Encephalisation Quotient as a Gauge of Intelligence

mammal EQ

Science may be built on unbiased precepts, but current scientists certainly aren’t. They all share the same extreme flaw, namely that they are all human.

We humans can’t cope too well with doubt. We only settle to our comfort zone if the evidence can be forced into upholding a coherent story. The result for science is to take the textbook description as the reality. This is called the ‘paradigm approach’. The paradigm approach works well if we have a few temporary areas of doubt which we then tag for immediate investigation, but if further testing is too long in coming, the best guess of the leading expert in the field becomes enshrined as if fact and the total lack of its basis quickly forgotten. Take just one example: how many among you think that the paradigm of ‘high stomach acidity causing gastric ulcers’ was a conspiracy by drug companies?

I agree that (if we forget the human factor) conspiracy would be a logical conclusion looking back over that folly from today. The first evidence that it was actually caused by bacterial infection comes in 1896, yet it took a maverick physician continually proving he could cure those ulcers with antibiotics before the correct explanation for them was finally accepted in the 1980s. Only then did the pharmaceutical companies lose their most profitable product. I wish it were a conspiracy, but this was no more than a typical, if sad, example of the way the paradigm aproach allows error to creep into the body of our scientific knowledge.

Likewise, when scientists first came to study mammalian brains in earnest, they were struck by a problem. Bigger should be better, yet several animals had larger brains than humans. On land (where it would be particularly difficult to hide human-level behavioural complexity from our observation), that constituted the two genera of extant elephant. Elephants have a brain three times larger than our own, yet they are certainly not smarter. A couple of decades ago the consensus was that elephants were just below chimps, gorillas and orangutans in intelligence. The current consensus (after more and subtler testing) is that their intelligence is on par with the great apes.

In a few such conspicuous cases, measured intelligence diverged from that expected from brain size alone. This led to an idea in science that has never been backed by any peer reviewed evidence. It is called the encephalisation quotient, or EQ hypothesis. Quoting Wikipedia, the EQ of an animal 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.” Now the idea is that EQ is “a rough estimate of the intelligence or cognition of the animal” This has never made much sense. If we were writing computer code to operate a body, neither the length of code, nor the computer needed to operate it would have any dependence on the size of that body. That doesn’t mean though that we can’t think up models where this may be true. An example of this is if it is assumed muscle bundles have a maximum size in mammals (they don’t), and each has to be controlled directly from the brain without signal pre-processing in the spinal cord (they aren’t).

If EQ were a useful concept we could make many predictions. At minimum, one would expect it to be difficult to find a higher correlate of brain mass than body size. In reality, it is often found to be inferior at predicting raw brain mass than other variables, especially longevity. Another obvious prediction is that body-size driven growth demands, first and foremost, growth in the cerebellum yet, what we actually see, is disproportionate growth in cerebrum volume. How could we possibly maintain the EQ hypothesis given that fact? Are we to hypothesis that bigger eyes require proportionately more thinking before an animal can understand the concept of the colour ‘blue’.

Just as some were tying themselves in knots to maintain the EQ hypothesis came a killer blow. The first work that has ever been able to test the hypothesis directly was a meta-analysis of intelligence across different primate species, and it found that brain size, and brain size alone, was an important predictor of intelligence.

Even more recently, attempts have been made to find measures of intelligence that can be used across mammalian orders so that comparisons can be made. Once more, the first of these has shown that brain size is the best predictor of these measures. By comparison, when we try the same thing, this time with brain size adjusted for body size, that correlation effectively disappears. For another perspective on these findings you can look here.

Worst of all for the hypothesis, the original problem for which EQ was created, no longer exists. We now know that the brains of different mammalian orders can scale up quite differently from each other. Recent work finds the energy usage of mammalian brains tracks the number of neurons irrespective of their size. The number of neurons in the rather large cerebrum of an elephant is the same as that in the great apes. If great apes and elephants have the same cerebral energy demand, the same level of intelligence should be expected, not a surprise. Please note that within each mammalian order a larger brain always indicates a brain with more neurons, and it is only comparisons across orders that require utmost care.

So the fat lady has sung and the concept of EQ is all over, right? Not quite! We have not yet acquired the base or type of data that supports unadjusted brain size against EQ in non-primate mammals at the confidence level with which we can dismiss EQ in primates. That still allows a little wiggle room. What if brain size is only all important for primates? If primates were the anomaly, we could still call ourselves rational, yet believe that EQ is an important predictor of intelligence for other mammals until such times as we have better data for them. In that way, they can go on believing in EQ even though the hypothesis has only ever shown support in a few post hoc case examples (in science, that would normally count as having no support at all). Humans being human, most scientists currently tick that option.

cetacean EQ

Sperm whales possess the largest brains on Earth today. Though the fossil record of cetaceans is less complete than most mammals, many scientists pick them as having the largest brains our planet has ever produced,. We dismiss that fact as trivia at our peril.

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