THEY were touted as the brain cells that set humans and the other great apes apart from all other mammals. Now spindle neurons 鈥� the specialised brain cells thought to process our emotions and that may even enable us to love and suffer 鈥� have been found in whales. The discovery will stimulate debate both on the level of whale intelligence and on the ethics of hunting them.
Spindle cells, named for their long, spindle-shaped bodies, occur in the parts of the human brain linked with social organisation, empathy, speech, intuition about the feelings of others and rapid 鈥済ut鈥� reactions (see New 杏吧原创, 19 June 2004, p 32). It turns out that they are in the same place in the brains of humpback whales, fin whales, killer whales and sperm whales. What鈥檚 more, they have existed in whales for at least twice as long as we have had them, and early estimates suggest they could have three times as many as us proportionately.
鈥淚t鈥檚 absolutely clear to me that these are extremely intelligent animals,鈥� says Patrick Hof of the Mount Sinai School of Medicine in New York, who found the whale spindle cells with colleague Estel Van Der Gucht. 鈥淲e must be careful about anthropomorphic interpretation of intelligence in whales,鈥� he adds, 鈥渂ut their potential for high-level brain function, clearly demonstrated already at the behavioural level, is confirmed by the existence of neuronal types once thought unique to humans and our closest relatives.鈥�
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Dolphins seem to be capable of self-recognition (New 杏吧原创, 4 November 2006, p 17) and Hof suspects humpback whales are too. 鈥淭hey communicate through huge song repertoires, recognise their own songs and make up new ones. They also form coalitions to plan hunting strategies, teach these to younger individuals, and have evolved social networks similar to those of apes and humans,鈥� he says.
Like all other species with spindle cells, whales undergo an unusually long period of development before sexual maturity, they have very few offspring at one time, and adults can live independently from other whales for long periods.
Hof and Van Der Gucht found the spindle cells in two regions vital for 鈥渧isceral鈥� reactions 鈥� those that require fast but emotionally sensitive judgements, such as whether another individual is suffering pain and the general feel of whether an experience is pleasant or unpleasant (The Anatomical Record Part A, DOI: 10.1002/ar.a.20407).
鈥淲hales have spindle cells in regions vital for reactions that require fast but emotionally sensitive judgements鈥�
One area, the anterior cingulate cortex, lies beneath the midline at the front of all mammalian brains (see Diagram). In humans it guides attention, senses pain and registers mistakes. By tapping into body systems that control breathing, heart rate, erections and other automatic responses, it helps us to register emotions such as fear, disgust, anxiety and intense pleasure or pain.
The other region is the frontoinsular cortex, reckoned to be critical for emotional responses to others, such as when someone else is suffering, or a baby cries. It also helps us spot attempts at deception.
In whales, spindle cells were also found in another region, the frontopolar cortex, and were sparsely distributed elsewhere, though Hof says he doesn鈥檛 yet know the significance of spindles in these areas.
The shape of the spindle cells may provide a clue to their function. 鈥淭hey鈥檙e like the 鈥榚xpress trains鈥� of the nervous system,鈥� says Hof. Their long length enables them to fast-track information around the cortex, bypassing irrelevant connections, enabling us to instantly process and act on emotional cues during complex social interactions.
鈥淢y interpretation is that the spindles are adaptations which support fast communication of information from the anterior cingulate cortex and the frontoinsular cortex in very large brains,鈥� says neuroscientist John Allman, a spindle cell researcher at the California Institute of Technology in Pasadena.
Spindle neurons transmit highly processed information, says Hof, which helps us formulate behavioural responses. This might include responding verbally, retrieving memories and images, empathy, feelings and insight. It鈥檚 tantalising to think that the songs and vocalisations of whales might be based on similar processing.
鈥淭he discovery is a stunning example of neuroanatomical convergence between cetaceans and primates,鈥� says Lori Marino of Emory University in Atlanta, Georgia. 鈥淭his is consistent with a growing body of evidence for parallels between cetaceans and primates in cognitive abilities, behaviour and social ecology.鈥�
The brains of smaller cetaceans examined by Hof and Van Der Gucht didn鈥檛 have spindle cells. The only toothed whales 鈥� the suborder of cetaceans that includes dolphins 鈥� to have spindles were the two largest, the killer whale and the sperm whale. But Hof suspects that all baleen whales, such as humpbacks and fins, are likely to have the cells.
The smaller cetaceans might have evolved some kind of alternative to spindle neurons. 鈥淚n this respect, it will be interesting to discover what mental capacities might distinguish humpback whales from dolphins,鈥� says Keith Kendrick, a neuroscientist at the Babraham Institute in Cambridge, UK.
Kendrick also warns against assuming that the spindle cells must be linked with complex socialisation, which is one explanation put forward for the evolution of increased brain size. 鈥淎t this point, we don鈥檛 know for sure what the key functions of these spindle cells are, and whether they really do represent an important index of higher social and intellectual functioning,鈥� he says.
Hof is convinced, however, that the cells signify intelligence. 鈥淲hales have evolved absolutely unique traits in their environment,鈥� he says. 鈥淭hey don鈥檛 have written language but they can do a lot, and their fishing strategies are better than ours.鈥�
All the more reason, he says, for rethinking whaling strategies on humanitarian grounds. 鈥淭hat such a parallel trait occurs in such divergent groups of animals as primates and cetaceans speaks to the need to protect them and understand fully their biology and ecology.鈥�
Inside the mind of a Whale
One of the greatest problems facing researchers interested in whale intelligence is a logistical one. It鈥檚 just not easy to carry out the kind of intense behavioural observations needed, like Jane Goodall鈥檚 observations of chimpanzees in the wild. For this reason, our understanding of whales falls well short of that of the great apes.
鈥淲e鈥檙e several decades out of kilter,鈥� says Mark Simmonds of the Whale and Dolphin Conservation Society in Chippenham, UK. Despite the relative lack of information, Simmonds has reviewed a wealth of evidence for apparent emotional and intelligent behaviour in cetaceans (Applied Animal Behaviour Science, vol 100, p 103).
In 1990, for example, two male orcas were observed swimming together without any contact with other orcas for several days, after the body of their mother was found floating dead nearby. They appeared to be retracing their mother鈥檚 last movements, which researchers tookto be a sign of grief.
Does this mean we should treat them better? Around 200,000 cetaceans are killed annually in fishing nets, and Japanese whaling statistics suggest that just 40 per cent of hunted animals die instantaneously.
鈥淚t is clear deaths in hunts and fishing nets may often be prolonged and painful and also significantly affect more members of the population than just the animals killed,鈥� says Simmonds. 鈥淢eanwhile, if cetaceans are passing information from generation to generation, and you then start to wipe out some of the cultural populations, other populations may not be able to occupy the niches left behind. Should we be focusing on conserving the species, particular groups in oceans, or the cultural groups that they鈥檙e divided into?鈥�
Linda Geddes
