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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10.00

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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1997;275:797-804. Reader SM, Laland KN. Social intelligence, innovation, and enhanced

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.