THE BIG PICTURE…timeline of human evolution

4.5 billion years ago: earth forms

4 billion years ago: first life (simple cells; 3Byr photsynthesis; 1Byr multicellular organisms)

500-600 million years ago (MYA) ‘Cambrian explosion’: insects, vertebrates…

150 million years ago (MYA)

• First mammals

55 million years ago (MYA)

• Dinosaur extinctions; ‘replaced’ by mammals, including first primitive primates (lemurs, tree shrews)

8 - 6 MYA

• First great apes (gorillas) evolve. Later (5-6MYA), chimp and human lineages diverge

6? - 4 MYA

Ardipithecus , chimp-sized brain, 300 and 350 cm³

4 MYA

• Australopithecines appear. They have brains scarcely larger than a chimpanzee's - with a volume around 400 - 500 cm³ -, but walk upright on two legs. First human ancestors to live on the savannah. Marked sexual dimorphism suggests male competition, but this is debated: if less dimorphic, more plausibly monogamous.

Austropithecus Skeleton of Lucy (early A. afarensis) vs modern woman:

2 MYA

• Homo habilis appears. Its face protrudes less than earlier hominids, but still retains many ape features. Has a brain volume of around 600 cm³

• Hominids start to use stone tools regularly, created by splitting pebbles

• Some hominids develop meat-rich diets as scavengers, the extra energy may have favoured the evolution of larger brains

• Also Homo ergaster, with a brain volume of up to 850 cm³, in Africa, not clearly distinct from Homo erectus (below)

(1.8 - 1.5 MYA

• Homo erectus (aka Pithecanthropus, maybe not ancestral to Homo sapiens) is found in Asia. First true hunter-gatherer ancestor, and also first to have migrated out of Africa in large numbers. It attains a brain size of around 1000 cm³

More complete timeline from http://humanorigins.si.edu :

Brain Size Timeline:

1.6 MYA

• Possible first sporadic use of fire suggested by discoloured sediments; clear evidence by 1MYA

• More complex Acheulean stone tools start to be produced and are the dominant technology until 100,000 years ago

(600,000 YA

• Homo Heidelbergensis (predecessor of Neanderthals) lives in Africa and Europe. Similar brain capacity to modern humans

500,000 YA

• Earliest evidence of purpose-built shelters - wooden huts - are known from sites near Chichibu, Japan

400,000 YA

• Early humans begin to hunt with spears

(230,000 YA

• Neanderthals appear and are found across Europe, from Britain in the west to Iran in the east, until they become extinct with the advent of modern humans 28,000 years ago

250,000-200,000 YA

• Our own species Homo sapiens appears on the scene - and shortly after begins to migrate across Asia and Europe (see also below). Oldest modern human remains are two skulls found in Ethiopia that date to this period. Average human brain volume is 1350 cm³

170,000 YA

• Mitochondrial Eve, the direct ancestor to all living people today, may have been living in Africa

150,000 YA??

• Speech and language likely; estimates of origin range from more than 500KYA to 50 KYA. 100,000-year-old shell jewelry suggests that that people develop complex speech and symbolism

50,000 YA to 100,000 YA

Main migration out of Africa by ancestors of modern humans

50,000 YA

• Human culture starts to change much more rapidly than before; people begin burying their dead ritually; create clothes from animal hides; and develop complex hunting techniques, such as pit-traps.

33,000 YA

• Oldest cave art. • Homo erectus dies out in Asia - replaced by modern man

15,000 YA

• Modern people reach the Americas

10,000 YA

• Agriculture develops and spread. First villages. Possible domestication of dogs

5,500 YA

• Bronze Age begins. Humans begin to smelt and work copper and tin, and use them in place of stone implements

5,000 YA

• Earliest known writing

4,000 to 3,500 BC

• Sumerians civilisation (Mesopotamia/Iraq)

Main source: John Pickrell, New Scientist, 25 August 2006 but see also the interactive site at the Smithsonian: http://humanorigins.si.edu