Title: Human Evolution
1Human Evolution
www.micro.utexas.edu
- The Questions the Best Current Answers
2The 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?
3Gravity
- What makes the theory of gravity scientific?
- Can we prove a theory?
- Are theories perfect?
- Do they provide truth?
- Should they be believed in?
4What 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
5What 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?
6What 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?
7What 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?
8Some 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.
9Some 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?
10More 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?
11In 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.
12When 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
13Scientists
- 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.
14What 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.
15What 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?
16Modern 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?
17Whats in a name?
- The most unscientific part of paleoanthropology
is species naming. - Why?
- What is a species?
18A ring species
www.pbs.org/wgbh/evolution
www.virtuallaboratory.net
19A 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.
20Why Africa?
- The African Rift Valley is splitting along most
of East Africa. - Results in long canyons valleys where strata
are exposed.
21The Rift Valley
exploringafrica.matrix.msu.edu
images.encarta.msn.com
22www.geology.iupui.edu
23www.ipoaa.com/images
images.encarta.msn.com
24Summary
- 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.
25The Fossil Record
www.bluetang.org
26Humans 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
27Humans are primates,contd
- We share behaviors with other primates.
- Live in family groups
- Use tools
- Commit acts of violence
- Intelligent problem solvers
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28Our 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
29Sahelanthropus tchadensis
- The earliest know Hominin.
- Date 6 to 7 mya in Chad.
- Foramen magnum points down.
www.talkorigins.org
www.bradshawfoundation.com
30Orrorin 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
31The 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
32Why 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.
33Moving 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
34Diversity 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.
35The 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.
36Lucy
- 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
37The 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
38Cousins?
- 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/
39Homo habilis
1.5 mya
Robust Australopithicus extinct
Australopithecus africanus
2 mya
Australopithecus afarensis
4 mya
www.portalciencia.net/
www.skullsunlimited.com
40Whats 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?
41Australopithecus
Modern human
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www.carolina.com
Robust Australopithecus
anthro.palomar.edu
Chimpanzee
www.talkorigins.org
42Early 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.
43The Earliest Hominins
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45Sahelanthropus
46A. afarensis 4 3 mya East Africa
47Laetoli footprints, Tanzania A. afarensis
48A. robustus/boisei/ aethiiopicus 3 1.5
mya East South Africa
Modern
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