Humanity and the left hemisphere: The story of half a brain

ABSTRACT

Until fairly late in the nineteenth century, it was held that the brain was bilaterally symmetrical. With the discovery of left-brain dominance for language, the so-called “laws of symmetry” were revoked, and asymmetry was then seen as critical to the human condition, with the left hemisphere, in particular, assuming superordinate properties. I trace this idea from the early discoveries of the late nineteenth century through the split-brain studies of the 1960s, and beyond. Although the idea has persisted, the evidence has revealed widespread cerebral asymmetries in nonhuman animals, and even language and its asymmetries are increasingly understood to have evolved gradually, rather than in a single speciation event. The left hemisphere nevertheless seemed to take over a role previously taken by other structures, such as the pineal gland and the hippocampus minor, in a determined effort to place humans on a pedestal above all other species.

KEYWORDS:

• Animal asymmetry
• human uniqueness
• language
• left hemisphere
• split brain

Disclosure statement

No potential conflict of interest was reported by the author.

Notes

1 Jaynes completely overlooks peoples from other cultures. The Australian aboriginals, for example, were isolated for some 70,000 years, and were therefore far removed from the critical upheavals of the second millennium BCE.

2 He later specified protocadherins 11X and 11Y as the actual loci (Priddle & Crow, 2013).

Additional information

Funding

This work was supported in part by grant number 3701584 from the Marsden Fund, administered by the Royal Society of New Zealand.