December 2010, Week 2


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Fri, 10 Dec 2010 22:32:56 -0500
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Dogs Have Bigger Brains Than Cats Because They Are More
Sociable, Research Finds


ScienceDaily (Nov. 28, 2010) -- Over millions of years
dogs have developed bigger brains than cats because
highly social species of mammals need more brain power
than solitary animals, according to a study by Oxford

For the first time researchers have attempted to chart
the evolutionary history of the brain across different
groups of mammals over 60 million years. They have
discovered that there are huge variations in how the
brains of different groups of mammals have evolved over
that time. They also suggest that there is a link
between the sociality of mammals and the size of their
brains relative to body size, according to a study
published in the PNAS journal.

The research team analysed available data on the brain
size and body size of more than 500 species of living
and fossilised mammals. It found that the brains of
monkeys grew the most over time, followed by horses,
dolphins, camels and dogs. The study shows that groups
of mammals with relatively bigger brains tend to live
in stable social groups. The brains of more solitary
mammals, such as cats, deer and rhino, grew much more
slowly during the same period.

Previous research which has looked at why certain
groups of living mammals have bigger brains has relied
on studies of distantly-related living mammals. It was
widely believed that the growth rate of the brain
relative to body size followed a general trend across
all groups of mammals. However, this study by Dr
Susanne Shultz and Professor Robin Dunbar, from Oxford
University's Institute of Cognitive and Evolutionary
Anthropology (ICEA), overturns this view. They find
that there is wide variation in patterns of brain
growth across different groups of mammals and they have
discovered that not all mammal groups have larger
brains, suggesting that social animals needed to think

Lead author Dr Susanne Shultz, a Royal Society Dorothy
Hodgkin Fellow at ICEA, said: 'This study overturns the
long-held belief that brain size has increased across
all mammals. Instead, groups of highly social species
have undergone much more rapid increases than more
solitary species. This suggests that the cooperation
and coordination needed for group living can be
challenging and over time some mammals have evolved
larger brains to be able to cope with the demands of

Co-author and Director of ICEA Professor Robin Dunbar
said: 'For the first time, it has been possible to
provide a genuine evolutionary time depth to the study
of brain evolution. It is interesting to see that even
animals that have contact with humans, like cats, have
much smaller brains than dogs and horses because of
their lack of sociality.'

The research team used available data of the
measurements of brain size and body size of each group
of living mammals and compared them with similar data
for the fossilised remains of mammals of the same
lineage. They examined the growth rates of the brain
size relative to body size to see if there were any
changes in the proportions over time. The growth rates
of each mammal group were compared with other mammal
groups to see what patterns emerged.


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