How We Study Hominid Evolution

Review of Taxonomy

• Linneaus: Binomial Nomenclature • Genus and species (Homo sapiens) • Also higher order taxa (categories) • Each category implies a similar type of adaptation (remember what that means?)

The Family Hominidae (Hominids) • Humans & our most recent ancestors • Primary Characteristic – “obligate” bipedalism • As they evolved – increased brain to body ratio

The Family Hominidae (Hominids) • Consists of multiple genera • We will focus on three: 

Ardipithecus



Australopithecus



Homo

Ardipithecus

1 species we will study: -

Ardipithecus ramidus

Australopithecus

4 species we will study: -

Australopithecus afarensis

-

Australopithecus africanus

-

Australopithecus boisei

-

Australopithecus robustus

Homo

3 species we will study: -

Homo habilis

-

Homo erectus

-

Homo sapiens

Species Definitions

Biological species can mate and produce offspring that are capable of reproducing

But what if the species are extinct?

Morphological species Distinguished on the basis of their morphological features (which reflect their environmental adaptations)

So…

We will be looking at the various hominids primarily with respect to their morphology But since form is related to function… We will thereby be considering how each species behaved

Mosaic Evolution

• Different parts of an organism evolves at different times and different rates • Homeobox (control) genes – Control one suite of traits but have little or no effect on others – SRY (sex Determining region y) gene ( located from base pair 2,786,854 to base pair 2,787,740 on the Y chromosome)

Three Parts of Our Mosaic Evolution • cranial capacity • the dentition & chewing apparatus • the bipedal adaptation

Cranial Capacity

• interior volume of brain case • measured in cubic centimeters (cc or cm3) • approximate estimate of brain size

Definitions: Cranium

• Cranial: Bones of the skull • Foramen magnum: where spinal cord enters brain cavity

Dentition/Jaw

• 2:1:2:3 dental formula • Diastema: gap in teeth Figure 11.10a

U-shaped

Dental Arcade

Shape of jaw Parabolic Figure 11.10a

Dentition/Jaw

• Simian shelf: buttress of bone under lower incisors (supports jaw in chewing) • Sagittal crest: ridge of bone at tone of skull where muscles for mastication attach

Bipedalism

The central adaptation of the Hominids

Figure 05.17

Figure 05.19d

Figure 05.20

Cranial Indication of Bipedalism position of foramen magnum

Figure 05.27

Why Bipedalism?

Why Bipedalism?

The Study of Hominids

• Is the study of our own lineage • Subject to emotional interpretation • Conscious and unconscious biases

Questions, Questions • What drove the changes leading to humans?

– Was there a “prime mover”?

• What makes us human?

– What anatomical aspects of ourselves truly set us apart from other animals?

• 1912

The Lesson of Piltdown

• Skull (large brain) • Jaw ( ape-like)

The Piltdown Hoax

• FRAUD!

• Human Skull • Orangutan jaw

The Lessons of Piltdown • Fluorine analysis is a useful dating method • Let fossils speak for themselves!

Figure 05.32a

Figure 10.18