Does Brain Size Matter?

A Bigger Brain does not always make you smarter.

As the body size of an organism grows, so does its brain size (mostly), although, size alone does not make an animal smarter. Elephants have the largest brain volume among the terrestrial animals. The brain of an African elephant weighs a massive 11 pounds (human brain weighs only 3 pounds) and contains an astounding 250 billion neurons (human brain has about 86 billion neurons) but sheer size does not make the elephants brainier. The average IQ of these beasts of burden is only 1.88. This is an amazing 30 times less than the minimum average IQ of any human group. San Bushmen have an IQ of only 56. On the other hand, it is 60 times less than the average IQ of smartest humans on the planet – Ashkenazi Jews (average IQ 108 – 115). That means, Ashkenazi Jews have average IQ that is twice that of San Bushmen, but their brain size is not twice that of San people (average brain size (cc): San - 1270; Ashkenazis [European] - 1370). It is just a 100cc difference in brain size, which is less than 10% of total brain size, but in endows the Ashkenazim a 200% capacity than the San people. Let’s go back to the elephants now. Its not that the elephants are wallowing around just carrying an extra weight that does nothing; they have other needs.

In order to address this variance in brain size and cognitive ability, a statistic called 'Encephalisation Quotient' or EQ was proposed. According to it, as the size of body of an animal increases, the size of its brain should too, because only a bigger brain can control a bigger body. In the case of elephants, they have a skin area (20m3) which is 10 times more than that of human skin area (2m3). Their skin is so sensitive that they can feel even a fly landing on it. Possibly, its all the nerves spread around the skin – that make it so sensitive – and the corresponding neurons in the brain that are responsible for consuming a better part of brain volume. Thus, in comparison to humans, a far larger number of neurons in elephants are dedicated only to 'feel' the world around them. This may be the case, because 97.5% of neurons in elephant’s brain are found in its cerebellum , an area that controls movement, muscle contraction (for example, in skin) and balance.

But, this is not a universal finding; some birds have a lower EQ, still they are smarter than many animals with quite large brains. Capuchin monkeys have a larger EQ than chimpanzees and rhesus monkeys have a larger EQ than a gorilla, but neither is a capuchin smarter than a chimp nor a rhesus monkey smarter than a gorilla. Other people point out that even a cat has same moving body parts as that of an elephant’s, same number of limbs and similar mechanisms for locomotion, so there is no requirement of a larger brain, a cat size brain would do; to support this logic, they cite the example of brontosaurus – weighing 100 tons and 110 feet long – who had brains the size of tennis balls. They thrived for a long, long time, till an asteroid wrested the survival advantage from them. `

One crucial area of brain that is very different in elephants and humans is cerebral cortex, associated with higher cognitive functions and intelligence. There are 16 billion neurons in human cerebral cortex but only 5.6 billion in elephant’s cerebral cortex. On the basis of this, some hypothesize that it is the absolute number of neurons in the cerebral cortex that is correlated to higher intelligence.

Mankind's history on the planet offers us further clues. Once upon a time we used to have close cousins – Neanderthals and Denisovans – human species who are now extinct. DNA can be extracted and sequenced from their fossils. Researchers at UCSF, San Diego have identified a gene called NOVA1 in Neanderthals and Denisovans which is different from NOVA1 in humans. This gene is involved in forming synapses in the brain which connect one neuron with the next and a modification of its activity leads to neurological disorders.

Using latest gene editing technologies, they introduced the extinct version of gene in human stem cells and grew them in the laboratory into tissue masses almost 5mm across. They compared these tiny brain organoids with those organoids having the human version of NOVA1 and found significant differences in size, shape and textures of Neanderthal/Denisovan brain organoids; the latter had smaller, bumpier organoids. The human brain organoids were larger, spherical and smoother in comparison. Moreover, the activity of another 277 genes was found altered in the Neanderthal/Denisovan brain organoids, there were different amounts of synapse proteins with a relatively disorderly neuronal firing. How is it important to our story?

Neanderthal and Denisovans were evolutionary dead ends. They left the planet without leaving any surviving relatives. Their remains and the circumstances of their remains indicate that they were not very smart and that might have cost them their existence. But, the most astonishing fact of this story is that Neanderthals had a larger brain size than the extant humans. So, in spite of having large brains, the genes in their brains were different and this affected the resulting processing power of their brains.

Another example from history comes from another species of extinct humans. Homo floresiensis, aka the hobbits, were a species of short statured archaic humans who were on average only 3feet and 7 inch tall and there brain was only 380cm3 which is half of their (and our) ancestors – Home erectus. It is suggested that a group of large bodied Home erectus humans became stranded on the island of Flores in Indonesia about a million years ago where it underwent through the 'island rule'. The island rule proposes that small animals become larger if stranded on an island where there are no predators present while the larger animals become smaller if the food resources are limited. Although, under the island rule, those archaic humans became hobbits and their brains shrunk accordingly, the capacity of their brains did not suffer. They remained as adept at tool making as their ancestral Homo erectus with a twice larger brain and survived on the island for almost a million years.

In the end, human and elephant (or Neanderthal or Denisovan or Homo floresiensis) brains are all different in many ways. They have different architectures, the number of neurons in different parts of the brains are different, those neurons are connected in different ways and they differ in the way they process information. This makes us different from the elephants. We have the ability to systemize, we can make if-then logic circuits in our thoughts and use those thoughts, with the help of our opposable thumbs, to make and use tools and with the help of language we can transfer those thoughts (techniques) of tool-making to our fellow human beings. Elephants don't need and they don't have what it takes to be human and that is what makes the difference. Our brains suit best to us and theirs to them.