1. Human Evolution
GO BACK.
WE MESSED UP
EVERYTHING!

2. Human Evolution Humans are Primates Human Ancestry Hominins
Misconceptions About Human Evolution

3. What are Primates?

4. Primate Characteristics
Hands
Dexterous—fine motor control
Nails—not claws
Sensitive
Eyes in Front of Face
Loose Shoulder Joint
Parental Care
Why?
: grasp branches
: binocular vision = good depth perception
: swing from branches
: protect helpless infants
Adaptations for arboreal existence

5. Human Evolution Humans are Primates Human Ancestry Hominins
Misconceptions About Human Evolution

6. When did Humans and Chimps Diverge?
Most recent common ancestor: 5-6 Mya

7. Where Did Humans Evolve?
Location?
Evidence?
Fossils
Genetic evidence
Africa

8. Human Evolution Humans are Primates Human Ancestry Hominins
Misconceptions About Human Evolution

9. What are Hominins?
Hominins—group consisting of modern humans, extinct human species and all our immediate ancestors
Species to know:
Ardipithecus ramidus
Australopithecus
A. afarensis
A. africanus
Homo
H. habilis
H. erectus
H. neanderthalensis
H. sapiens

10. Hominin Evolutionary Tree
Ardipethicus

11. Ardipithecus ramidus 4.4 Mya Small brain 300-350 cm3
Slightly smaller than chimp

12. Hominin Evolutionary Tree
Australopithecus

13. Australopithecus Arose 4.1 Mya 2 species to know What do you notice?
Australopithecus afarensis (“Lucy”)
Australopithecus africanus
What do you notice?
Small brain
cm3
Slightly larger than chimp
Short: m
Bipedal: walk on 2 legs
How do we know Australopithecus was bipedal?
Lucy

14. Evidence of Bipedalism: Fossilized Footprints
What happened? What do you see?
3.6 Mya in Laetoli, Tanzania, two Australopithicines walked through wet volcanic ash. When nearby volcano erupted again, layers of ash covered and preserved footprints.
How is this evidence of bipedalism?
Footprints made by 2 limbs, not 4

15. Evidence of Bipedalism: Foot
What do you notice?
Other primates
Opposable big toe
Big toe not in line with other toes
Long toes
Humans
Non-opposable big toe
Big toe in line with other toes
Short toes
Why the differences? How is this evidence of bipedalism?

16. Evidence of Bipedalism: Foot
Other primates
Live in trees
Grasping foot for grabbing objects
Humans
Live on ground
Platform foot for walking

17. Evidence of Bipedalism: Foot
Australopithecus foot
What do you notice?
Looks like human foot
Platform foot for walking on ground

18. Evidence of Bipedalism: Pelvis, Femur, Knee Bones
What do you notice about legs?
Chimpanzee
Legs straight
Human & Australopithecus
Knock-kneed (thighs aim inward)
Why are our legs like this?
When we walk, briefly stand on 1 foot
Knock-kneed keeps foot under center of gravity, aiding balance
n-characteristics/walking
Australopithecus?
Same as modern humans

19. Evidence of Bipedalism: Foramen Magnum
Hole in skull through which spinal cord enters
What do you notice?
Chimpanzee at back of skull
Human, Australopithecus at bottom of skull
Why? How is this evidence of bipedalism?

20. Evidence of Bipedalism: Foramen Magnum
Bottom of skull = upright posture (bipedal)
Back of skull = quadrupedal
What happens when human tries to be quadrupedal?

21. Advantages of Bipedalism
Frees hands: carry things
Gather food
Parental care
Elevates eyes
See predators & prey better

22. Hominin Evolutionary Tree
Homo

23. Homo Arose 2.5 Mya 4 species to know What do you notice? Bigger brain
Homo habilis: 1st tools
Homo erectus: 1st to migrate out of Africa
Homo neanderthalensis: sometimes classified as subspecies of modern humans
Homo sapiens: last 100 ky
What do you notice?
Bigger brain
cm3
Taller

24. Human Evolution Humans are Primates Human Ancestry Hominins
Misconceptions About Human Evolution

25. Misconceptions About Human Evolution
Humans evolved from chimps
If humans evolved from chimps, why are chimps still here?
Human evolutionary tree is a ladder
Upright posture and big brains evolved simultaneously

26. Humans evolved from chimps;
What’s wrong with this idea?
Humans did not evolve from chimps; rather, they share a common ancestor

27. If humans evolved from chimps, why are chimps still here?
A new species can arise even while the parent species persists
This question assumes that we are somehow “improved” over chimps, so they shouldn’t be here anymore; this is a misconception: each species is well adapted for its lifestyle

28. Human evolutionary tree is a ladder
Each species improves upon and replaces the one before it
What’s wrong with this idea?

29. What does the human evolutionary tree look like?
Shrub with many branches
At most times, many different hominin species lived simultaneously
In many cases, new hominin species arose while the parent species persisted

30. Upright posture and big brains evolved simultaneously
What’s wrong with this idea?
Upright posture evolved 1st in Australopithecus
Big brains evolved later in Homo

31. How Did We Get Our Big Brains?
How has hominin brain size changed over time?

32. A Clue in Growth & Development
What do you notice?
Fetus skulls
Human and chimp look similar
Start large brain case & small jaw
Brain case : jaw proportion similar
Adult skulls
Skulls look different
Chimp has smaller brain case, larger jaw
How can this help explain big brains in humans?

33. Large Brains Explained
Grid on fetal skulls allows us to see relative growth of different parts of skull
What do you notice?
In both, jaw grows faster than brain case
Adolescent chimp similar proportions to adult human
Chimp continues to develop
So, to get a bigger brain …
Slow down the developmental process so human skull can grow over a longer time … then it and the brain will get bigger