Dolphins' Big Social Brains Linked to Attention to the Dead

A study of postmortem attentive behavior showed females do it more than males.

Posted May 24, 2018

Very little is known about how nonhuman animals (animals) respond to the presence of dead conspecifics, members of the same species. However, researchers working in the growing field of "comparative thanatology" are paying much more attention to the ways in which animals respond "behaviourally, physiologically and psychologically to dead conspecifics, and the processes behind such responses." I was slightly surprised by how little we actually know given how many studies and stories there are concerning the ways in which different animals respond to the dead by grieving and mourning. However, not much is known about cetaceans (whales, dolphins, and porpoises), and this is why a recent paper by Italian biologist Giovanni Bearzi and his colleagues called "Whale and dolphin behavioural responses to dead conspecifics" caught my eye. This essay isn't available for free online so here's a summary of their findings from what is available and from my reading of the entire piece.

Dr. Bearzi and his team studied "postmortem attentive behaviour" (PAB) by analyzing available literature. The phrase "postmortem attentive behaviour" is a neutral one that doesn't suggest any motivation for the attention that was paid to dead conspecifics. They looked at 78 records and they discovered that "odontocetes (toothed cetaceans) were much more likely than mysticetes (baleen whales) to attend to dead conspecifics. Dolphins (Delphinidae) had the greatest occurrence of attentive behaviour (92.3% of all records)." Most of the observations (75%) of PAB involved females with dead calves or juveniles who might have been their own children, with the other observations (25.0%) were of males "either showing sexual interest in a dead adult or subadult, or carrying a dead calf in the presence of females." The researchers concluded that the response of females might have been attempts to rescue the young or grief. 

The "social brain" hypothesis and cognitive complexity

​I was very interested to read that encephalization, "An evolutionary increase in the complexity or relative size of the brain, involving a shift of function from non-cortical parts of the brain to the cortex," might be an important predictor of PAB. As a measure of encephalization, the researchers studied the encephalization quotient (EQ) of different species. The EQ is "a measure of relative brain size defined as the ratio between actual brain mass and predicted brain mass for an animal of a given size" (for more discussion of the EQ and relative brain size, please see "The Birds and the Bees and Their Brains: Size Doesn't Matter and "Bird Brains: Size Doesn't Matter But Number of Neurons Does"). Information on EQ's for whales and dolphins can be seen here.

What this means is that individuals of species with larger EQ's were more likely to show postmortem attentive behavior. In the research essay Dr. Bearzi and his colleagues write [references are from their essay], "Sociality in mammals is closely associated with encephalisation (Jerison, 1973). The 'social brain' hypothesis holds that 'excess brain mass', beyond that needed to run the body machinery, has evolved not only in response to environmental challenges but also to the complexity of social life (Dunbar, 1998; Shultz and Dunbar, 2010). Connor (2007) argued that in odontocete cetaceans, as well as in primates and elephants strong selective pressure towards a large brain resulted from cognitive demands imposed by mutual dependence within a network of associates, and the benefits of developing complex social skills. Consistent with that argument, Fox et al. (2017) suggested that cetacean encephalisation is predicted by social organisation, brain size being indicative of the breadth of social and cultural behaviour across cetacean species." For those wanting to know more, an excellent review of the relationship between brains and cognition in cetaceans can be found in an essay by Dr. Lori Marino and her colleagues called "Cetaceans Have Complex Brains for Complex Cognition" that is available online, and more information can be found here

Do cetaceans grieve and what do they know about death? Life in the gray zone

Whether or not cetacean PAs realise the finality of death, mammals as evolutionarily distant from Homo sapiens as cetaceans seem to share behavioural traits that include a strong, sometimes fairly long-lasting attachment to dead conspecifics.

In addition to looking at neural correlates of postmortem attentive behavior, in a section of their essay called "The debate on animal grieving," the researchers also consider the question of whether or not the observed behavior patterns could be expressions of grieving. Some individuals may have trouble "letting go" because they're so closely attached to the dead animal or don't recognize or accept that they're dead. While grieving has been observed in a number of other species, they're not sure whether descriptions of postmortem attentive behavior in cetaceans actually are expressions or grieving or bereavement. While they don't rule out this possibility, they also discuss in a section called "Do cetaceans recognise or comprehend death?" what cetaceans' concept of death might look like if they have one at all. The researchers also don't rule out that postmortem attentive behavior might also be related to finding food, but there aren't many data to support this suggestion.

Of course, the same question about what do animals truly know about death can be asked of other species in which grieving has been observed. In an essay called "Do Animals Really Know They're Gonna Die?" which I wrote concerning whether or not animals can commit suicide, I discussed this topic and wrote, "I don't know, and I'm not sure anyone else does either. This does not mean they don't, but I don't know of any research that conclusively shows they do." When I've talked to a few people about these possibilities during the past few years, I find myself resisting answering these sorts of questions with a definite "yes" or a definite "no." Living in that troubling gray zone of uncertainty—maybe they do and maybe they don't—makes me keep an open mind about the cognitive and emotional capacities nonhumans have that may inform themselves about their own demise and what they know about when others have died and aren't coming back. It also keeps me up at night sometimes wondering just who other animals are and what they really know about a lot of other things that happen in their fascinating lives.

When someone really pushes me and wants more definitive answers, I find myself answering: "I don't think that any nonhuman animal ponders that they have a finite life like humans do." But I immediately qualify that statement by clearly saying: "I really don't know and I don't think anyone else does at this time." And, I also don't think that any nonhuman knows another individual is gone forever, that their lives are over, but the key word here is think. All in all, it remains unclear just what the animals know about the concept of death. 

So, are humans exceptional among mammals and other nonhumans in having a more developed concept of their own and others' deaths? If pushed, I think they just may be, but once again, the keywords are may be. While I know that many nonhumans grieve and mourn the loss of other individuals, I also don't know that they know that the deceased are gone forever. What other animals are thinking and feeling when they're deeply saddened when another animal dies isn't clear, but it's obvious that a wide variety of animals suffer the loss of family and friends.

Where to from here?

I found this research essay on cetaceans to be fascinating reading and the researchers' discussion of postmortem attentive behavior and other aspects of cetacean behavior to be incredibly important. Their consideration of different hypotheses to explain postmortem attentive behavior is thoughtful and detailed, and their paper alone could form the basis for entire courses on animal cognition and animal emotions. They conclude, "Our current understanding is challenged by small sample size, incomplete descriptions, and lack of information on the physiology and neural processes underpinning the observed behaviour. We provide research recommendations that would improve such understanding."

They are right on the mark, in that their essay raises numerous interesting and important questions and much more research is needed to provide more definite answers to these queries. I hope that the full research paper will become available online as soon as possible. In the meanwhile, it's fascinating and challenging to entertain questions about what nonhumans know about death because they allow for broad and deep thinking about who "they" (other animals) are, who we are, and what we know about all sorts of observable behavior patterns. Perhaps non-invasive brain imaging studies will help us along as they have with our canine companions

Please stay tuned for more discussions about the cognitive and emotional lives of other animals. There's still so much to learn, and, it's clear from a good deal of detailed comparative research on other animals, we surely are not alone and are not exceptional in having evolved many highly sophisticated cognitive skills and complex emotions.

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