Are human brains unique?

The point is that any human activity can be seemingly atomized.
But to be swooned by such a fact is to miss the point of human experience.
Michael Gazzaniga

Last time, I reported on Stanislas Dehaene’s speculation that we have higher-order consciousness because the brain evolved a dynamic interactivity that goes far beyond the this-part-does-that structure of other mammal brains.

One top-shelf neuroscientist with complementary views is Michael Gazzaniga, who declared in Human: The Science Behind What Makes Your Brain Unique that our rush to identify cognitive equivalancies in other species is understandable but may be misdirected.

The human mind is so generative and given to animation that we do things such as map agency on to almost anything, our pets, our old shoes, our cars, our world. It is as if we don’t want to be alone up here at the top of the cognitive chain, the smartest things on earth. We want to see our dogs charm us, appeal to our emotions, imagine they too can suffer and have pity, love and hate and all the rest. We are a big deal and we are a little scared about it.

In “Are Human Brains Unique?” — an EDGE excerpt from Human — Gazzaniga argues that “although we are made up of the same chemicals, with the same physiological reactions, we are very different from other animals.” He notes that substances with the same chemical components, like an iceberg and a foggy mist, can have very different properties. In a similar way, he writes, “I think it is rather empty to argue that because, say, social behavior exists in humans and in ants, there is nothing unique about human social behavior.”

And while Gazzaniga engages in brain imaging research himself, he cautions that there are important limitations to a descriptive approach to brain science. Addressing the question that Dehaene ignores, Gazzaniga writes that “Although we have sophisticated imaging techniques available to us that can show us what part of the brain is involved with specific types of thoughts or actions, these scans tell us nothing of what is going on in that part of the brain.”

Gazzaniga writes that “there is not much difference between species in the genes that do routine ‘house-keeping’ in the nervous system, which are those that are involved in the most basic cellular functions such as metabolism and protein synthesis.” However, he notes, there are major differences in some of the key genes associated with higher-order cognition. And there are intriguing connections between the evolution of these “accelerated” genes and key points in human cultural development, suggesting that this kind of differentiation explains the “explosion” of higher human consciousness, a spurt that left all of the other primates behind.

Two genes that Gazzaniga highlights, both involved in determining brain size,  are microcephalin and ASPM. These genes were discovered because defects in them lead to micrcephaly, a devastating reduction in brain size and complexity. Recent research “has shown that both of these genes have undergone significant changes under the pressure of natural selection during the evolution of Homo sapiens.”Specifically,  “Microcephalin (without the defect) showed evidence of accelerated evolution along the entire primate lineage,” while “ASPM (also without the defect) has evolved most rapidly after the divergence of humans and chimps, implicating these genes as the cause of the rapidly exploding brain size of our ancestors.”

Gazzaniga clearly rejects the “brain size is all” approach to explaining differences between human thinking and the cognition of other primates, but he argues that the evolution of these genes parallels human cultural development.  Researchers tested the hypothesis that these genes may have continued to evolve in relatively recent times, finding that “one genetic variant of microcephalin arose approximately 37,000 years ago, which coincides with the emergence of culturally modern humans, and it increased in frequency too rapidly to be compatible with random genetic drift or population migration.” And “an ASPM variant arose about 5800 years ago, coincident with the spread of agriculture, cities and the first record of written language. It too is found in such high frequencies in the population, that it indicates strong positive selection.”

While in their EDGE papers Gazzaniga and Dehaene approach the study of the human brain with different tools and with different interests — the genetic roots of cognition and the mechanics of the onset of consciousness, respectively –they both argue that there’s something special about human cognition. Whether it’s the continuing evolution of the genes that generate higher consciousness or a global neuron workspace in which higher thought occurs, it seems that they would agree, in Gazzaniga’s terms, that human brains are, indeed, unique.

And, if V. S. Ramachandran is right, the cognitive experience of each of our unique human brains is itself unique. Not that this cools his enthusiasm for brain scans. But that’s for next time.

One thought on “Are human brains unique?

  1. We can agree that the human brain is unique but the argument is based on evolution which implies a common heritage for ape and other brains.The study of the unique qualities and the common heritage both have their place. Gazzaniga is expressing a lack if interest in what we have in common.

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