Brain size vs. structure as a measure of intelligence
That homo sapiens should be more intelligent than tursiops truncatus (the common bottlenose dolphin) is not immediately obvious from this image.
We’ve known for a long time that dolphins, with their very large brains, are indeed highly intelligent. But it’s not only size but also brain structure that suggests that this should be so.
Size matters of course, but it isn’t everything. Bird’s brains are relatively small, yet some species demonstrate a surprising level intelligence. African gray parrots are easily among the smartest animals on Earth, for example. Sheep and sheepdogs have brains that don’t vary much size-wise, yet the capabilities of these respective species are in no way equivalent. Elephants, sperm whales and bottlenose dolphins all have larger brains than humans do. And so on.
Brain researchers like to use something called the Encephalisation Quotient (EQ). This is the ratio of brain to body mass, and it seems to tell part of the story. The larger your brain relative to your body’s entire mass, the smarter you’re likely to be. But that’s going to be more of a rough guide than any true indicator of a specie’s intelligence. Exceptions are likely to be the rule.
It’s perhaps with brain structure that we get the most interesting insights. And even here, we’ve learned that very dissimilar structures can sometimes lead to higher-level intelligence. Think of it as a very different evolutionary pathway to the same result. For example, the octopus, while having the largest brain of any invertebrate, also reaps the benefits of a very unique arrangement of its brain physiology. This results in an impressive ability to plan and solve problems – not something we’d expected in an animal so distant from ourselves on the tree of life.
With whales and dolphins, a notable piece of evidence that’s emerged in recent years is the existence of spindle cells. We’d thought that that these could be found only in the brains of humans, along with a handful of our closest relatives (i.e. the great apes). This turns out to not be the case. Spindle cells, which are thought to make possible ‘rapid intuitive choice in complex social situations’ and are associated with a capacity for empathy, have been shown to be present in the brains of a number of cetacean species. Those identified so far include: belugas, bottlenose dolphins, fin whales, humpback whales, orcas, Risso’s dolphins, and sperm whales. Elephants also have them.
At this point, we’re already sitting on a large body of empirical data that shows these species – dolphins in particular – as capable of complex behavior and learning, transmission of knowledge between generations, and even culture. We even have reason to speculate that they may have reached a level of “social-emotional sophistication’ that exceeds our own. Let’s also remember that bottlenose dolphins have been shown to be able to recognise themselves in a mirror at ages earlier than generally reported for human children (and much earlier than our closest primate cousins).
When it comes to the question of who’s smarter, us or them, the point is probably moot, and in any event may be unanswerable for the foreseeable future. The reason for this is the fundamentally different evolutionary path that must be followed in an aquatic environment as opposed to a terrestrial one. For example, the latter would favor tool making abilities, in a way that the former would not. As a result, the specific cognitive skills required to thrive would differ considerably. How the structures and functional areas of the cerebral cortex will be organized reflects what’s needed to survive in that environment.
Dr. Lori Marino, a leading researcher into whale and dolphin brain physiology, describes this as evolution ‘along a different neuroanatomical trajectory’. In other words, evolution can provide alternative routes to complex intelligence – something our friend the octopus should have already demonstrated. Cetaceans too.
So, given that any human vs. cetacean comparison is really just a great example of evolutionary convergence, we need to think about how we ought to interact with this ‘alien intelligence’. It’s only in recent decades that our moral frontier has been extended enough to start to take them into account. Yet the striking similarities between us and them would make it a reasonable assumption that they can be vulnerable to social and emotional stresses, just as we are. That they can suffer and experience loss. This knowledge should guide our actions, and require us to do them no harm.
For The Orca’s Voice,
Your Canadian Cetacean Alliance Team
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