82 Diet and culture at Sonso
As McGrew (1998: 319) states:
The hand clasp occurs daily at Mahale but has never been seen in more than 35 years of observation at
Gombe. It also is customary at Kibale and Taï but not at Bossou (Boesch and Tomasello 1998). At
Kibale it is common both in the Kanyawara community and in the Ngogo community (Watts, personal
communication). Interestingly, the pattern has now emerged in a captive group at Yerkes, where it is
spreading from its first performance by a captive-born adult female (de Waal and Seres 1997).We can now add Budongo to the list of sites at which hand-clasping does not occur;
we have never seen it at Sonso. And from the distribution of this item of chimpanzee cul-
ture we can see that it has not spread by diffusion; indeed, the observation of its origin
at Yerkes shows it is capable of independent origination at multiple sites.
There are other anomalies. Leaf-sponging (drinking water using a crumpled leaf to
soak it up and then squeezing it into the mouth) is in one sense not a cultural trait
because it occurs at all sites and is thus a universal (Whiten et al. 2001); however, these
authors state that in time it may be considered as a cultural variant because of differ-
ences in the ways or the contexts in which it is done. This seems correct, in the same
way that whereas eating itself is not a cultural activity for humans, how we eat, when we
eat, and what we eat are all very cultural indeed. We shall return to leaf-sponging below.
Leaf-clipping with the teeth (biting bits off a leaf held in one hand) is of interest because
this behaviour has different functions in East and West Africa: in East Africa, at Sonso and
at Mahale (Nishida 1980) it is found in the context of courtship behaviour, with males
(including subadult and even juvenile ones) doing this to try to attract the attention of sexu-
ally attractive females. In Taï it occurs before buttress drumming and at Bossou it is done
to attract a playmate; at neither site does it occur in the courtship context (Boesch 2003).
In one cultural feature the Sonso chimpanzees differ from those at other sites: penile-
cleaning is particularly common. Adult Sonso males engage in this to a greater extent
than do males at other sites. Sean O’Hara observed 116 copulations of which penile-
wiping occurred in 34.5% of cases, and penile-cleaning with leaves in 9.5% of cases.
The use of leaves is more common at Sonso than at Gombe where the frequency is
2.9%, and at Kanyawara in Kibale Forest where it is 2.2%. At Mahale, Bossou and Taï
penile-cleaning with leaves has not been observed at all (O’Hara and Lee, in progress).
The question of how cultural items are transmitted raises a number of problems and
I shall not deal with them here. There is little evidence for teaching in chimpanzees, and
much for observational learning. We have seen how chimpanzee infants learn from their
mothers what foods to eat; most people are familiar with the way young chimpanzees at
Gombe learn termite fishing by watching their mothers, and the way chimpanzees
at Bossou and Taï learn nut-cracking by watching their mothers, so very likely most
cultural activities are learned by observation of mothers and other individuals in
the community. The actual process of learning is hard to document in the wild but
Andy Whiten has devised an ingenious experiment to demonstrate how traditional
processes are handed on in captivity and semi-captive situations. These, and the topic of
social learning generally, are dealt with at length by Whiten et al. (2003).