Human Evolution: Cerebral Cortex and Dentition Flashcards
Describe the size of the brain and cranium in comparison to that of apes
Humans – relatively large brains
Larger than apes
Difference associated with larger cerebral cortex
Physically larger
Has folds to increase surface area (convolutions)
Frontal lobe enlarged
Thinking, reasoning, planning, processing
Large brain requires large cranium
More of skull used for brain in humans than in apes
Brow more vertical, without ridges
Flatter face, more prominent nose
Describe the structures involved in the relative sizing of the cerebral cortex
Can see evolutionary trend towards greater cranium size and brain development in hominin ancestors:
Australopithecus afarensis cranium size more similar to modern apes, but has adaptations for bipedalism – indicates brain size increased AFTER bipedalism developed.
Can’t see brain of fossils, but can see cranial capacity, and sometimes endocasts showing convolutions on cerebrum (more on this later)
Gradual increase in relative cranial capacity as more closely related to humans.
Also foramen magnum positioning, rounding of skull.
Sometimes only skull fragments are found – can then be difficult to estimate cranial capacity.
What is an endocast?
*Endocasts
*Are “casts” of the inside of the skull – see image
*Provide shape of brain surface
*May occur naturally, or by scientific casts made of inside of skull
*Reveal increase in convolutions and relative size of frontal lobe
*Trend can be seen as hominin species become more recent
*Even within H.erectus –increase seen between earlier and later fossils
What is prognathism?
Prognathism: forward jutting jaw
What is dentition?
*Dentition: size, shape and position of teeth
Describe the dentition of humans and compare it to that of other hominin species
*Humans very distinctive compared to other primates
*Canines do not protrude or interlock – small canine teeth, no diastema
*Parabolic rather than U shaped dental arcade
*Change in dental arcade shape is a trend among hominin ancestors:
*A. afarensis lower jaw and face ape-like
*H. habilis molars and premolars smaller and narrower, still prominent canines
*H. erectus smaller and narrower, canines smaller
*Early H. sapiens had larger teeth than modern humans
Describe the evolutionary changes to the brow ridge and cranium and teeth in humans
*Evolutionary trend to flatter face, development of chin and more prominent nose.
*Gradual enlargement of frontal lobe led to more distinct forehead, reduction in brow ridge.
*Smaller teeth due to dietary changes led to smaller jaw and flatter face – also provides balance for bipedalism.
