Imo's mother Eba was the first to mimic the potato washing. Females in the troop were more likely to wash their sweet potatoes than older males. Remember that when they become old enough to mate, male macaques leave the troop, meaning they have less social interaction with their original troop members. Without that integral social interaction and exposure to the new behavioral patterns in a group setting, the older males didn't pick up the habit [source: Carpenter].
Age also played an important role in whether monkeys would wash their potatoes. In general, monkeys younger than the age of two were quicker to try something new. This is because of the inverse relationship between age and brain plasticity -- the brain's ability to create new neural connections required for learning -- which allows us to acquire new skills [source: Carpenter]. Additional behavioral studies with macaques correlated with this age gradient, as the youngest members show the most innovation and least conservatism.
A similar adaptation pattern occurred when testing if the monkeys would try caramel candy. The juvenile and infant macaques paved the way as they were the first ones to eat the candy that researchers gave them. Adults followed suit, as an example of observational learning in monkeys.
The sweet potato washing remained confined to the one macaque troop on the island of Koshima [source: Baumeister]. Nevertheless, Imo's clever idea sparked a novel way of thinking about how animals interact. For more information about monkeys, visit the links below.
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- Barker, Dennis. "Obituary: Lyall Watson." The Guardian. July 23, 2008. (July 24, 2008) http://www.guardian.co.uk/science/2008/jul/23/pressandpublishing?gusrc=rss&feed=books
- Baumeister, Roy F. "The Cultural Animal: Human Nature, Meaning and Social Life." Oxford University Press US. 2005. (July 24, 2008) http://books.google.com/books?id=NvUdksYzQRUC
- Carpenter, Clarence Ray. "Behavioral Regulators of Behavior in Primates." Bucknell University Press. 1973. (July 24, 2008) http://books.google.com/books?id=RiOgcvMEioUC
- Fa, John E. and Lindburg, Donald G. "Evolution and Ecology of Macaque Societies." Cambridge University Press. 1996. (July 24, 2008) http://books.google.com/books?id=5BoM1Z3K1DsC
- Gron, Kurt. "Japanese macaque (Macaca fuscata)." National Primate Research Center. April 26, 2007. (July 24, 2008) http://pin.primate.wisc.edu/factsheets/entry/japanese_macaque/taxon
- "History of Salt." UK Food Standards Agency." (July 24, 2008) http://www.salt.gov.uk/history_of_salt.html
- Ryall, Julian. "Chunky monkey put on diet at Japanese park." The Telegraph. May 6, 2008. (July 25, 2008) http://www.telegraph.co.uk/news/worldnews/asia/japan/1929251/ Chunky-monkeys-put-on-diet-at-Japanese-park.html
- Tanhehco, Ed. "Macaca fuscata." Animal Diversity Web. (July 24, 2008) http://animaldiversity.ummz.umich.edu/site/accounts/information/Macaca_fuscata.html