1. The Questions & the Best Current Answers
Human Evolution
The Questions & the Best Current Answers

2. The rules of science Hypotheses must be testable
Must be couched in previous knowledge (like a scientific theory).
What makes a theory scientific?
Why is the theory of evolution scientific?

3. Gravity What makes the theory of gravity scientific?
Can we prove a theory?
Are theories perfect?
Do they provide truth?
Should they be “believed” in?

4. What does the theory state?
Biological evolution = a shift over time in the proportion of organisms differing genetically in one or more traits.
Includes the following concepts
Natural selection
Genetic drift
Mutation
Gene flow
Extinction

5. What are the questions?
Where did all of the different living (today) species come from?
Have extinctions occurred in the past?
If the answers appear to be yes…
Then have humans evolved?

6. What are evolutionary hypotheses?
1)If life is static, no different fossil organisms should be found.
2)If life changes, fossils should be found of organisms that do not exist today.
We can disconfirm no. 1.
Does that mean we have “proven” two?
Does the fossil record disconfirm the ToE?
What evidence would disconfirm it?

7. What are evolutionary hypotheses about humans?
1)If humans did not evolve, then fossil forms in the past should be the same as today.
2)If humans did evolve, then different human-like forms should occur in the fossil record.
We can disconfirm no. 1?
But does this mean no. 2 is “proven?”
Does the fossil record disconfirm the ToE?
What evidence would disconfirm it?

8. Some other questions
Why do biologists think apes & humans share a common ancestor?
This is a very important question, because biologists & archaeologists expect that older human fossils should look more ape-like.

9. Some other hypotheses
1)If humans & apes do not share a common ancestor, they should not have similar DNA.
2)If humans & apes share a common ancestor, they should have DNA more similar than between humans & other mammals.
We can disconfirm no 1.
But does this mean no. 2 is “proven?”
Does the fossil record disconfirm the theory?
What evidence would disconfirm it?

10. More hypotheses
1)If humans & apes do not share a common ancestor, fossils should not look somewhat ape-like & somewhat human-like.
2)If humans & apes share a common ancestor, progressively older fossils should be more ape-like.
We can disconfirm no 1.
But does this mean no. 2 is “proven?”
Does the fossil record disconfirm the theory?
What evidence would disconfirm it?

11. In every single case…
Our conclusions are based on the disconfirmation of hypotheses.
It is important to base our conclusions on what we do not find.
The ToE is a scientific theory because it has never been disconfirmed following the rules of science.

12. When we look… At the modern biological world, what do we find?
At the fossil record, what do we find?
We find information that disconfirms stasis.
This is a carefully considered process that arrives at the “best current answer.”
It is not a personal opinion
It is not proof or truth

13. Scientists Scientists are people. People tend to be unscientific.
Scientists can be unscientific.
However, if you know what science is you should be able to tell whether or not hypotheses are disconfirmed, so science should stand on its own.

14. What do paleoanthropologists do?
They seek to test hypotheses like the ones we just considered.
Human geneticists look at modern genes in primates.
Paleoanthropologists study the fossil record.

15. What happens when fossils are found?
The paleoanthropologist must be careful about…
Recording information on the sediments in which the fossils were found.
Using PoA, PoS,& PoSIF
Comparative method must be used to answer…
How does a new fossil fit in with modern human skeletons and with other fossils that have been found?

16. Modern humans are… Fully bipedal & big brained.
So two very important questions are…
How big is the fossil specimen’s brain?
Do the legs & pelvis suggest bipedalism?
How might taphonomy matter here?

17. What’s in a name?
The most unscientific part of paleoanthropology is species naming.
Why?
What is a species?

18. A ring species

19. A new hominin skull is found…
Say it dates to 3.0 million years ago.
What species does it belong to?
What should we call it?
What is a fossil species?
These “species” may not be real groups, but we use the names to communicate.
Pretty sloppy & unscientific, but the fossils still exist, and can be used to test our hypotheses.

20. Why Africa?
The African Rift Valley is splitting along most of East Africa.
Results in long canyons & valleys where strata are exposed.

21. The Rift Valley
exploringafrica.matrix.msu.edu
images.encarta.msn.com

23.
images.encarta.msn.com

24. Summary Science is about falsification
Scientific theories have not yet been falsified, which is why they work.
There are testable hypotheses about human evolution.
Scientists are human & can be unscientific, like in hominin naming.
The African Rift Valley exposes sediments of the correct time period.

