Evolution
Genetic changes in populations that over generations
leading to new types of organisms.
……. Study & Master Life Sciences
(Preethlall, et al, 2006)
Sourrce:http://evolution.berkeley.edu
Life has a history
It has changed over time
Different species share common ancestors.
Evolutionary change and evolutionary relationships are
represented in "family trees,"
• This knowledge affects biological classification
• Information on some specific events in the history of life:
human evolution and the origin of life.
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EVOLUTION
HYPOTHESIS OR
THEORY?
HYPOTHESIS
▪ Provides a proposed solution to a problem
of a specific phenomenon, based on
evidence and observation.
▪ Tested in series of experiment/observations
▪ Can be rejected or accepted
Theory
• An explanation which can be supported by facts, laws
and tested hypotheses.
• Based on evidence and tested and confirmed by
independent
groups of scientists
• It develops and changes as new evidence is discovered.
• Examples:
– Heliocentric theory (the Earth revolves around the sun)
– Atomic theory (structure of matter)
– Most scientists accept that the theory of evolution has
the same factual basis as the two theories above.
Evolution as Theory and Fact
• Confusion sometimes arises as to
whether Evolution is a theory or a fact.
Actually it is both!
Rodin’s “The
Thinker”
• The theory of Evolution deals with how
Evolution happens. Our understanding
of this process is always changing.
• Evolution is also a fact as there is a
huge amount of indisputable evidence
for its occurrence.
Charles Darwin (1809 – 1882)
Develop the Theory of Evolution by Natural
selection.
Darwin's 5-year voyage around the world in
the HMS Beagle, collecting specimens and
keeping notes of plants, animals seen and
geography of countries visited .
Publication of Darwin's
On the Origin of the
Species in 1859.
Evidence for evolution
•Modification by descent
•Biogeography
•Fossil record
•Genetics
Evidence: Modification by Descent
Plant and animal groups were
modified to adapt their
environments
Forelimb
Hind Limb
Humerus
(upper arm)
Femur
(thigh)
Ulna
Fibula
Radius
• The pentadactyl
(5 digit) limb found in most
vertebrates has the same
general bone structure.
Carpals
(wrist)
Tibia
Tarsals
(ankle)
Metacarpals
(palm)
Metatarsals
(sole)
Phalanges
(fingers)
Phalanges
(toes)
Note that forelimbs and hind limbs
have different names for
equivalent bones.
Homologous Structures
• In many vertebrates, the basic
pentadactyl limb has been
highly modified to serve
specialized locomotory
functions.
Bird's wing
• Such homologies also indicate
Dog's
front
leg
adaptive radiation, as the
basic limb plan has been
adapted to meet the needs of
different niches.
• The same pattern of bones
comprising the pentadactyl
limb can be seen on each of
these examples.
Mole's
forelimb
Bat's wing
Seal'
s
flippe
r
Human arm
HOMOLOGOUS STRUCTURES: same basic plan
different functions
Had common ancestor which became adapted to
live in different environments
ADAPTIVE RADIATION – DIVERGENT EVOLUTION
Species A
Species B
Species C
Species adapted to function in
different environments
Ancestral species
Species D
Analogous Structures
• Not all similarities between species are
inherited from a common ancestor.
• Structures that have the same function in
different organisms may come from quite
different origins. This phenomenon is
termed analogy.
Fins
Flippers
• Analogous structures do not
imply an evolutionary relationship,
but may indicate convergence. Examples:
• Eye structure in octopus and mammals.
• Wings in birds and butterflies.
• Fins in fish and flippers in mammals
Wings
Analogy in Eye Structure
• Eyes in cephalopods
Mammalian eye
Iris
(such as octopus) and
mammals have the same
function and are
structurally similar, but
have evolved from
different origins.
Octopus eye
Lens
Cornea
Retina
Retina
Iris
Lens
Cornea
Convergent evolution
hedgehogs, porcupines, &
echidnas — they all have
(independently-developed)
spikes! But hedgehogs
originate in Europe,
porcupines come from
North America, & echidnas
are from Australia.
ANALOGOUS STRUCTURES
Convergent evolution
When unrelated species become more and more
similar in appearance due to them adapting to the
same kind of environment.
Phylogeny
The evolutionary relationships among organisms; the patterns of
lineage branching produced by the evolutionary history of the
organisms being considered.
Phylogenetic trees (family trees)
The evolutionary relationships among organisms; the patterns of lineage
branching produced by the true evolutionary history of the organisms
being considered. Represents true evolutionary history.
Phylogeny and Taxonomy
• The evolutionary history of a group
of related species is called
phylogeny.
• Reconstructing phylogenies
involves identifying and
classifying species to show
their evolutionary relatedness:
a scientific discipline (or area
of study) called taxonomy.
Common Ancestors
http://evolution.berkeley.edu/evolibrary/print/printable_template.php?article_id=evo_05&context=0_0_0
The central idea of biological evolution
is that all life on Earth shares a
common ancestor, just as you and your
cousins share a common grandmother.
Through the process of descent
with modification, the common
ancestor of life on Earth gave rise
to the fantastic diversity that we see
documented in the fossil record and
around us today. Evolution means
that we're all distant cousins:
humans and oak trees,
hummingbirds and whales.
Understanding phylogenies
Understanding a phylogeny is a lot like reading a
family tree.
The root of the tree represents the ancestral lineage,
and the tips of the branches represent the
descendents of that ancestor. As you move from the
root to the tips, you are moving forward in time.
When a lineage splits (speciation),
it is represented as branching on a phylogeny.
When a speciation event occurs,
a single ancestral lineage gives rise to two or more
daughter lineages.
Phylogenies trace patterns of shared ancestry between
lineages.
Each lineage has a part of its history that is unique to
it alone and parts that are shared with other lineages.
Similarly, each lineage has ancestors that are unique to
that lineage and ancestors that are shared with
other lineages — common ancestors.
Define:
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Evolution
Phylogenetic tree
Descent with modification
Homologous structures
Analogous structures
Divergent evolution
Convergent evolution
Pentadactyl limb
Answer series: p 3.48 Question 1 and 2