From The Sunday Times
January 3, 2010
Dolphins have long been
recognised as among the most intelligent of animals but many researchers had
placed them below chimps
Dolphins have been declared the world’s second most intelligent creatures
after humans, with scientists suggesting they are so bright that they should be
treated as “non-human persons”.
Studies into dolphin behaviour have
highlighted how similar their communications are to those of humans and that
they are brighter than chimpanzees. These have been backed up by anatomical
research showing that dolphin brains have many key features associated with high
The researchers argue that their work shows it is morally
unacceptable to keep such intelligent animals in amusement parks or to kill them
for food or by accident when fishing. Some 300,000 whales, dolphins and
porpoises die in this way each year.
“Many dolphin brains are larger than our
own and second in mass only to the human brain when corrected for body size,”
said Lori Marino, a zoologist at Emory University in Atlanta, Georgia, who has
used magnetic resonance imaging scans to map the brains of dolphin species and
compare them with those of primates.
“The neuroanatomy suggests psychological continuity between humans and dolphins
and has profound implications for the ethics of human-dolphin interactions,” she
Dolphins have long been recognised as among the most intelligent of
animals but many researchers had placed them below chimps, which some studies
have found can reach the intelligence levels of three-year-old children.
Recently, however, a series of behavioural studies has suggested that dolphins,
especially species such as the bottlenose, could be the brighter of the two. The
studies show how dolphins have distinct personalities, a strong sense of self
and can think about the future.
It has also become clear that they are
“cultural” animals, meaning that new types of behaviour can quickly be picked up
by one dolphin from another.
In one study, Diana Reiss, professor of
psychology at Hunter College, City University of New York, showed that
bottlenose dolphins could recognise themselves in a mirror and use it to inspect
various parts of their bodies, an ability that had been thought limited to
humans and great apes.
In another, she found that captive animals also had
the ability to learn a rudimentary symbol-based language.
Other research has
shown dolphins can solve difficult problems, while those living in the wild
co-operate in ways that imply complex social structures and a high level of
In one recent case, a dolphin rescued from the wild
was taught to tail-walk while recuperating for three weeks in a dolphinarium in
After she was released, scientists were astonished to see the
trick spreading among wild dolphins who had learnt it from the former captive.
There are many similar examples, such as the way dolphins living off Western
Australia learnt to hold sponges over their snouts to protect themselves when
searching for spiny fish on the ocean floor.
Such observations, along with
others showing, for example, how dolphins could co-operate with military
precision to round up shoals of fish to eat, have prompted questions about the
brain structures that must underlie them.
Size is only one factor.
Researchers have found that brain size varies hugely from around 7oz for smaller
cetacean species such as the Ganges River dolphin to more than 19lb for sperm
whales, whose brains are the largest on the planet. Human brains, by contrast,
range from 2lb-4lb, while a chimp’s brain is about 12oz.
When it comes to
intelligence, however, brain size is less important than its size relative to
What Marino and her colleagues found was that the cerebral cortex
and neocortex of bottlenose dolphins were so large that “the anatomical ratios
that assess cognitive capacity place it second only to the human brain”. They
also found that the brain cortex of dolphins such as the bottlenose had the same
convoluted folds that are strongly linked with human intelligence.
increase the volume of the cortex and the ability of brain cells to interconnect
with each other. “Despite evolving along a different neuroanatomical trajectory
to humans, cetacean brains have several features that are correlated with
complex intelligence,” Marino said.
Marino and Reiss will present their
findings at a conference in San Diego, California, next month, concluding that
the new evidence about dolphin intelligence makes it morally repugnant to
Thomas White, professor of ethics at Loyola Marymount
University, Los Angeles, who has written a series of academic studies suggesting
dolphins should have rights, will speak at the same conference.
scientific research . . . suggests that dolphins are ‘non-human persons’ who
qualify for moral standing as individuals,” he said.