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[Andrew Hund <andrew.hund AT cwru.edu>]

http://news.nationalgeographic.com/news/2004/06/0604_040604_lemurs.html#main

John Pickrell in England
for National Geographic News
June 4, 2004


We already know that monkeys and apes have remarkable levels of intelligence. 
Chimps and gorillas have been taught to use complex sign languages, Rhesus 
macaques demonstrate knowledge of basic math, and baboons are known to 
commonly deceive one another to their own ends. 
But lemurs— monkeys' primate cousins—were thought to possess few of these 
abilities. Scientists had all but written them off as a cognitive dead end in 
the primate family tree. 

Now, Aristides, an 11-year-old ring-tailed lemur with fluffy gray fur and 
enquiring brown eyes, may be about to turn that idea on its head. 

With the help of his trainer, psychologist Elizabeth Brannon, Aristides 
selects sequences of images by pressing his nose against a computer screen. 
In return for fruit-flavored sugar pellets, Aristides and his eager 
classmates at the Duke University Primate Center are providing Brannon's team 
with compelling clues about how our earliest primate ancestors developed 
mental capabilities that we all share today. 

Ancestral Brainpower 

Fossils suggest that lemurs, bush babies, lorises, aye-ayes, and their 
relatives (the prosimians) spilt off from the ancestors of monkeys and apes 
around 55 million years ago. Therefore studying the brainpower of these 
seemingly primitive animals might offer insights into the earliest primates' 
mental abilities. 

"Anthropologists are interested in discovering how human intelligence evolved 
and how we differ to other species," said Brannon of the Durham, North 
Carolina-based university. "By pinpointing which cognitive abilities all 
primates share, including prosimian primates, we hope to determine what 
aspects of intelligence are general primate adaptations." 

Much of Brannon's research has focused on understanding how humans became so 
sophisticated numerically. Her studies of human infants, monkeys, and now 
lemurs are helping to piece together a picture of whether primates possess a 
special predisposition to math. 

Despite the huge quantity of literature on all aspects of intelligence in 
chimpanzees, rhesus macaques, and a handful of other primates, there has been 
very little work on lemurs. Brannon's work may now go someway to filling that 
frustrating data hole. 

However, she started the pilot project with low expectations. Lemurs—which 
are found exclusively on the African island of Madagascar—are much less 
curious than the average monkey. The handful of existing cognitive studies 
suggested that the animals had little capacity to learn or complete simple 
tasks. 

List Learning 

Nevertheless, Brannon's project has already yielded some encouraging results. 

In one trial the Duke University team is testing the star pupil Aristides' 
ability to remember longer and longer lists of photographic images displayed 
on the computer monitor. His classmates—another ring-tailed lemur called 
Teres and two mongoose lemurs (distinguished by their white snouts and 
red-brown beards), Miguel and Guillermo—are also eager to complete the same 
tasks for banana- or tropical fruit-flavored rewards. 

Through trial and error, the lemurs are quickly learning to tap out lists of 
images of snails, houses, trees, cars, mountains, and other brightly colored 
photographs. The lemurs are also able to correctly order pairs of pictures 
from the sequence, suggesting that they are able to work through the list in 
their minds. 

"We've been finding that ring-tailed lemurs are very good at this task and so 
far perform similarly to monkeys in terms of their accuracy and response 
times," Brannon said. "One big difference is that lemurs elect to use their 
noses to respond instead of their fingers." 

When participating in these tests, "the animals are not coerced or forced in 
any way," Brannon said. When the touch screen is wheeled into Aristides' home 
cage, he eagerly runs over and begins touching immediately to obtain sugar 
pellet rewards. 

In a second set of trials Brannon's team is testing 20 individuals of both 
lemur species to understand their abilities to count numbers in foraging 
contexts. 

One experiment tests a lemur's ability to reliably pick the larger of two 
piles of raisins. (Like many animals, lemurs get better at this the larger 
the difference between the two piles.) Brannon hopes to further this 
experiment by testing whether the precision with which lemurs make quantity 
judgments depends on differences in social structure and ecology between 
species. 

"For example," Brannon explained, "ring-tailed lemurs live in the largest 
social groups of all prosimians. If complexity of social structure is a 
pressure to develop certain aspects of intelligence, we should expect 
ring-tailed lemurs to surpass all other prosimian species on tasks that tap 
those aspects of intelligence," she said. 

Another experiment tests if the amount of time a lemur will spend searching 
in a bucket for rewards, reflects how many rewards he thinks are buried in 
the bucket. Lemurs watch Brannon and her co-workers drop a number of grapes 
into a bucket—some of which are hidden in a secret compartment. Then the 
researchers measure how long the animals spend searching for those grapes. 

Clues to Evolution of Human Brain? 

Brannon's project is "great stuff," commented Patricia Wright, a world 
authority on lemurs at the State University of New York in Stony Brook. "The 
long neglected 'dunces' of primates are showing that the test givers were 
just not asking the questions in the right way," she said. "Lemurs don't have 
the kind of hand coordination to pull and push levers, but that doesn't mean 
they don't know the correct answers." 

Working alongside her graduate student in Madagascar's Ranomafana National 
Park, Wright's own studies have recently revealed that lemurs, which range 
over wide areas and have more flexible diets and social systems, appear 
brighter than those with small ranges. 

Though Brannon's current pilot projects have focused on only two species, she 
hopes to expand her project to ask similar questions about how differences in 
lifestyle and ecology have affected intelligence in many different species of 
lemur. (The Duke University Primate Center carries out captive breeding 
programs, conservation work, and other projects with up to 300 individuals of 
25 species of prosimian primates). 

Some of the factors which have driven the development of intelligence in 
lemurs like Aristides could be the same factors that led human ancestors on 
the path to developing the sophisticated numerical and other cognitive 
abilities that we possess today. 

"We can't go back and look at intelligence in the fossil record to understand 
the thought processes of the earliest primates," Brannon said. "But we can 
try and understand what the minds of all primates share and how they differ 
from other mammals."