Lecture 1.1: Human History—The first four billion years

Human History- The first Four billion Years

• We live in a very weird moment in the history of our species and planet

  • Only 8 generations (out of 10,000 of anatomically modern humans) have understood how we got here

  • Discovery of evolution was a momentous event in human history

• Studying evolutionary psychology involves a mindset shift to evolutionary time scales

• Darwin in the 1800s was liberated to think about evoultion by research showing how old the planet is

• People thought the planet was 6000 years old truth is it was 4.5 billion years

What time scales should we use

Billionaire time scales are unfathomable; use 24-hour analogy:

• Earth forms (4.5 billion years ago) → beginning of day

• Noon → ~2 billion years ago.

• Midnight → present moment.

What is the time scale of our world? 

• 4.5 billion years: Earth formed and than for while we had evolving atmosphere (12am)

• 3.5 billion years: life emerges, simple bacteria for 12 hours (5:30am)

  • One small thing is gradually happening for a long period of time: Photosynthesis 

  • Photosynthesis produced oxygen → changed oceans & atmosphere ( redies the environment for multicellular organisms 

• Multicellular organisms 1bya early evening 

• 600 mya (9pm)  Cambrian explosion : major body plans emerge

  • Fish, land plants, trees (500MYA): 9–10 PM

• Animals on land, insects: after 10 PM.

• Dinosaurs: appear ~11 PM.

  • Existed 135 million years (~40 min).

  • Extinct 65 million years ago (~20 min before midnight).

• Flowers, primates: appear only after dinosaurs gone.

• Humans: just 4 seconds before midnight (200kya)

What happened 6 million years ago in human and chimpanzee evolution, and how did chimpanzee speciation occur?

6 mya: We last shared a common ancestor, which is our last closest living relative 

• Both us and chimpanzees descended from our common ancestor and since then we have gone through our own evolutions

  • Chimps are cousins, not uncles/parents.

  • Both chimps and humans evolved since.

• 2.5mya, two groups of proto-chimpanzees got separated by the congo river, they remained separated and both followed their own evolution

  • Separated groups evolved into:

    • Pan troglodytes (regular chimpanzee).

    • Pan bonobo (bonobo chimpanzee).

  • Speciation occurs when populations are separated long enough.

Proto-Humans: Which was the first one 

Australopithecus

• First fully bipedal ancestor

• 200,000 great grandpa (4.5-2.4MYA)

• Bipedal allowed more height and allowed us too see further over grass horizon

  • It allowed cooling, seeing, gathering and tool use

• Freed our hands which allowed us to gather

• Used found tools (not fashioned).

• Brain size ~⅓ of modern human comparable to what a chimpanzee has now.

• most importantly it allowed us to use tools did not make tools but used tools

Proto-Humans: Which was the second one 

Homo habilis (“handy man”)

• First in Genus homo, that is the genus we are part of

• They did make their own tools and had 1/2 of our current brain size

• eventually evolved into upright man

Proto-Humans: Which was the third one 

Homo erectus (“upright man”)

• Tools more complex.

• Brain size ~⅔ of modern human.

• First to migrate out of Africa (into Middle East, Asia, possibly Europe).

• first of our species to venture out of africa

• prior to this we were all in africa but many of us now migrated

Proto-Humans: Our almost human ancestors

Brain capacity almost the same as ours

• 200,000–800,000 years ago.

• Brain size almost modern human.

• Split (300,000–600,000 years ago) → speciation.

• Homo heidelbergensis was our shared common ancestor with Homo neanderthalensis

What was the speciation of Homo heidelbergensis, and how did Neanderthals and Homo sapiens differ?

• Homo heidelbergensis split into two populations:

  • One in Africa.

  • One that moved into Europe and evolved into Homo neanderthalensis.

• 700,000 years ago: Sahara was green grassland (during Ice Age).

• Range: South Africa → Middle East.

• End of Ice Age → Sahara became desert causing it to be intraversible which caused seperation.

• Populations separated:

  • Europe → Homo neanderthalensis (Neanderthals).

  • Africa → Homo sapiens (us).

Neanderthals vs Humans

• Range: Europe only (blocked by desert).

• Larger cranial capacity than humans.

• Coexisted with humans after Homo sapiens migrated out of Africa.

• Neanderthals became extinct ~35,000 years ago.

Homo sapiens

• Modern humans evolved ~200,000 years ago.

• Left Africa ~80–60KYA years ago (1 second before midnight).