Chapter 10, Early Hominid Origins and Evolution: The Roots of Humanity What is a Hominid?

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Chapter 10, Early Hominid Origins and Evolution: The Roots of Humanity

What is a Hominid?

Bipedal Locomotion: Getting Around on Two Feet

Evolved before large brain size

Walking on two limbs (with associated skeletal changes)

Origin or Bipedalism: Three Hypotheses

Hypothesis 1: Darwin’s Hunting Hypothesis

Bipedalism freed the hands for carrying weapons.

Intelligence increased; size of canines diminished.

Tool production & use essential for development of human intelligence.

New evidence shows this not to be the case.

Hypothesis 2: Rodman and McHenry’s Patchy Forest Hypothesis

Human origins and bipedalism related to the greater efficiency in some habitats of moving on two limbs rather than four.

Bipedalism arose in areas where forests were fragmented and food resources also

became scattered.

As forests fragmented, bipedalism freed the hands to pick up food allowing for both

tree and ground food resources to be exploited.

Hypothesis 3: Owen Lovejoy’s Provisioning Hypothesis

Freeing the hands was important in allowing males to assist females more

efficiently in procuring food; thus “provisioning” acted as a form of sexual

competition among males for females.

Birth spacing would also be reduced, since females would have to move around

less and would have access to greater food resources.

Lovejoy’s hypothesis makes the argument for monogamous fathers.

Bipedality had its benefits and costs” An evolutionary tradeoff

Bipedalism was a clear advantage to early humans.

It allows for a better view of the horizon, but also exposes the individual to predators.

Walking along with lifting or carrying heavy loads can cause back injuries.

The circulatory system also faces a greater burdern.

Loss of Sexual Dimorphism

Many primate species are highly sexually dimorphic, with males larger than females.

Some scientists see little sexual dimorphism in early hominids; therefore males would have

been more cooperative and less competitive.

Who Were the First Hominids?

The Pre-Australopithecines: Sahelanthropus tchadensis

Located in central Africa and dated to 7–6 mya
Brain size (cranial capacity) of 350 cc
Foramen magnum indicative of likely bipedality
Non-honing chewing complex
Close to pongid/hominid divergence

The Pre-Australopithecines: Orrorin tugenensis

Located near Lake Turkana and dated to 6 mya
Femurs indicative of bipedalism
Curved hand phalanx, suggesting time spent in trees
Nonhoning chewing complex
Lived in a forest

The Pre-Australopithecines: Ardipithecus kadabba and Ardipithecus ramidus

Located at Aramis and dated to 5.8–4.4 mya
Partial skeleton, other bones, and teeth
Variation in tooth wear; possessed thin enamel
Lived in a forest
Time spent on ground and in trees

The Pre-Australopithecines” Australopithecus anamensis

Located at Lake Turkana and Ethiopia and dated to 4 mya

Physically somewhat similar to Ardipithecus
Large canines, parallel tooth rows, different cusp pattern on lower first premolar

The Australopithecines (4–1 mya) : Australopithecus afarensis (3.6–3.0 mya)

Located in Laetoli and Hadar (found first in Hadar) and dated to 3.6–3.0 mya
Lucy (type specimen) is very complete for the age, 40 percent of skeleton found
Bipedal but with shorter legs, resulting in a slightly different stride
Long arms, curved finger bones, suggesting tree use
Cranial capacity of 430 cc
At Laetoli, assemblages include hominids as well as footprints of three hominids
Lived in varied habitats

The Australopithecines (4–1 mya): Australopithecus (Kenyanthropus) platyops (3.5 mya)

Found at Lake Turkana and dated to 3.5 mya
Woodland habitat
Flat face with some primitive characteristics

Evolution and Extinction of the Australo-pithecines: Australopithecus aethiopicus and Australopithecus boisei

Found in several locations in Africa
A. aethiopicus dates to 2.5 mya and had a cranial capacity of 410 cc
A. boisei dates to 2.3–1.2 mya and had a cranial capacity of 510 cc
Smaller front teeth, larger back teeth
Sagittal crest for attachment of chewing muscles
Dietary focus on harder foods
Evolutionary dead end

Evolution and Extinction of the Australo-pithecines: Australopithecus africanus

Found at Taung, South Africa and other sites, dating to 3–2 mya
Larger teeth than A. afarensis
Brain size of 450 cc

Evolution and Extinction of the Australopithecines: Australopithecus robustus

Found in South Africa and dated to 2 mya
Large premolars and molars, with a large face and sagittal crest
Similar to East African forms
Brain size of 530 cc

Australopithecus garhi (2.5 mya): First Maker and User of Tools

Located in Ethiopia and dated to 2.5 mya
Bones, teeth, partial skeleton, and a skull
Larger teeth than earlier australopithecines
More humanlike humerus-to-femur ratio
Cranial capacity of 450 cc
Probable ancestor of Homo
Associated mammal bones with cutmarks, leading to conclusion that A. garhi made
Oldowan tools, the earliest stone tools.
Stone tools long associated with meat consumption; some wear may indicate tools were
also used for digging in ground.

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