be possible to 
determine the "basic" vocal repertory of the family as a whole# 
The differences between the vocal repertories of different species seem to ne due 
to a few relatively simple changes in the course of evolution; 
1# An increase in the number of distinct patterns (division)# 
2# Different inter-connections between patterns# 
3# Loss of some patterns (not fusion)# Example: Squ - Wh# 
r 
4« General changes in tone. Examples: 
a# Howler monkeys# All grunts, barks, roars (as adults), 
b# Marmosets. All bird-like squeaks and whistles# 
5# Changes in the thresholds at which transitions between different tones and/or 
rhythms occur# Examples: 
