Hominid Traits
Human Biology and Forensics
January 4, 2011
REVIEW
• Many forms of evidence of evolution
– Comparative Anatomy
• Homologous Structures
• Vestigial Structures
– Embryology
– Biogeography
– Comparing Macromolecules
– Fossils
• QUIZ ON FRIDAY
REVIEW
• Review Primate Phylogeny
• We are all:
– Anthropoids
– Catarrhines
– Hominoids
– Hominids
HOMINIDS
• We are going to examine what happened with
humans when we diverged from the other
hominioids (pongids and hylobatids – apes).
• This occurred about 5 million years ago
HOMINIDS
• We split from our ape-like ancestors 5 – 7 mya
• Hominids refers to humans and human like
ancestors
HOMINID TRAITS
• What distinguishes humans from the apes?
• Two major features:
– Big brains
– Bipedalism
• These are features that we can identify in the
fossil record
BIG BRAINS
• We are going to look at differences in brain
size and structure
• These all support the HOMINID TREND of BIG
BRAINS
BIG BRAINS - 1
• Brain size got larger
– Brain size grew from 300cc to 1400cc
– Brain size can be measured by measuring inside of
skull/brain case
BIG BRAINS - 2
• Brain case changed shape
– Brain case was oval and bun shaped
– No forehead  more forehead
– With larger brains, rounder brain case
BIG BRAINS - 3
• Less postorbital constriction: Less separation
of brain and face
BIG BRAINS - 4
• Face got flatter
– Less separation of brain and face
– Less prognathism (snoutiness)
– Apes were snouty, humans have face tucked in
under the skull
– Losing the wisdom tooth.
BIG BRAINS - 5
• OTHER THINGS TO LOOK FOR:
– Sagittal Crest: mohawk of bone on top of head
– Nuchal crest: base of skull – thick muscle
attachment
– Wide flaring zygomas:
cheekbones; chewing muscles
SIGNIFICANCE OF BIG BRAINS
• More capacity for learned behavior
• More culture, more technology
BIPEDALISM
• What is bipedalism?
– Humans walk on two legs
– Not just walk – but striding bipedalism
– Swinging and shifting weight from leg to leg
– This has led to lots of anatomical compensations
• Now we will look at different forms of
evidence for bipedalism
BIPEDALISM - 1
• Foramen magnum
– Hole at the bottom of head, not off to back
– Good for looking straight ahead, 4 footed animal
can’t see if foramen magnum is at bottom of
head.
BIPEDALISM - 2
• Different vertebrae sizes
– Smaller at top (cervical)
– Medium (thoracic) with ribs
– Large (lumbar) support
weight of body
– Quadruped have same
vertebrae sizes
BIPEDALISM – 3
• Curves in spine
– Spine curves
– This supports weight as walk
BIPEDALISM – 4
• Bowl shaped pelvis
– Quadrupeds have flat blades and weight is
supported by rib cage
– Bowl shaped pelvis holds up guts and weight.
– Problem for birthing
– Best way to tell if human
BIPEDALISM - 5
• Angled femur
BIPEDALISM – 6
• Large legs in relation to arms
– In contrast to brachiating gibbon
– Femur is biggest bone in body
BIPEDALISM – 7
• Foot changes
– Big toe is not opposable
– Walking and balancing, not clinging in trees
– Arches in foot to support weight
– Laetoli footprints
WRITE NOW
• Answer the question about hominid traits
• 1. TRAIT ONE
– Evidence for Trait 1
– Evidence for Trait 1
• 2. TRAIT TWO
– Evidence for Trait 2
– Evidence for Trait 2
Problems with Bipedalism
• Hard to balance on two
feet – falling over all the
time; especially when
older
• Bad backs, lots of back
pain and injury
Problems with Bipedalism
• Hard to have children
– Baby’s head is very large (big brains!)
– Birth canal got smaller as a result of bipedalism.
– Many mothers crippled since pubis bone was
broken
– TIGHT FIT
Problems with Bipedalism
• Hard to have children
– Babies come out half cooked; skull is mainly
cartilage and baby’s head squeezes out of birth
canal.
– This means that baby has to rely on mother
(mother infant bonding and nurturing already a
primate trait)
– Can also bind head!