Paul Manger has found a fast-track to academic notoriety: say something controversial about dolphin intelligence. Specifically, Manger contends that dolphin brain size and constituent cell type is consistent with rapid size increase to adapt to a cold marine environment, and is inconsistent with brain size increase for increasing intelligence.
Manger’s paper lays out two lines of evidence for high intelligence of cetaceans: encephalization quotient and complexity of vocalization repertoire. The first doesn’t necessarily have to do with increasing intelligence, says Manger; an alternative selective gradient can produce the same. As for the second, Manger pretty much dismisses vocalization repertoires as not being out of the ordinary for non-human animals, and thus not indicative of high intelligence. Confident that he has dispatched the case for high cetacean intelligence, Manger goes on to his neuroanatomical review.
Of particular interest to me was this paragraph from Manger’s paper:
The neuronal control of vocalisation in various mammalian species has been extensively studied, and the neural circuitry that underlies vocalisation can be described (reviewed by Ju¨rgens, 1998). Neurons from the anterior cingulate cortex project to four locations : the medial nucleus of the amygdala, the hypothalamus, the midline dorsal thalamus and the lateral periaqueductal grey matter. The amygdala, hypothalamus, and dorsal thalamus in turn project to the periaqueductal grey matter. The periaqueductal grey matter then projects to the nucleus ambiguus and nucleus retroambiguus, which constitute the phonatory motoneurons and premotoneurons controlling the vocal cords and respiratory muscles. Two interesting features of the mammalian vocal control system of relevance to the cetaceans are : (1) the majority of the vocal control system of the telencephalon belongs to the limbic system; and (2) all telencephalic control of vocalisation is channeled to the brainstem through the periaqueductal grey matter.
If Manger is basing his views of odontocete neuroanatomy as it relates to vocalization as it apparently controls the “vocal cords”, then essentially anything he says about that neural control can be summarily discarded as irrelevant: odontocete vocalizations are primarily produced at the phonic lips, not the “vocal cords”. For example:
Previous studies have shown that the anterior cingulate cortex of monkeys is important in the voluntary control of vocalisations (Sutton, Larson & Lindeman, 1974). Thus, as the cetacean limbic system is reduced, and the anterior cingulate cortex is both reduced and lacks a granular region, it is not unlikely that the voluntary control of vocalisation by cetaceans suffers serious deficiencies. However, as the amygdala appears normal, we can also conclude that involuntary species-specific intonations provided to vocalisations by this structure (Ju¨rgens, 1998) are present.
The first conclusion critically depends upon the mechanism of sound production being the same in both monkeys and dolphins. It isn’t, and the conclusion doesn’t follow. For a review paper, this strikes me as particularly inept on Manger’s part.
I’m hoping to have a chat with a colleague who is a marine mammal anatomist later this afternoon. I’ll let you know whether I’m on track here or have a helping of crow for dinner.
The link to antievolution argumentation lies in the shallowness of Manger’s approach, and the corresponding shallowness seen in antievolution argument. There are more lines of evidence for cetacean intelligence than Manger reviews, yet he acts as if he has accounted for all the relevant data in his dismissal. This is a common tactic among antievolutionists as well.
As an example of the shallowness I referred to, Manger discusses the repertoire of whistle vocalizations in bottlenose dolphins. Having found a handful of references that state that these can be categorized in less than ten types, Manger rests his case that nothing outside the non-human animal norm is to be seen here. Manger completely overlooks the fact that bottlenose dolphins produce another, entirely different, repertoire of vocalizations, those that are based upon click trains. In fact, most of the words used to describe dolphin vocalizations actually describe click train-based calls, not whistles. The scientific literature has rather a lot of information on one particular subset of click-based vocalizations in dolphins: those used for biosonar. It has rather less about click-based vocalizations used for intraspecific communication. Manger does not note the existence of these vocalizations for the purpose of his review of neural control of repertoire. Manger does take up the case of whether the dolphin’s brian needed to be larger to process received biosonar signals, which makes it all the more curious as to why he failed to consider their production.