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!