Human evol

Human evolutionAditi Pai

"Hominid" refers to members of the human family, Hominidae, which consist of all species from the point where the human line splits from apes towards present day humans.

Habitual bipedal locomotion (movement on two legs), an upright position, and a large brain that has lead to: tool use, language, and culture characterize hominids.

Human evolution

A. History

B. Important stages in human evolution

C. Theories of human evolution

D. ‘Human Characteristics’

E. Are we still evolving?

History

• 1856-Neander Valley– Discovery of a skull that was not quite human

• 1859 – Darwin publishes ‘The Origin of Species’

• 1871- Darwin predicts that ancestors of humans would be found in Africa

• Up till 1930s– Humanity evolved

in Europe

• 1950s--1960s– Many significant

fossils discovered

ABC D

ABCD

Bush model

Linear model

• 1970s – present– more fossils – molecular

techniques– ‘tree model’ of

human evolution

Current Controversy

6-7 m y old fossil

Earliest bipedal hominid?

Sahelanthropus tchadensis

Important stages in human evolution

1. 3.2 million years ago

2. 3 million years ago

3. 2 million years ago

4. 1 million years ago

5. 200, 000 years ago

6. 150, 000 years ago

"Hominid" refers to members of the human family, Hominidae, which consist of all species from the point where the human line splits from apes towards present day humans.

Habitual bipedal locomotion (movement on two legs), an upright position, and a large brain that has lead to: tool use, language, and culture characterize hominids.

3.2 mya: The southern ape of afar

• Fossil: – “Lucy” (discovered

1974, Ethiopia)

– Australopithecus afarensis

Male

Fossil of “Lucy”

Female

Australopithecus afarensis

• Habitat: savannah and woodland

• Food: leaves, fruit, seeds, nuts, termites and eggs, grasses (?)

• Physical characteristics: – low forehead, flat nose, no chin– small brain– long dangly arms, short legs– facultative bipedal (upright on ground but could

dangle from branches)– sexually dimorphic

Paranthropus boisei Homo habilis

3 mya: Paranthropus boisei

• Habitat: open terrain

• Food: nuts, roots and tubers

• Physical characteristics: – enormous jaw with chewing muscles, – large back teeth, small front teeth– specialized as vegetarians

• Not direct human ancestors

3 mya: Homo habilis-the ‘handy man’

• Habitat: open terrain

• Food: Scavenged for meat

• Physical characteristics:

– small jaw and teeth

– shorter arms

– increase in brain size (because of

carnivorous diet and mode of feeding)

– capable of speech

Oldowan Tools

Made tools

Human migration

• 1.9 mya humans began to leave Africa to other continents

Homo ergaster

2 mya: Homo ergaster

• Habitat: dry -hot habitat

• Food: scavenger for meat

• Physical characteristics: – Tall with long limbs

– Smooth and dark skin • Temperature regulation through sweating

– Narrow pelvis (lead to narrow birth canal)• Mothers needed support of partner and group to raise babies

Acheulean bifaces

Homo erectus

• brain, almost human size

• stocky, human-like body (larger than Homo habilis)

• Java, China, and Africa

• use of fire

• increased but infrequent group hunting

• language

• crude shelters and some migration to colder areas

• used tools

Homo erectus

Homo heidelbergensis

1mya: Homo heidelbergensis

• Food: hunted for meat

• Physical characteristics: – Large brain

– Tall

• Direct ancestors of Homo sapiens

Boxgrove tools

H.heidelbergensis made Hand axes, wooden spears etc.

200,000 ya: Homo neanderthalensis

male female

200,000 ya: Neanderthal man

• Habitat: cold • Food: hunted for meat• Physical characteristics:

– Large face with massive ridges– No chin– Short stocky body (conserve heat)– Muscular

• Language• Social relationships important

What happened to the Neanderthals?

• Extinct 28, 000 ya

• Competition from Homo sapiens?

• 120, 000 ya • Physical characteristics:

– Eyebrow ridge small or absent– Prominent chin

• Tools --antler, bone, stone• Clothing, jewelry, artwork, musical

instruments

Homo sapiens

Theories of human evolution

• Humans evolved in sub-Saharan Africa and spread from there

or

• Humans evolved independently in several places around the globe

Out of Africa hypothesis

• Homo sapiens evolved in a single speciation event in Africa ~ 250, 000 ya

• Migrated to other regions, replaced Homo erectus

Multi-regional hypothesis

• Local populations of Homo erectus evolved into Homo sapiens

• Mixed genes

• Retained local characteristics

Support for multi-regional hypothesis

• No break in culture in S.E Asia

• Can explain the occurrence of regional characters

Races• Original skin color- black

• Divergence from original black color to many different colors

How different are the races?

• No genetic discontinuities between races

• Genetic differences between races only

10% of genetic diversity among humans

• No evidence for major biological

differences

Support for ‘out of Africa’ hypothesis

1. Level of diversity in maternally inherited mitochondrial DNA of humans from around the world highest among Africans

2. Based on genetic diversity all non-Africans descended from a small band of humans that left Africa ~ 100, 000 ya

Support for ‘out of Africa’ hypothesis

3. The Y-chromosome too shows no sign of any non-African DNA

Support for ‘out of Africa’ hypothesis

• Australia --- ~60,000 ya

• Europe --- ~70,000 ya

• Near East --- ~90,000 ya

• Africa --- ~130, 000 ya

Human migration

Who were the first Americans?

• 13,000 ya

• Crossed Bering Strait

Human characteristics

• Bipedal gait

• Big brain

• Tool making

• Social relationships

• Art

• Culture

Bipedalism• When?

– Before Australopithecines

• Advantages: – Freed hands to carry objects – See predators better in grasslands– Access to foods not previously available– Carry children– Protection from sun in grasslands

Evolution of bipedalism

1. Carrying objects

2. See predators

3. Aquatic environment (?)

Evolution of big brain

• Meat eating from Homo habilis onwards– Did not require large intestines– Energy freed up for other organs including

brain

or

• Cooked tuber eating in Homo erectus– Hunter-gatherers rely less on meat than

tubers– Reliance on scavenged meat is difficult.

Tool making

• Homo habilis onwards

• Tool-making was considered a ‘human trait’– Discovery of tool-making in

chimpanzees

– Tool making in Australopithecines?

Homo sapiens survived extinction in late Pleistocene– ‘bottlenecks’ (drastic reduction in

population size )– cultural explosion– Societies became co-operative (‘troop-to-

tribe transition’)

Social relationships, art, and culture

Are we still evolving?