Transcript Biology 4.34 Modern View

Hominin Evolution -
Human Evolution
• Aims:
• Must be able to outline the main stages of Human
evolution.
• Should be able to compare and contrast the main
hypotheses for Human evolution.
• Could be able to discuss the current and possible
future evolutionary trends.
Human Evolution: a 1960s View
•
The illustration below was in common usage in the popular press
30 years ago to represent the linear progression from a primitive
ape-like ancestor to modern humans.
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It is still used in advertising as a visual metaphor for the “idea” of evolution.
Evolving lineage with the accumulation of gradual genetic changes under the influence of natural selection
Human Evolution: a 1960s View
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Predictions According to the
Linear Progression Model
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The fossil record should
consistently show smooth intergradations from one species to
the next.
• The Actual Evidence Observed in
the Fossil Record
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Few smooth inter-gradations from
one species to the next
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Species tend to appear suddenly in
the fossil record
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The species linger for varying but often
very extended periods of time in the
fossil record
•
The species disappear as suddenly
as they arrived
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They are replaced by other species
which might or might not be closely
related to them.
Human Evolution: a Modern View
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The 1st radiation: Early bipedal apes –
including the australopithecines.
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The 2nd radiation: Involved genus
Paranthropus, group of species that
exploited low-grade vegetable food sources
(nuts, root tubers and seeds) resulting in
(megadont) species with very large teeth.
•
3rd radiation: Genus Homo, with the
habilines and erectines developing a larger
brain, diversifying, and dispersing from
Africa to other parts of the Old World.
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Last radiation: does not involve major
evolutionary divergence, reflects dispersal
of modern humans worldwide.
Megadonts
African apes
Early
Bipedal
Apes
Diversity
Source: Ian Tattersall, The Fossil Trail, Oxford University Press (1995)
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Time (millions of years)
A modern view of human evolution
maintains that it has occurred as a
series of adaptive radiations.
Human Evolution Timeline
0
Homo sapiens
Chimpanzees (Pan)
H. heidelbergensis
H. neanderthalensis
1
H. erectus
H. floresiensis
Paranthropus boisei
H. antecessor
P. robustus
H. habilis
2
H. ergaster
Au. garhi
Millions of Years
H. rudolfensis
P. aethiopicus
3
Kenyanthropus platyops
Au. africanus
Australopithecus bahrelghazali
4
5
6
7
Australopithecus anamensis
Archaic and Modern Humans: Rapid advances in brain
size; suite of new behaviors. Anatomically modern humans
emerge from one of the many regional variants.
Erectines: Body height of modern proportions. Increasing
brain volume. Sophisticated tools are manufactured and
used to kill and process small sized game.
Australopithecines: Possessed a gracile body form and
were probably opportunistic omnivores/scavengers.
Habilines: Brain enlargement, first recognizable stone
tools, body remains small/slight.
8
Paranthropines: Early hominids specialized for eating a
bulky, low-grade vegetarian diet. Developed powerful
chewing muscles and a generally robust skull.
Early Hominids: Brain size similar to modern chimpanzees,
body remains small/slight. Hominid status may be in question.
Au. afarensis
Ardipithecus ramidus
Orrorin tugenensis
Sahelanthropus tchadensis
The Origin of Modern Humans
•
There are two theories accounting for the origin of anatomically
modern humans (Homo sapiens):
Multi-regional Hypothesis
Replacement Hypothesis
(Out of Africa / Eve Hypotheses)
Present
Modern
Homo sapiens
Archaic
Homo sapiens
Extinction
0.5 mya
Gene flow
Homo erectus
1.0 mya
African origin
African origin
The Replacement Hypothesis
• Also known as the “Out of
Africa Hypothesis” and “Eve
Hypothesis”.
Modern
Homo sapiens
Present
• All modern humans can trace
their evolutionary heritage to a
single woman via changes in
mitochondrial DNA.
Archaic
Homo sapiens
0.5 mya
• This woman, 'Eve', lived about
200 000 years ago in Africa.
Homo erectus
• The descendants of this
population of modern humans
dispersed throughout the rest
of the world, displacing all other
human populations in existence
at the time.
1.0 mya
African origin
The Multiregional Hypothesis
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This theory is based largely on
the fossil evidence and the
anatomical characteristics of
modern populations.
Modern
Homo sapiens
Present
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The mitochondrial DNA data
can be interpreted in a variety
of ways, one of which supports
a multi-regional origin of
modern humans.
Archaic
Homo sapiens
0.5 mya
Modern human populations
can be traced back in the fossil
record to about 1 million years
ago when Homo erectus first
left Africa.
Homo erectus
1.0 mya
African origin
•
Continuous gene flow occurred
between regional populations.
Dispersal of Modern Humans
• This map shows a probable
origin and dispersal of
modern humans throughout
the world.
• An African origin is almost
Skuhl
101 00081 000 ya
certain, with south eastern
Africa being the most likely
region.
Qafzeh
120 00092 000 ya
Omo
195 000 ya
Probable area of origin
for modern humans
some 200 000 years ago
Border Cave
115 000-62 000 ya
Klasies River Mouth
120 000-84 000 ya
ya = years ago
Dispersal of Modern Humans
The first modern humans
appear in Europe 40 000 35 000 years ago
Humans travel to
the Americas
between 30 00015 000 years ago
Cro-Magnon
30 000 ya
Earliest dating in East
Asia is 67 000 years ago
in southern China
Skuhl
101 000 81 000 ya
Probable area of
origin for modern
humans some
200 000 years ago
Qafzeh
120 000 - 92 000 ya
Omo
195 000 ya
Polynesia populated
progressively 4500 700 years ago
Malakunanja II
50 000 ya
Lake Mungo
31 000 ya
Border Cave
115 000 - 62 000 ya
Klasies River Mouth
120 000 - 84 000 ya
Australia was first
occupied at least
50 000 years ago
Human Biological Evolution
• Natural selection has acted over generations on
inherited phenotypes and as a result changes have
occurred in reference to survival and reproduction.
• Evidence of this can be seen in:
Variation in height, weight,
• Physical traits
skin colour, hair texture etc
Variation in blood type,
• Biochemical traits
enzyme concentration,
hormones etc
Variation in tolerance to
• Physiological traits
foods, temperature,
metabolism etc
Activity
Answer the questions on pages 383 to 391 and
395/6 in the Biozone books.
Present and Future Evolution
• Over the next few thousand years, human evolution will be influenced by
a number of new factors:
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Natural selection pressures may select for beauty, intelligence, body
symmetry, disease resistance, and tolerance to pollutants and
electromagnetic radiation.
Genetic engineering may introduce new and possibly novel genes to
add new traits.
Gene therapy may replace, remove, or turn off unwanted, perhaps
harmful, genes.
Nanotechnology may provide a means to tinker with anatomy and
physiology at the cellular level to repair or enhance function.
Prosthetic enhancements and implants (although not inherited) may
extend human performance beyond its present, natural range.
Activity
Answer the questions on page 400 in the Biozone books.