Sutures of the skull

I’ve made lots of claims for prehistoric species of mankind being intelligent and even meriting the label ‘sapiens’.  There is circumstantial evidence for this; is there any direct evidence for it?

Complex sutures seen on both modern and fossil skulls may be direct evidence of a human level of thinking.  Ape skulls have sutures but these are much simpler.

The bony plates of the cranium are joined together by cartilage.  When the brain stops growing, this cartilage changes into bone and the cranial plates fuse together.  When this happens the sutures start to disappear and the skull appears to made of one piece.

In apes the sutures fuse early in life, but in humans the sutures may remain open well into adult maturity.

As an individual learns things, their cerebral cortex grows and both the grey matter and white matter increase in volume.  This causes pressure that stops the sutures from closing.  Not only do the sutures with their cartilage not close, but they also pull apart.  This process causes the sutures to have a serrated effect.

Paul Broca provided a typology of suture complication in 1875 so that skulls could be described.  Sutures may be simple, harmonious and denticulate.  The width of sutures show various grades of complication.

Sutures are developmental features that increase the size of the skull through behaviour rather than through genetic inheritance.

As an individual thinks, the cerebral cortex expands as new connections are made between neurons; the cortex convolutes beneath the cranial plates and pushes on the plates; the joins between the plates at the sutures pull apart with cartilage forming in the gaps, and the process continues sometimes late into life forming extremely complex sutures.

The degree of sutural complication relates to how much that individual used their brain for problem-solving.  A number of prehistoric skulls possess these features.

  • Sterkfontein 5 and MLD 37/38 from South Africa are classified as Homo primocreatus / australopithecus.  Sutures show a fair degree of complication, although they started to fuse at the end of youth.
  • Cranium 3, 4 and 5 from Sima de los Huesos classified as Homo praecursor heidelbergensis / Homo heidelbergensis.  The sutures are quite complicated in places.
  • Eguisheim skull is a Cro Magnon / Homo aequalis fossilis from the Post Ice age period.  It has highly complicated posterior sutures infilled with wormian bones.  The skull can be extended by 1 -2 cm in the places of these extensions.

Denticulate sutures in fossil skulls give an indication of human intelligence in prehistoric species as these developmental features only develop with use of the brain in a human degree of thinking.

I rest my case for prehistoric human intelligence upon these fossilized brain cases.

SH 4 from Sima de los Huesos, Atapuerca showing suture complication for Homo praecursor heidelbergensis

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