The Human Advantage

In ‘The Human Advantage: How Our Brains Became Remarkable’, Suzana Herculano-Houzel weaves together two stories: the story of her scientific career, based on her invention of a new technique for counting the number of brain cells in an entire brain, and the story of human brain evolution.

Previously counts of neurons in brains of humans and other animals relied on sampling: counting the cells in a slice of tissue and multiplying up to get an estimate. Because of differences in cell types and numbers across brain regions, these estimates are uncertain. Herculano-Houzel’s technique involves liquidizing a whole brain or brain region so that a sample of this homogeneous mass can yield reliable estimates of total cell count. Herculano-Houzel calls it “brain soup”.

The Human Advantage is the story of her discovery and the collaborations that led her to apply the technique to rodent, primate and human brains, and eventually to everything from giraffes to elephants.

Along the way she made various discoveries that contradict received wisdom in neuroscience:
most species (including rodents primates) have 80% of the neurons in the cerebellum
humans have about 86 billion neurons (16.3 billion in cerebral cortex), which is a missing 14 billion neurons compared to the conventional estimate.
– you can’t compare brain size to count brain cells. Because the cell volume changes with body size, some species with bigger brains have fewer neurons, and species with the same size brains can have vastly different neuron counts.

Example 1
* The capybara (a rodent), cerebral cortex has a weight of 48.2g and 306 million neurons
* The bonnet monkey (a primate), cerebral cortex has a weight of 48.3g and 1.7 billion neurons

Example 2
* African elephant, body mass 5000 kg, brain mass 4619g, 5.6 billion cerebral cortex neurons
* Human, body mass 70 kg, brain mass 1509g, 16.3 billion cerebral cortex neurons

(Fun fact:elephant neurons are 98% in the cerebellum – possibly because of the evolution of the trunk).

A lot of the book is concerned with relative as well as absolute numbers of brain cells. A frequent assumption is that humans must have more cortex relative to the rest of their brain, or more prefrontal cortex relative to the rest of the cortex. This is not true, says Herculano-Houzel’s research. The exception in nature is primates, who show a greater density of neurons per gram of brain mass and more energetically efficient neurons in terms of metabolic requirement per neuron. Humans are no exception to the scaling laws that govern primates, but we are particularly large (a caveat is great apes, who have larger bodies than us, but smaller brains, departing from the body-brain scaling law that govern humans and other primates). Our cognitive exceptionalism is based on raw number of brain cells in the cortex – that’s the human advantage.

This is a book which blends a deep look into comparative neuroanatomy and the evolutionary story of the brain with the specific research programme of one scientist. It shows how much progress in science depends on technological innovation, hard work, a bit of luck, social connections and thoughtful integration of the ideas of others. A great book – recommends!

6 thoughts on “The Human Advantage”

  1. Although I’ve met people that probably have 16.3 cerebral cortex neurons, I think you’re missing the word “billion” in the elephant/human comparison!

  2. I’ve ordered the book but I wonder if there is anything in it about differences in neurological development. Specifically, it seems that much of human development occurs after birth and in a social context. Many skills, especially language, require stimulation from the social environment at specific times in development to create the connections. So is the advantage just simply more brain cells or more brain cells plus the social context of development.

    1. The weakness of the book is that it is a biological perspective rather than a cognitive one. The author references some abilities (e.g. delayed gratification) and behavioural ecological factors (e.g. hominid’s use of cooking, which allows our larger brains to be metabolically supported), but doesn’t go into a lot of detail. I think if you really want an angle on skills – including language – then you need someone who compares the functional neuroanatomy (ie what brain areas have been involved in which behaviours across species), which is not this book. Maybe a reader can suggest some good reading on what you’re interested in? If you haven’t read Deacon’s The Symbolic Species, I’d start there

  3. This book as practically all other books/studies presume that homo sapiens is the supreme criterion by which to judge other species. This is evidently an extreme example of anthropomorphism. Within it’s own pov many more animals are far superior within their own context than homo sapiens.
    In the realms of the disinterested natural evolutionary world homo sapiens is in evolutionary terms a dead end branch. It took the species a mere 100.000 years to arrive at the point where it is on the brink of multiple factors leading to extinction.
    Unbridled procreation, with a distinct tendency to self-destruction coupled a primal brain which controls an unrivaled capacity for mass destruction is not going to able to compete with even mere jellyfish which outlive us by 500 million years.
    Homo sapiens barely overcame in evolutionary time scales, it’s gene pool severely polluted by not only being descendant of the relative few that survived the multiple natural disasters such as the ice ages but nowadays by medicinal progress.
    Eugenetics is a dirty word because it was abused by an ideology of the 20th century but anyone with a sound mind can reason that keeping non-viable specimens in that gene pool only serves to pollute it even more.

    Homo sapiens has effectively put itself outside of the natural selection mechanism which as a mechanism caused the best specimens to survive and the weakest succumb. By intervening in this mechanism of we barely understand it’s long term implications it would surprise me if homo sapiens as a species would reach a million years let alone the 200 million years of the crocodile which so far made to 200 million years.

    Hubris will be it’s undoing long before

    1. This book never claims humans are unique or the standard by which animals must be judge – in fact it repudiates this exact view – so if you think it instead endorses this view you must have misread me and/or I must have ambiguously summarised the book

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