The Story of Human Evolution

From Primates to Homo sapiens sapiens

The Myth of the Biggest and Bestest “survival of the fittest”

Our cultural problem

Stephen Jay Gould

history of biological life = “proliferation of enormously varied designs subsequently restricted to a few highly successful, but imperfect, forms”

“Our world is not an optimal place fine-tuned by omnipotent forces of selection. It is a quirky mass of imperfections, working well enough (often admirably); a jury-rigged set of adaptations, built of curious parts made available by past histories in different contexts.”

Considering Evolution

Natural Selection: an evolutionary process through which factors

in the environment exert pressure that favors some individuals over others to reproduce the next generation of the group

this pressure acts on phenotype (genes plus environment), not genotype (DNA, genetic makeup)

Never exact match between phenotype and genotype

Never exact fit between organism and environment: dynamism

Biological plasticity of individuals

Fig 8-2

Note: there are prosimians (eg lemurs), new world monkeys (eg spider monkey,Old world monkeys (eg baboons), and apes.

Apes include gibbons, orangutans, chimps, bonobos, gorillas and humans. 99% of human DNA shared with chimps (study in Nature, 8.31.2005)

Primate Tendencies

Grasping and opposable thumbs Smell sight mouth hand brain complexity increases parental investment increases Sociality increases

Snarling mandrill

Gorilla familygibbon

humans

chimp

Primate Social Behavior

Wide range of social behaviors and types of social organization for different species—a few examples follow Male led (chimps),

female led (bonobos), Savanna baboons—

highly complex multi male and female troops

Only ape that is monogamous—gibbon

Apes that display wide range of sexual behavior—bonobos

Overview of Hominid Evolution

Australopithecines (Lucy) 5-2 million years ago (mya) Gracile Robust

Homo habilis (3-2 mya) Homo erectus (1.5 – 0.4 mya, or ?12,000ya) Homo sapiens (.02 mya, 200k-present)

Homo sapiens neanderthalensis 60k Homo sapiens sapiens (dif places different times)

200,000k

Key Ideas

Feedback and inadvertency Bipedalism Brain Size/complexity Tools, Language and Culture

Shifts in lifestyles/diets

Types of evolutionary change Graduated Punctuated Equilibrium

Fig 9-5

Chimp Skeleton Human skeleton

Characteristics of Australopithecines

General Characteristics Skeleton: Bipedal, not fully upright Brain only slightly bigger than a chimp’s. Smaller canines than a chimp, bigger molars Hands: precision and power grip. Likely savanna adaptation—likely vegetarian

Robustus has extreme savanna adaptation Recent debate re: degree of bipedality, habitat

type

The skeleton of Lucy, notice the bipedality along with a relatively small cranium andchimp-like skull

Fig 9-8

Australopithecus sites in Africa

On Bipedalism: Australopithecines take steps… Disadvantages?

visible to predators exposed underbelly slow

Advantages? Man the hunter? (NO!) Woman the food

carrier Infant carry

Artist’s rendering of A. africanus(interesting way in which racial ideas intervene)

Why Be Bipedal?

Advantages, con’d Efficient food

procurement? See farther? Efficient long distance

travel? Cool brain? All of the above?

Artist’s rendering of A. africanus

Effect of Bipedality: inadvertency in human evolution, 2 examples

1. Hands are free tool use increasing tool use

leads to increasing brain size and complexity

2. the birth canal problem and its consequence (evolution at work)

Fig 9-6

Pelvis structure of Humans and Chimps

From Australopithecus to Homo: moving towards culture

Homo habilis (the handy man!)—(3-2 mya) Brain

larger: 650 cm2

area of skull indicates language

Body more gracile

Robust and Habilis Hung Out

Robust australopithecines (A. boisei) and H. habilis co-existed for at least 1/2 million years

What happened? Why did Australopithecines die out? Competitive exclusion? Niche divergence? (natural selection is

environment specific)

Homo Erectus

Lived 1.5 to .4 mya 1 mya as single spp. Example of punctuated

equilibrium Significant increase in

brain size: 850-1200 Fully erect/bipedal

Homo Erectus Lifestyle, con’d First use of fire

cook heat protection against predators thaw out carcasses

Evidence of “culture” or symbolic activity complexity of tools cooperative hunting red ochre

Illustration of an Erectus cooperative elephant hunt

Homo Erectus lifestyle, con’d

Migration out of Africa, first time in H. history

Modern Humans, Early Homo sapiens sapiens

Timing of first evidence Africa: more than

100,000 ya Asia: 60,000 ya Europe: 35,000 ya Australia: 40,000 ya Americas: 20,000 ya

Early Modern H. s. s.

Cultural changes Art (Cro Magnon) tools

standardization distinct sets for

distinct areas indicating cultural diversity

Neanderthals

Debate over where they belong in evolutionary story

The “cave man” …with a large brain Robust skeletons Latest research

Recent Finding from Indonesia

2004: Tiny Homo floresiensis, 3 feet tall, resembling H. erectus in some ways, but found with evidence of highly developed culture, boats, etc Endemic island dwarfing (happens to a lot of other

large mammals on islands) Small brain, lots of smartness… Co-habited earth with modern humans—these finds

are from 12-18 k years ago Cultural groups in the area have stories/legends about

“small people” Most recent debates: some researchers argue that

these are just small modern humans

Theories of the Origins of Modern Humans Two competing theories:

Multiregional Replacement/Out of Africa

Multiregional/Local Continuity Theory evidence

apparently intermediate fossil forms between H. erectus and modern humans in each location (Africa, Asia, Europe)

Theories of the Origins of Modern Humans, con’d Replacement/Out of Africa-Mitochondrial Eve

Theory evidence

earliest H. sapiens sapiens found in Africa Mitochondrial and nuclear DNA

all humans closely related, genes diverged from single recent African origin, at about 100 kya

Neanderthal mtDNA is not more similar to European than any other

The Most Logical Theory: A Mix of the two Independent evolution unlikely 3x Interbreeding/gene flow likely, migration and

movement all along The human thing

migration interbreeding

Implications for understanding race

Questions to ask about your skulls

What species is it? When did it live? What are its key skeletal and other (?culture,

etc) features Why is it significant? Where does it fit on evolutionary tree leading

to Homo sapiens sapiens