human evolution 🧍‍♂️

• Organisms with common features are likely to have a more recent common ancestor, 7 - 8 mya. 
• Sample size of hominin fossils is very small:

  • Inferences drawn on a small sample are difficult 
  • Fossils may not have come from where they are found 
  • Two species may appear to live side by side but actually don’t, like gorilla and chimps 
• During human evolution there is overall climatic cooling, but with increasing fluctuations. The climate is also becoming more seasonal and drier. 
• 1. Hominin origins 
  2. Bipedal 
  3. First stone toolmaking 
  4. Onset of long endurance mobility 
  5. Onset of rapid brain growth 
  6. Expansion of symbolic expression, innovation and cultural diversity. 
• Savanna hypothesis:

  • Climate got colder over last 10 my 
  • Uplift of east Africa that made it drier 
  • Spread of savanna grassland 
  • Reduction of tree cover meant it was better to run fast and spot predators than climb a tree to safety 
  • Bipedalism means that the hands become free for holding, carrying or using tools 
  • Increased use of tools then drove increased brains 
• Bipedalism:

  • Seen 6 -7 mya 
  • Allowed reaching and carrying of food, better vision and improve long distance running 
  • Legs have become longer 
  • Arms are shorter 
  • Big toe aligned with others 
• Savanna hypothesis:

  • Faunal fossil remains
  • Ocean sediment climate change evidence 
  • Matching timing of climate change with appearance of new species 
• Evolution and climate change:

  • If human adaptations were due to climate change on savanna 
  • Those adaptations should be unique to that environment 
  • However fossils show other features that do not correlate with the savanna environment 

   

   
• Pulsed climate variability hypothesis:

  • Characteristics develop as a response to selection pressures in savanna 
  • However savanna adapted humans were also found in woodland and other habitats 
  • Skeletons were adaptable and able to survive in a range of environments 
  • It was climate variability that drove evolution, hominins that could adapt to changing climates were the ones that survived. 
• Climate change in Kenya:

  • Environmental variability linked to extinction of large mammals that were also specialised 
  • Ancient lake level changed frequently 
  • Volcanic eruptions also covered the area, killing plants and changing climate 
  • Human fossils found throughout hillside and did no go extinct 
• Stone tools:

  • First found from 3.3 mya 
  • Simple tools made by stone on stone fracturing 
  • Sharp flakes for cutting 
  • Stones for pounding and crushing 
  • Allowed access to larger variety of food 
  • Carrying tools over distance to new locations, 
  • Became dependant on stone tools 
• Lucy:

  • Lived 3.16 mya 
  • Humanlike hip bones and knees, 
  • long apelike arms with long grasping fingers, 
  • flexible feet for walking 
  • Gave the ability to move between habitats 
• Expanding of early homo world:

  • From 1.85 mya 
  • Genus homo was found in lots of locations in Asia 
  • Others were found in the far north 
• Climate change and migration:

  • 2 mya homo ergaster migrated out of Africa into Asia 
  • Fits with the appearance of homo erectus in Asia by 1 mya as erectus evolved from ergaster 
  • Discovery of homo floresensis in Indonesia shoes that there were other migrations out of Africa before homo sapiens 
  • During glacials the climate in Sinai and Sahara was cold and dry so were impassible 
  • Interglacials the climate warmed and was wetter allowing migration out of Africa 
• Brains:

  • Larger brains allowed for better processing and storage of info, to plan ahead and solve problems 
  • Create more complicated tools, adapt to changing diets and share resources 
  • Larger brain gives increase the number of habitable environments 
• Neanderthals:

  • Limited to Europe and eastern middle east 
  • During most recent ice age 
  • Lived in colder places 
  • Short and stocky 
  • Large noses 
  • Large nose to warm air 
  • Barrel shaped chest 
  • Long low thick skull but had a large brain 
• Neanderthals:

  • During cold periods - hunted reindeer 
  • During warmer periods - hunted red deer 
  • During very cold periods - shifted range southwards to warmer locations 
• Homosapien:

  • First evidence from Africa 300000 years ago 
  • A few in middle east 180000 years ago 
  • More widespread migration 70000 - 100000 years ago 
  • Specialist use of tools, communication and social networks 
• Neanderthals vs homosapien:

  • Sapiens - very specialised tools, social networks and exchange of good over long distances. Used symbols to communicate 
  • Neanderthals - less specialised tools, no exchange of materials 
  • Modern humans expanded their range to America and Asia 
  • Neanderthals went extinct 
  • Maybe due to lack of adaptability 
• Evaluating evolution:

  • Lack of fossil evidence on land 
  • Tree dwelling animals dissolved by acidic soil 
  • Some debate over classification of bones 
  • Little evidence of the split of hominin from great apes 
  • Hard to say when tool use started 
  • Evidence of migration into Asia has been destroyed by sea level rise at end of glacial 
• Possible that interbreeding between different hominid species played a role in evolution. Maybe not linear but a web.