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Human Evolution

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It is not a personal opinion. It is not proof or ... images.encarta.msn.com. Our lineage ... The record dating to later than 4 mya, however, is more complete. ... – PowerPoint PPT presentation

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Title: Human Evolution


1
Human Evolution
www.micro.utexas.edu
  • 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 specimens brain?
  • Do the legs pelvis suggest bipedalism?
  • How might taphonomy matter here?

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

18
A ring species
www.pbs.org/wgbh/evolution
www.virtuallaboratory.net
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
22
www.geology.iupui.edu
23
www.ipoaa.com/images
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
www.bluetang.org
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,contd
  • 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.

www.skulls-skeletons.com
Hominid a member of family hominidae, which
includes apes all hominins.
Hominin a member of subfamily homininae, which
includes humans extinct close relatives
29
Sahelanthropus tchadensis
  • The earliest know Hominin.
  • Date 6 to 7 mya in Chad.
  • Foramen magnum points down.

www.talkorigins.org
www.bradshawfoundation.com
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.

www.cnrs.fr/cw
www.ipoaa.com/images
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 36 tall 50 lb
  • Dates to 3.2 mya

37
The Australopithecines, contd
  • 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.

www.portalciencia.net/
39
Homo habilis
1.5 mya
Robust Australopithicus extinct
Australopithecus africanus
2 mya
Australopithecus afarensis
4 mya
www.portalciencia.net/
www.skullsunlimited.com
40
Whats 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
Australopithecus
Modern human
www.peteducation.com
www.carolina.com
Robust Australopithecus
anthro.palomar.edu
Chimpanzee
www.talkorigins.org
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

44
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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
49
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