Hypoglossal Nerve Size

Certainty Style Key
Hover over keys for definitions:
True   Likely   Speculative
Human Uniqueness Compared to "Great Apes": 
No Difference
MOCA Topic Authors: 

The hypoglossal nerve (the 12th cranial nerve) supplies motor innervation to all of the intrinsic and all but one of the extrinsic muscles of the tongue. The hypoglossal nerve passes through the hypoglossal canal in the occipital as it exits the cranial vault. Humans have larger hypoglossal canals (both absolutely and relative to oral cavity volume) than other great apes, suggesting a larger hypoglossal nerve in humans. Given the role of the hypoglossal nerve in tongue movement, enlargement of the nerve in humans has been argued to reflect finer motor control of the tongue than possible in other apes, which is important to the rapid production of speech sounds in language. While the size of the hypoglossal canal is absolutely and relatively larger than that of other great apes (although in absolute terms the difference from gorillas is not statistically significant), relative to oral cavity size the human hypoglossal canal is smaller than that of gibbons. Recent studies also suggest that the size of the hypoglossal nerve itself may not differ between humans and chimpanzees.

Timing

Timing of appearance of the difference in the Hominin Lineage as a defined date or a lineage separation event. The point in time associated with lineage separation events may change in the future as the scientific community agrees upon better time estimates. Lineage separation events are defined in 2017 as:

  • the Last Common Ancestor (LCA) of humans and old world monkeys was 25,000 - 30,000 thousand (25 - 30 million) years ago
  • the Last Common Ancestor (LCA) of humans and chimpanzees was 6,000 - 8,000 thousand (6 - 8 million) years ago
  • the emergence of the genus Homo was 2,000 thousand (2 million) years ago
  • the Last Common Ancestor (LCA) of humans and neanderthals was 500 thousand years ago
  • the common ancestor of modern humans was 100 - 300 thousand years ago

Possible Appearance: 
2,000 thousand years ago
Possible Selection Processes Responsible for the Difference: 

Kay et al., 1998.  The hypoglossal canal and the origin of human vocal behavior. PNAS 95: 5417-5419.
DeGusta et al., 1999. Hypoglossal canal size and hominid speech. PNAS 96: 1800-1804.
Jungers et al., 2003.  Hypoglossal canal size in living hominoids and the evolution of human speech. Hum Biol 75: 473-484.

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