Intelligence and Fitness Mutuality in Cappucine Monkeys
- From: "John Edser" <edser@xxxxxxxxxxxxxx>
- Date: Mon, 23 Oct 2006 12:00:13 -0400 (EDT)
Capuchin monkeys live in groups of about 40 with a highly evolved social
structure. One of their most important food items are nuts. They test them
by tapping and strip those that have the correct ripeness dropping them onto
the forest floor where they harden over time. Some of these hardened nuts
are carried to rock anvils which can be located miles away. These anvils
have become worn from centuries of use displaying depressions of various
sizes which fit different sized nuts. The monkeys select the correct
depression and attempt to crack the nut with a smooth river stone which may
have also been carried to the anvil site from miles away. Many of these
river stones, each a different size and shape, were observed at anvil sites.
The nut cracking harvesting and cracking technique which is complex is
passed on from generation to generation by learning. The monkeys appear to
work in a rational fashion. The scattered hardened nuts provided by the
troop can be taken by any individual. These are replaced with newly
harvested unhardened nuts as the hardened variety are processed and eaten.
Over time the individuals in one troop coordinate together to maintain a
constant supply of hardened nuts for common use.
In experimental situations these monkeys share their spoils. If nuts become
placed in a sealed jar with a covering that could only be broken by a tool
e.g. a flint stone, where one monkey had the stone and the other the jar of
nuts where they remain separated by a partition with an arm sized hole for
communication, the monkey with the stone tool will pass it to the monkey
with the nuts so that it can bust open the jar. The stone receiving monkey
will then pass back some of the nuts. Cheating was not observed. This
behavior is obviously mutualistic but does not necessarily constitute
cognitive mutualised exchange (commonly referred to as "trade") because
exchange solicitation which requires bargaining were not observed. After
viewing the situation the monkey with the stone simply passes it to the
monkey with the jar of nuts who then passes some of the nuts back.
Can cheating evolve in any one of these highly mutualised forms of behavior?
Could hardened nut collecting for individual consumption but evasion of all
the collective hard work of nut testing and stripping be selected for? Could
an individual evolve to use the stones but avoid stone carrying? Could the
monkey with the jar of nuts be selected to fail to return some of the food
obtained by the use of the stone tool provided by the other monkey in the
observed experiment? If so, how?
Revue / Journal Title
American journal of primatology (Am. j. primatol.) ISSN 0275-2565 CODEN
AJPTDU
Source / Source
2004, vol. 64, no4, pp. 359-366 [8 page(s) (article)] (15 ref.)
"We conducted an exploratory investigation in an area where nut-cracking by
wild capuchin monkeys is common knowledge among local residents. In addition
to observing male and female capuchin monkeys using stones to pound open
nuts on stone anvils, we surveyed the surrounding area and found physical
evidence that monkeys cracked nuts on rock outcrops, boulders, and logs
(collectively termed anvils). Anvils, which were identified by numerous
shallow depressions on the upper surface, the presence of palm shells and
debris, and the presence of loose stones of an appropriate size to pound
nuts, were present even on the tops of mesas. The stones used to crack nuts
can weigh > 1 kg, and are remarkably heavy for monkeys that weigh <4 kg. The
abundance of shell remains and depressions in the anvil surface at numerous
anvil sites indicate that nut-cracking activity is common and long-enduring.
Many of the stones found on anvils (presumably used to pound nuts) are river
pebbles that are not present in the local area we surveyed (except on or
near the anvils); therefore, we surmise that they were transported to the
anvil sites. Ecologically and behaviorally, nut-cracking by capuchins
appears to have strong parallels to nut-cracking by wild chimpanzees. The
presence of abundant anvil sites, limited alternative food resources,
abundance of palms, and the habit of the palms in this region to produce
fruit at ground level all likely contribute to the monkeys' routine
exploitation of palm nuts via cracking them with stones. This discovery
provides a new reference point for discussions regarding the evolution of
tool use and material culture in primates. Routine tool use to exploit
keystone food resources is not restricted to living great apes and ancestral
hominids."
John Edser
edser@xxxxxxxxxxxxxx
.
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