origins of simian intelligence the licking to picking hypothesis alex dunkel exotic animal training...
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Origins of Simian Intelligence
The Licking to Picking Hypothesis
Alex DunkelExotic Animal Training & Management Program, Moorpark College
Comparing Primates
Simians: monkeys and apes Most simians are social Considered more intelligent
Have larger neocortex Groom manually
Prosimians: lemurs, lorises, tarsiers, etc. Some are social, others solitary Considered to be less intelligent Groom orally
Existing Hypotheses
Foraging Hypotheses Examine correlation
between ecology and brain size
Have difficulty identifying the selective force by which simian intelligence evolved
Most implicate brain structures other than the neocortex
Not widely accepted
Existing Hypotheses (con.)
Social Hypotheses Widely accepted and popularized
Extended to other mammalian orders Focus on complexity of social
behavior and group size Shortcomings:
Do not sufficiently explain fidgeting and the manipulation of objects
Inadequately explain why social lemurs lack the intelligence the hypotheses predict
The Licking to Picking Hypothesis
Defining aspects of primate intelligence Manual manipulation of non-food items is key to our
intelligence and ability to learn about our environment This requires highly dexterous appendages to
manipulate objects, along with a drive to do so The Licking to Picking Hypothesis:
A change in grooming style (from licking to picking) generalized to inanimate objects → fidgeting
Fidgeting resulted in non-foraging manipulation, while insight learning, abstract thought, and social learning (from the social hypotheses) created avenues for the creation and sharing of novel adaptive behaviors
Strepsirrhini
Lemurs Lorises
common primate ancestor
TarsiersNew WorldMonkeys
Old WorldMonkeys Apes
Haplorrhini
Prosimians Simians
Licking to Picking (con.)
Change in grooming style occurs sometime after the split with tarsiers
All descendant simians groom manually and manipulate non-food objects
All descendant prosimians groom orally and do not manipulate non-food objects
Licking to Picking (con.)
Simian intelligence is multifaceted Our tool use comes from our manipulation of
non-food items, with new behaviors propagated through social learning
Abstract thought and insight learning are separate, but overlapping types of intelligence
This hypothesis is part of a more general view on the evolution of intelligence The evolution of complex systems usually
requires preadaptations. Intelligence is no exception!
Licking to Picking (con.)
In general terms, this hypothesis works with the social hypotheses to better explain the full gamut of animal intelligence. (They are inclusive!)
Social Solitary
most simians, some corvids, elephants, social lemurs, hyenas, lions, psittacines,
rats, dolphins, domestic dogscephalopods, raccoons, orangutans
The general concept, when used with the social hypotheses, explains the lack of object manipulation and fidgeting in social lemurs, but also explains intelligence gradients in other social animals.
It better explains the intelligence of solitary animals, such as orangutans, cephalopods, and raccoons
Circumstantial Evidence
Grooming behaviors are sometimes seen in simians during manual problem solving
Fidgeting may possibly be related to intelligence in humans
Fidgeting behaviors often include grooming behaviors Playing with hair Rubbing hands together Biting fingernails
Research Overview
Observed social groups of various primates Counted instances of specific behavior types:
Oral grooming Manual grooming Foraging manipulation
Non-foraging manipulation Manual prehension Oral prehension
Compared the frequency of behaviors between simians and prosimians
Observed species:
Propithecus verreauxi coquereli
Varecia variegata rubra
Lemur catta Pan troglodytes Cebus apella Colobus guereza
Research Obstacles
Clearly defining behavior criteria Counting instances of varying duration
e.g. Prehension of small vs. large food items What constitutes “non-foraging manipulation?” Ambiguities in grooming definitions
Does scratching qualify as grooming? Simian oral grooming
Enrichment and enclosure design restrictions for simians affected observations
Resultsforaging manipulation
non-foraging manipulation
manual prehension
oral prehension
oral grooming
manual grooming
ProsimiansLemur catta 1.13 0.00 5.88 4.65 5.80 0.00Propithecus verreauxi coquereli 1.18 0.00 11.30 5.98 2.40 0.00Varecia variegata rubra 0.33 0.04 0.85 4.17 5.52 0.00Averages 0.88 0.01 6.01 4.93 4.57 0.00
SimiansPan troglodytes (exhibit) 0.16 0.44 5.62 0.04 0.02 1.92Pan troglodytes (penthouse) 0.67 4.48 7.24 0.00 0.14 5.00Cebus apella 8.61 5.39 14.61 1.13 0.61 5.61Colobus guereza 1.30 0.50 6.96 0.21 0.14 4.96Averages 3.53 3.46 9.60 0.45 0.30 5.19
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Instancesper Individual
per Hour
foragingmanipulation
non-foragingmanipulation
manualprehension
oral prehension oral grooming manual grooming
Behavior Type
Behavioral Comparisons
Simian
Prosimian
Conclusion
Primates that groom manually also manipulate non-food items and use their hands more for food acquisition
Correlation does not imply causation Much more research is needed Need to look at the fossil record to see if more
dexterous hands evolved when grooming changed
The following facilities graciously accommodated my observation time: Duke Lemur Center Los Angeles Zoo & Botanical Gardens America’s Teaching Zoo at Moorpark College
Special thanks to the following people for their feedback and support: Gary & Cindy Wilson
Acknowledgements
And, of course, my troop – two very special lemurs who pointed out the obvious and inspired my research
Obi & Janga
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brain size in primates. PNAS. 2002;99:4436-4441. Rifkin, SA. The Evolution of Primate Intelligence. Brain. 1995;2.
Available at: http://kim.bio.upenn.edu/~scott/Papers/Rifkin1995Brain.html. Accessed February 2, 2008.
Santos LR, Mahajan N, Barnes JL. How prosimian primates represent tools: Experiments with two lemur species (Eulemur fulvus and Lemur catta). Journal of Comparative Psychology. 2005;119:394-403.