The “Hippie” Monkeys

          In patches of forests along the Atlantic coastline of Brazil, there live an amazing species of monkeys known as the muriqui.  They are amongst the rarest species of monkey in the world, with a small habitat that is still decreasing.  They are the largest species of monkey found in Brazil and all of South America.  In Shannon Brownlee’s article “These Are Real Swinging Primates”, Brownlee presents research done by herself and Beloit College professor Karen Strier.  The hypothesis that Strier formulated and Brownlee presents is a simple one: the muriqui have evolved in the ways they have due to their “need to avoid falling out of trees” (Brownlee, p 72).  The muriqui evolved over time into the creatures they are today because the environment forced biological changes on them.  These changes influence the way the muriqui behave.
          Strier gets most of her data from field observations.  When she started studying the muriqui in 1981, she first had to acclimate the muriquis to her presence, which she found difficult, as the muriqui do not take kindly to being followed.  She still finds it difficult to observe them in the field because the muriquis move so much in a day.  It is also difficult because the muriqui are arboreal creatures, and the underbrush of their habitat tends to be thick.  She discovered that the muriqui are an extremely peaceful species who only defend favored food sources and do not fight over mates.  In fact, many males will patiently wait in line to attempt to impregnate one female of the species.  These creatures do live in social groups, mixed with both males and females.  It is interesting to note that both the male and the female of the species are almost the same size. (Brownlee, pg 72-76)
          Based on this data, Strier made the several conclusions concerning the muriqui.  Among these were the reasons that the male and the female of the muriqui species are the same size.  One of these reasons is this: in order to be able to swing quickly from branch to branch in the rainforest, a creature must be of a certain size, and the muriqui could not get larger without losing this ability.  This causes a very large limitation on the size of the muriqui.  Another fascinating conclusion was the reason behind the peaceful nature of the species.  The muriqui really cannot afford to fight for two major reasons, the first that falling out of trees is never a good thing, and the second being that spending the amount of energy that it would take to fight is just not feasible in their situation as food is often at a premium.  Because the males do not fight over mates, their size remains small.  The fact that males of the species do not fight over mates has a very large part to do with how they evolved large testicles.  Females of the species will mate with more than one male, and the larger the testicles, the more sperm a male can produce.  By producing more and better sperm, a male increases his chances of impregnating a female and thus passing on his genetic traits to the next generation.  These conclusions link the socioecological and sociobiological approaches to primate behavior.  These creatures have evolved due to their environment, and both the environment and their biology is affecting their behavior as a species.  Strier’s original hypothesis was indeed at least partially correct. (Brownlee, p 72-76)

I found this article hard to follow sometimes, and there was information that perhaps was unnecessary to understand the article.  The first time I read it, I found it quite hard to pick up on what the article was actually focusing on.  Upon further study, it began to become clear to me what the article was really discussing.  I find Strier’s research fascinating and I wonder if the muriqui are the only species that have evolved in this way.  I also wonder if they are the only species to illustrate the links between socioecology and sociobiology in relation to primate behavior.  I liked Brownlee’s approach to presenting Strier’s research; as Brownlee traveled to Brazil to actually observe the muriqui before writing the article; the firsthand experience seems to add something to the article.


Works Cited

Brownlee, S (2000) These Are Real Swinging Primates.  In, Angeloni E (ed) Annual Edition: Physical Anthropology: 72-76.  Dushkin Pub. Group. Inc: Guilford, CA.