25. The Fossil Record

26. Humans are primates
Primates are mammals that share several physical characteristics.
Pentadactylism
3-D color, binocular, & peripheral vision
Prehensile, precise, & powerful gripping
Flexible limbs
Similar genes

27. Humans are primates,cont’d
We share behaviors with other primates.
Live in family groups
Use tools
Commit acts of violence
Intelligent problem solvers
images.encarta.msn.com
f.screensavers.com

28. Our lineage
Because of these similarities, it is hypothesized that apes & humans share a common ancestor.
This can be tested with the fossil record.
As the paleoanthropological record gets older, fossil hominids are more ape-like.
Hominin = a member of subfamily homininae, which includes humans & extinct close relatives
Hominid = a member of family hominidae, which includes apes & all hominins.

29. Sahelanthropus tchadensis
The earliest know Hominin.
Date 6 to 7 mya in Chad.
Foramen magnum points down.

30. Orrorin tugenesis
The next oldest, dates between 5 & 6 mya in Kenya (Tugen Hills).
Most of the early hominin fossils have been found in East Africa.

31. The Savanna Hypothesis: Why did Hominins become bipedal?
It is known that between roughly 7 & 4 mya grasslands expanded in East Africa (paleoenvironmental data)
This hypothesis states that this opening of grassland produced environments in which bipedalism evolved.
Literally, hominins came down out of the trees, and bipedalism was selected for.
Eventually these conditions, through natural selection cause the “ascent of man” into a bipedal walker.
Test this hypothesis using Sahelanthropus and Orrorin fossils…

32. Why is this cartoon funny?
Because the savanna hypothesis has been falsified.
Scientists, being people, really believed in this hypothesis.
Alas, being a scientist means you must set your beliefs aside when your favorite hypothesis is disconfirmed.
The Orrorin and Sahelanthropus fossils disconfirm the savanna hypothesis.
This is the case because both forms were fully bipedal prior to the opening of savanna.

33. Moving forward in time…
The fossil record is patchy & earlier periods have limited evidence, yet it does offer evidence of bipedalism & human-like teeth.
The record dating to later than 4 mya, however, is more complete.
How does site discovery & the preservation equation matter here?
P = MCDST
Survey, excavation, recovery

34. Diversity in the fossil humans at 4 mya
What do paleoanthropologists mean by “human?”
They are not speaking only of modern humans.
They mean fossil-human ancestors & their cousins that became extinct.
So the Orrorin fossils are human.
Remember, evolution is a tree, some branches of which go extinct, some which continue to evolve.

35. The Australopithecines
Members of the genus Australopithecus
The only fossils known between Orrorin & Australopithecus are:
Ardipithecus ramidus (5.6 – 4.3 mya)
Poorly known from Ethiopia.
Only fragments, but some are mandibles w/ teeth.
Estimated brain size is 400 – 450 cc.

36. Lucy Lucy is the most complete skeleton of an early hominid.
Found in Hadar, Ethiopia (1974).
Australopithecus afarensis
Found in many areas of East Africa.
4.0 – 3.0 mya.
Lucy was a small-brained biped.
Small brain 380 – 500 cc
Lucy was 3’6” tall 50 lb
Dates to 3.2 mya

37. The Australopithecines, cont’d
There appear to have been several species of Australopithecus.
Some of these are likely to have been in the human line.
There are a few types, however…

38. Cousins? The robust australopithecines 3 – 1.5 mya
Australopithecus aethiopicus
Australopithecus boisei
Australopithecus robustus
Brain size around 500 cc
Sometimes “Australopithecus” is replaced with “Paranthropus.”

39. Robust Australopithicus
Homo habilis
1.5 mya
Robust Australopithicus
extinct
Australopithecus africanus
2 mya
Australopithecus afarensis
4 mya

40. What’s different about Homo habilis?
Homo habilis has a bigger brain
600 – 800 cc
Is missing a sagittal crest
Has a face that is less prognathic
Is missing a diastema
A smaller zygomatic arch
Used stone tools?
PoA matters here, why?

41. Robust Australopithecus
Modern human
Robust Australopithecus
anthro.palomar.edu
Chimpanzee

42. Early hominins: summary
There are fossils dating back to roughly 7mya that are hominin.
They are bipedal
They are intermediate between apes & humans in shape & size
By 2 mya brains in hominins are larger and stone tools appear.
Archaeology really begins with stone tools.

43. The Earliest Hominins
A picture review

45. Sahelanthropus

46. A. afarensis
4 – 3 mya
East Africa

47. Laetoli footprints, Tanzania: A. afarensis

48. A. robustus/boisei/ aethiiopicus 3 – 1.5 mya East & South Africa
Modern