This has always been one of the most puzzling questions related to dolphin drive hunts, like Taiji, and the wild orca captures of the 1960s, 70s, and 80s (that are featured in Blackfish). Dolphins (and orcas are large dolphins) do not attack humans–even though they easily could–that are slaughtering them or taking their calves. It is hard to imagine almost any other species, reacting with the same passiveness or pacifism. Imagine trying to kill or take the cubs from a bear or a lion.
I’ve occasionally asked this question of dolphin experts like Lori Marino, but there is no obvious or satisfactory answer. Here, Laura Bridgman takes a shot and digs into the science that might suggest some answers to this profoundly complex question:
Our brains share many structural similarities with dolphins. For example, we both have a limbic system, which is responsible for handling emotional information. One difference between us, however, is that the dolphins’ limbic system is much larger than ours and, says scientist Denise Herzing, it “may be stretched out over more of the brain,” indicating that “the dolphin brain may have more of a ‘global connection’ to [emotional] information”. This could mean that dolphins are more emotional than humans, and that emotions could figure more prominently throughout their thought processes.
While it might be tempting to think that increased emotions would lead to greater aggression when being backed into a corner, another compelling feature of the dolphin brain appears to account for this notion. Sterling Bunnell, in The Evolution of Cetacean Intelligence points out that the cerebral cortex, responsible for logical thought and reasoning in both humans and dolphins alike, is controlled by the emotional activity of the limbic system. This process is facilitated by what are called ‘neocortical association neurons’.
Bunnell observed that, in human studies, the ratio of these neurons to limbic-system brain stem neurons “is necessary for such qualities as …emotional self-control” and that a decreased ratio is associated with “impulsiveness, emotional instability, irritability, loss of humor”. Bunnell points out that dolphins possess a higher neocortical-limbic ratio than the average human, suggesting that their control over their own emotions is greater than what we experience.
It could be that dolphins, while being more emotional, are more emotionally stable than we are, and are therefore able to better control themselves in stressful situations. This could explain their apparent control over the impulse to lash out at the humans who are so callously ending their lives.
This is an interesting hypothesis, but it makes me wonder what the evolutionary advantage or benefit of controlling emotions might be when experiencing an existential threat. In other words, in these situations it would be to the dolphins advantage NOT to control emotion and remain passive.
Whatever the answer, I suspect that if and when we do come to understand why dolphins behave with such pacificism when under attack by humans the answer will humble us.