Are Dolphins Dimbulbs?
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.
7 thoughts on “Are Dolphins Dimbulbs?”
[quote]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.[/quote]
[quote] 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.[/quote]
phht. He didn’t spend much time looking at the literature on vocal communication in mammals, did he?
heck, hyenas have dozens of categories of communication types, and they don’t even use echolocation. Steve Glickman’s lab up in Berzerkeley was doing a lot of work on that.
Manger’s articlej ust sounds like a hack job to produce a quick article with meaningless conclusions to me.
er… Manger mangled it.
then of course, if Manger considers brain size related to biosonar processing in dolphins, you’d think he might look at whether similar patterns occur in other echolocating mammals.
or heck, like i said over on ATBC, why not compare to an entirely different system that is just as specialized, like electrolocation in knifefishes?
odontocete vocalizations are primarily produced at the phonic lips, not the “vocal cords”.
AFAIK, odontocetes don’t have vocal chords at all.
you can make an even stronger statement than the one you made.
Nice analysis, Wesley. I’d point out that Manger has another problem: a recent study that suggests bottlenose dolphins have sound-based names. See http://dsc.discovery.com/news/briefs/20060508/dolphin_ani.html. Even if the names are simple and often repeated among individuals, the giving of individual names requires the concept of individuality, which itself suggests high intelligence.
Ichthyic: Still waiting on the return call. I’ll let you know when I get it. I do have some correspondence going with Sam Ridgway about this; I’ll see whether he’s interested in making a response. Ridgway says that he has argued with Manger before.
Wolfwalker: The signature whistle hypothesis research is interesting, but I’m wondering why people get so excited about looking solely at signals that are only a small fraction of the complete repertoire that are produced? Until recently, most whistle work was based on recordings that topped out at the upper limit of available audio recording gear, somewhere in the 16 to 20 kHz frequency range. Bottlenose dolphins produce clicks with peak frequencies upwards of 150 kHz and significant energy out to about 400 kHz (about 20dB down from peak). I’ve tried to get various funding agencies interested in work to put the recording and analysis of click-based sounds on an easier to accomplish, more standardized basis without success.
I’ve presented some findings from biosonar work that indicates the use of individual strategies in selecting the particular way in which biosonar vocalizations are employed.
I’d have to dispute the claim Manger makes that sound production in dolphins is not under voluntary control, too. Our entire biosonar experimentation and hearing studies were premised upon the dolphins making an audible response to certain stimuli, something that should not have been trainable by operant conditioning if the response was not under voluntary control.
I’d have to dispute the claim Manger makes that sound production in dolphins is not under voluntary control, too.
Yes, I too do not understand how one can completely discount observational data in favor of morphological data.
birds too, have reduced limbic systems, but are certainly trainable and quite able to voluntarily control their vocalizations, as any parrot enthusiast could tell ya.
I feel like I’m missing something though. Surely it really isn’t as simple as Manger overlooking the incredibly obvious, is it?
do you have a link to Manger’s full article?
Sorry, I don’t have a link to a public online version of the full article. Here is the bibliographic data, though, if you have a library affiliation:
MANGER, PAUL R. BIOLOGICAL REVIEWS 81(2):293-338. 2006.
An examination of cetacean brain structure with a novel hypothesis correlating thermogenesis to the evolution of a big brain.
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