Heroes of the Ocean: Why do Humpbacks exhibit altruism?

Exploring the selfless behaviour of humpback whales and its potential neurological and evolutionary implications.

Introduction

In ecology, altruism refers to behaviour that benefits the receiver at a cost to the donor. Many species have been observed to display altruistic behaviours, in particular the humpback whale (Megaptera novaeangliae). These highly intelligent mammals exhibit a unique altruistic practice called ‘mobbing’ (Lorenz, 1963) whereby adult humpbacks launch an ambush on attacking orcas (Orcinus orca) risking injury to protect vulnerable calves and a variety of marine species.

Mobbing is just one of many complex social behaviours illustrating the remarkable cognitive capacity of humpbacks. Other examples include vocalisations, matriarchal grouping, and cooperative hunting using ‘bubble-nets’ (Wiley et al., 2011). Understanding the drives of humpback social behaviour can provide valuable scientific insight with useful applications. For instance, studies of their cooperative hunting techniques have inspired the Whale Optimization Algorithm (WOA) (Mirjalili + Lewis, 2016), a mathematical model that mimics ‘bubble-net’ hunting to solve complex optimization problems. Such research reveals how exploring the complexities of social behaviour has potential for technological innovation.

Cetaceans diverged from terrestrial mammals ~50 mya (Graur + Higgins, 1994), while baleen whales (Mysticeti) - including humpbacks - branched from toothed whales (Odontoceti) ~39 mya. Research into the neuroanatomy and intelligence of humpbacks remains relatively recent compared to Odontoceti. Emerging research has begun to shed light on their exceptional intellect, providing indication for their selfless behaviour and underlying neurological adaptations

Evidence

Researchers (Hof + Van Der Gut, 2007) examined the cerebral cortices of a humpback, several Odontoceti and the fin whale (Balaenoptera physalus). This revealed significant findings, including the presence of spindle neurons in humpback brains. These specialised cells were previously considered exclusive to humans, playing roles in conscious awareness and emotional processing (Brüne et al., 2011; Fuentealba-Villarroel et al., 2022). Spindle neurons were abundant in layer V of the anterior insula and anterior cingulate cortex of just 2 Ondoncetes (sperm and killer whales), the fin whale, and the humpback whale. Density of these cells was higher in the Frontopolar cortices of the humpback compared to Ondoncetes. This region is associated with processing and manipulating complex information (Kroger + Kim, 2022), suggesting the unique capacity of humpbacks to make conscious judgments. The humpback also displayed dense neural clusters in the inferotemporal and occipital neocortex, regions associated with sophisticated visual processing and recognition of complex objects (Osaka et al., 2009, pp.187–203). Damage to the inferotemporal neocortex in humans can result in ‘facial blindness’ (Etcoff et al., 1991), demonstrating its role in social recognition. Thus, high development of these cortical regions may encourage the social behaviours exhibited by humpbacks, including communication patterns and coordinated group activities such as mobbing.

A meta-analysis reported 115 observations of humpback mobbing behaviours in response to orcas that were usually of a mammal-eating variety (Pitman et al., 2016). In >87% of situations where humpbacks initiated interactions, orcas were attacking prey at the time, indicating a proactive intention to interfere with attacks. Interestingly, only 11% of orca prey were humpbacks; 89% comprised 10 other species including 3 cetaceans, 6 pinnipeds, and 1 teleost fish. The tendency to harass attacking orcas regardless of the prey species implies the possibility of interspecific altruism (Hof + Van Der Gut, 2007).

Discussion

Pitman’s meta-analysis provides valuable ethological data, revealing the unique mechanisms of humpback mobbing. However the lack of experimental control raises concern. Observers may misinterpret or indirectly interfere with behaviour, leading to biased outcomes. Therefore it remains uncertain whether results are interspecific altruism or unintentional. Future research would benefit from instead utilising non-invasive camera methods to record data such as DTAGs — tracking devices used to reliably observe humpback ‘bubble-net’ feeding behaviours (Schmidt et al., 2010).

Furthermore, there are issues regarding the extrapolation of neurological findings from humans to cetaceans. Indeed, the inferotemporal neocortex may enable facial recognition in humans (Etcoff et al., 1991), but how do we know it provides the same purpose in humpbacks? (Hof + Van Der Gut, 2007) argue the very existence of specialised spindle neurons in the brains of both humpbacks and humans, similar in structure and distribution, suggests they evolved in parallel. This supports functional extrapolation due to similar cortical evolution.

To understand why humpbacks exhibit altruism, we must understand how it evolved. Altruism towards pod members can be explained by kin selection (Smith, 1964), which proposes traits that increase individual fitness (i.e. the reproductive success of their offspring) are positively selected for. Thus, putting oneself in danger (e.g. to protect a relative) would help pass on shared ‘altruistic’ genes. Kin selection appropriately explains the benefits of mobbing behaviours in response to an orca attack targeting another humpback.

Still, this explanation is not viable in situations where the victim is of another species. (Pitman et al., 2016) reveals that humpback altruism may extend beyond kin selection. It is entirely plausible that humpback brains are programmed to respond to orca attacks regardless of the species, strongly supported by their aptitude in pattern recognition. But until this is empirically tested, interspecific altruism cannot be ruled out.

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