Human Evolution

Ch 17.6 “wolf book”

• The narratives of human evolution are oft-told and highly controversial. There are major disagreements in the field about whether human evolution is more like a branching tree or a crooked stick, depending partly on how many species one recognizes.

• Interpretations of almost every new find will be sure to find opposition among other experts. Disputes often center on diet and habitat, and whether a given animal could walk bipedally or was fully upright.

• We do know that by the time the animals known as Homo evolved, they could make tools, and their hands were well suited for complex manipulations. These features were eventually accompanied by the reduction of the lower face, particularly the jaws and teeth, the recession of the brow, the enlargement of the brain, the evolution of a more erect posture, and the evolution of a limb more adapted for extended walking and running (along with the loss of arboreally oriented features).

• Human evolution should not be seen as a simple linear progression of improvement toward our own present-day form. You will see differences in cladograms.

I. We belong to the Primate order along with lemurs, monkeys, chimps and apes!

A. Primate Characteristics & Significance

1. Flat face with forward facing eyes: binocular vision! Allows for depth of field (3-D). Allows to jump over and to other places and catch, etc

2. Flexible shoulder and hip joints: freedom of movement, swinging, bipedal motion (height to be able to see)

3. Well-developed cerebrum: complicated behavior, societal actions, tool development

4. Opposable thumbs: grasping of branches, tool use

II. Primate Origins and Organization

I. modern primates evolved from a common ancestor that appears in the fossil record about 65 MYA.

A. Primates are divided into two groups:

1. Prosimians

a. Includes: bush baby, lemurs, lorisis

b. Characteristics: small, nocturnal, tree-dwelling, large eyes, arms shorted than legs.

2. Anthropoidsa. New World Monkeys: almost exclusive

living in trees, prehensile tail (5th hand), Central and South America. (Squirrel monkey, spider monkey)

b. Old World Monkeys: More ground dwelling, no prehensile tail, legs longer than arms, Asia & Africa (baboons, macaques)

c. Great Apes: ground and tree, no tail, arms longer than legs, Gibbons, orangutan, gorillas, chimpanzees

d. Humans: ground dwelling, no tail, lack of body hair, large cerebrum (thinking part of brain), bipedal

III. Ancestry of Homo sapiens

A. Hominids:

1. Currently, there are 5 genera and 16 different hominid species in the fossil record and the fossils span about 4.5 million years.

2. All of these species are relatives of modern humans, but not all are ancestors.

B. Hominid History:1. Austrolopithecus (genus)a. 4 MYA – 1 MYAb. human-like primate that was

bipedalc. well known fossil named “Lucy”

– 3.2 myo2. There are other genera (plural

for “genus”) that are not direct ancestors but are “dead ends” on our family tree meaning that the members of these particular genera died out.

3. Homo habilisa. first member of our genus

b. appeared 2.5 MYA in Africa

4. H. habilis was followed by

H. ergaster and H. erectus

a. H. erectus began migrating out

of Africa and by about 1.8 MYA

were living in many areas in Asia.

b. Survived a very long time

5. So where do H. sapiens (aka” us/we) come in?

a. Most scientists support an “out of Africa” hypothesis which proposes that the first true Homo sapiens appeared about 200,000 – 150,000 years ago in Africa and then migrated all over the world replacing H. erectus populations.

b. Data based on mitochondrial DNA strongly supports this hypothesis and points to a single African origin for all modern humans.

• Extra note: We often talk about the Neanderthals in human ancestry. H. neanderthalensis evolved from the same ancestors as H. sapiens and these two species lived side by side until about 50,000 years ago when the Neanderthals died out…why is not yet known…