Tag: brain size

Sutures of the skull

by clarevmerry, posted in human intelligence

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

How did the human skull evolve increasing size?

by clarevmerry, posted in human intelligence

Human evolution shows an increase in cranial capacity – the question is, how did this come about?

The answer is:

  • The development of the skull became delayed so that the fetal condition continued long after birth with fontanelles remaining open for longer.
  • The skull bones became thinner in modern humans compared to most prehistoric species and this allows for moulding during birth.
  • The female pelvis became bigger in wide-bodied populations so babies with larger heads could be born.

Compared to animals, human babies are born helpless and dependent on the parents for protection to a much higher degree.  Human babies are born with holes in their skulls that have only cartilage and membranes covering the brain, with no bone.  These holes are called fontanelles. 

Fontanelles allow for two things:  Firstly, they allow the baby’s head to be deformed during birth as it moulds during the descent down the birth canal.  Secondly, the skull grows outwards from these holes and from sutures between cranial plates.  The longer the fontanelles stay open, the more the skull can grow outwards from them.

This delayed pattern of growth – with the fetal condition being retained after birth – is the human pattern of growth.  It is called secondary altriciality.  By the time ape babies are born their fontanelles have almost closed up.  In the human baby the fontanelles remain open for the first year and the infant’s brain grows at fetal rates during this year.

The human pattern of growth is found in Homo ignis / Homo erectus.  We can infer that babies of this species were born with open fontanelles from two million years ago.  This allowed cranial capacity to increase to 800 cc or more.

My own calculations, which will appear in a book I am currently editing, show that Homo primocreatus – Primordial Man had an intermediate degree of secondary altriciality compared to apes.  There would be a small delay in development.

Homo ignis / Homo erectus had thick skull bones and well-developed browridges.  He and she lived in a world where being clubbed over the head by an enemy was a real possibility.  Survival was dependent on a reinforced skull.

Gracilization of the skull came with Homo aequalis / Homo sapiens  100 000 years ago – I think due to internal tribal peace and a new set of weapons used against enemies.

Thinner skull bones meant that the head of a baby could mould during childbirth, thus a child with a larger head survived the birth process.  It also meant a more delicate infant requiring more protection from falls.

An alternative way of having babies with larger heads was for the female bony pelvis to become more ample.  This seems to have been the way forward for Homo centralis / Neanderthal.  These were wide-bodied people with ample pelvis for childbirth.  The skulls of Neanderthals had thick bones so they must have achieved large cranial capacity by this alternative method.

In modern people all of the above traits are combined such that women give birth to infants whose skulls mould as they are born, and continue to develop at a high rate after birth.  The combination of traits has increased cranial capacity over the course of human evolution to what we consider normal today.

Top view of skull of human new born showing the fontanelles
Cranial plates and fontanelles in the human new born

The evolution of brain size

by clarevmerry, posted in human intelligence

Human evolution in the direction of Homo sapiens has essentially been couched in terms of an increase in brain size.  Measurements of prehistoric fossil skulls done by anthropologists show the cranial capacity for different prehistoric species of mankind.  The volume of the brain case was measured with no. 8 shot or with mustard seed in the 19th century.  Cranial capacity is larger than the size of the brain that would have been inside it.  For example, the average cranial capacity today is 1400 cc and the average brain weight is 1330 grams.

There was a steady increase in cranial capacity in prehistoric species.  This is a summary of the facts of physical anthropology:

  • Chimpanzee average brain size is 380 cc (cubic centimetres) [included for comparison]
  • Homo primocreatus / Australopithecus 450 to 500 cc
  • Homo habilis 700 cc
  • Homo ignis / Homo erectus / Homo ergaster 800 to 1100 cc
  • Homo ignis antecessor / Homo erectus 1100 cc
  • Homo praecursor heidelbergensis / pekinensis / afarensis / Homo heidelbergensis 1200 cc with a range of 1100 to 1400 cc
  • Homo centralis / Neanderthal range of 1250 to 1750 cc
  • Homo aequalis / Homo sapiens of 100 000 years ago 1500 cc
  • Homo aequalis fossilis Cro Magnon man  1570 cc
  • Homo aequalis / Modern Man  1400 cc

The evolutionary thesis is that as the brain evolves and increases in size, the animal evolves into a human.  The bigger the brain, the more human the creature.

There is, however, a problem with this.  The brain of Neanderthal was larger than the global average today but he was denied the status of being human.  It was said he could only grunt and not talk, no wonder that this brute went extinct when our species came along.

It was later found, with advances in genetics, that we in Europe carry a percentage of Neanderthal genes.  This either means that we are part-animal or that Neanderthal was human after all.

Christians who adopt an evolutionary perspective on creation and an evolutionary origin for humans have more of a problem than most with human evolution.  From a Christian perspective a human person is not an animal and a human person has a soul.  Some Christians have resolved the issue by dropping belief in a human soul, but for those who still believe that to be created in the image of God is to have a soul – at what point did souls enter the human being?

The narrative goes that an ape-man managed to become far enough evolved and get a big enough brain for God to consider this creature to be worthy of being given a soul.  From then on ensouled humans had moral responsibility for their actions.  Ironically they wiped out all the hominids without souls causing them to become extinct.

For me the above question is totally meaningless.  And the answer given has quite horrific implications – firstly that there could be a creature looking just like a human that had no soul and therefore was simply an animal – although you would have no way of distinguishing between the human and the animal just by looking at them.  Secondly, the highest gift of a soul becomes the justification for mass hominidcide, and this is presented as a good thing.

My alternative thesis is that:

  1. There is no threshold brain size for possession of a soul or for being a morally responsible being.
  2. If you have a soul, you are human.  The soul is whole and in every part, there are no part-souls.  Likewise there were never any hominids part-way to being human.
  3. Even with a cranial capacity only marginally above that of apes, a human life is still possible.

Therefore, all prehistoric species that have been classified as ‘hominids’ or ‘hominins’ have, in fact, been human beings adapted to various sets of circumstances that are not found today.  They have all been peoples with culture, and persons with souls.

I had already reached this conclusion when Homo floresiensis was found on the Island of Flores, Indonesia in 2004.  The skeleton found had a cranial capacity of 380 cc and a stature of one metre.  The find was classified as a dwarfed Homo erectus, but the surprise was that it was dated to only 18 000 years old. 

Homo floresiensis is confirmation that a being with a cranial capacity the same as chimpanzees, can, in fact, be human and have lived not long ago.  The human bones were found in a cave with evidence of fire, stone tools and animals that had been hunted.

Humans are human because they have a soul.  Even the most primitive humans had souls so any being looking like a human had a soul.  There was never a situation of Homo sapiens possessing a soul confronting hominids lacking a soul.  Human evolution has brought about changes to the physical body, but not to the fundamental identity of the human being.