Homo amygdala?

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A Mind for Sociability:

The amygdala, a small, almond-shaped area deep within our brains, appears to be essential in helping us read the emotions of others. Research shows that the structure is crucial for detecting fear, but scientists have also found evidence that it can help spot a wide variety of mental states…scientists noted that the amygdalas of patients with autism, which is characterized by decreased social interaction and an inability to understanding the feelings of others, have fewer nerve cells, especially in a subdivision called the lateral nucleus.

In humans, however, the lateral nucleus occupied a bigger fraction of the amygdala, and was larger compared to overall brain size, than in the other species, the team reports online today in the American Journal of Physical Anthropology. Although the functions of the amygdala’s subunits are unclear, the lateral nucleus makes more direct connections with the brain’s temporal lobe–which is involved in social behavior and the processing of emotions–than other parts of the amygdala make, the researchers note.

In Grooming, Gossip, and the Evolution of Language Robin Dunbar argued for the critical selective pressure of social groups in driving up the size and complexity of the human brain (and obviously, the emergence of language). This might explain the gradual increase in brain size over the past few million years until about 200,000 years B.P., but what about the Great Leap Forward & expansion out of Africa ~50,000 years ago? Remember, behaviorally modern humans postdated anatomically modern humans (e.g., a form of H. sapien which was gracile, high cranial vault, etc., was extant in Africa before expanding to the rest of the world) by 150,000 years. In The Dawn of Human Culture Richard Klein suggests that there was a biological change, a reorganization of the brain (Dunbar offers this idea as well). Greg has suggested that Neandertal introgression & hybrid vigor might have been at work; remember that Neandertals had the largest cranial volume of any Homo species. In The Prehistory of the Mind: The Cognitive Origins of Art, Religion and Science Steven Mithen suggests that the breakdown of separation between domain specific intelligennces (e.g., social intelligence, theory of mind, intuitive physics, folkbiology, etc.) was the critical factor in triggering the cultural revolution which lead to modernity. Mithen argues that the use of analogy to map across the various domains, and apply insights from each domain to the others, might have resulted in a massive increase in cognitive flexibility and creativity. A neurobiological implication that our species’ amygdala is more “hooked in” with our “higher cognitive functions” seems to lend some credence to that viewpoint.

Update: Kambiz has more.



  1. I wonder, what about the amygdalas of dogs and cats?

  2. domesticated dogs would be interesting….

  3. google says the main diff is gene expression in the hypothalamus in terms of wolf vs. dog.

  4. temporal lobe is famous for memory and maybe navigation.. higher cognitive functions are more often put up front..?

  5. now that i look.. the authors of the amygdala study aren’t all that fond of the prefrontal cortex story for humans. 
    We tested this idea and found that humans have only 2% plusminus 28 more prefrontal white matter than expected for a primate of similar prefrontal gray matter volume (Fig. 1b). On the basis of a prediction calculated from only great ape data, the human values are actually 17% plusminus 35 lower than expected. Given these results, it is difficult to make a strong claim for the evolution of specialized human enlargement of prefrontal white matter beyond simple allometric scaling to maintain functional interconnectedness at a larger overall brain size. Specialization of cortical neuron types8 and elevated gene expression associated with metabolism and synaptic plasticity9 in humans suggest that subtle modifications of architecture, function and connectivity10 may have been critical in the evolution of human cognitive capacities.

  6. I’m not sure why migration out of Africa has to be linked to GLF. Doesn’t it seem more likely that this resulted from the need to expand hunting/gathering range, or from climate change/opening of a desert barrier to expansion? 
    Admittedly migration into New Guinea and Australia needed technological development suggesting an increase in cognitive ability, but the initial migration out of Africa would not seem to need it. Also, anatomically modern humans migrated out of Africa into the Middle East once previously (>100,000 years BP) but apparently failed to survive there in competition with H. neanderthalensis. 
    Increased cognitive ability and a more advanced tool kit, complex language, social development and better navigational ability may have made migration more successful, but would not seem to be a prerequisite to migration itself, or whatever prompted it. 
    And 50,000 years does seem on the low side – regardless of the Mungo interpretation, it is at least 45,000 years, which suggests 50,000 years BP for the initial expansion out of Africa is on the low side.