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Evolution
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http://clipmarks.com/clipmark/2335D5D9-1411-4C05-906B-B818B2B50B8C/
Darwin and the
voyage of the Beagle
 In 1831 Charles Darwin
set out on a 5year voyage
that was to change history!
 He observed:
1. plants and animals are
well suited to their
environments
2. Similar ecosystems had
different species…why?
The Galapagos
 Darwin visited a diverse
group of Islands off S.
America.
 He observed:
characteristics of plants
and animals varied
noticeably between islands
http://www.world-atlas.us/south-america-map.gif
“I have not as yet noticed by far the most remarkable
feature in the natural history of this
archipelago; it is, that the different islands
to a considerable extent are inhabited
by a different set of beings.”
Charles Darwin
http://www.thebestofecuador.com/galapagos.gif
The Galapagos Giant Tortoise
 Differences are related to the environments in which the
tortoises live, and types of food they eat.
 Domed tortoises - live in the moist high-lands and feed on
grasses and low-lying shrubs.
 Saddle-backed tortoises live in arid regions and feed on
plants that are mostly above their head.
The Origin of The Species
Selection
 In 1859, Charles Darwin
published his thoughts.
 He proposed a mechanism
for evolution
 He proposed evolution had
been happening for
millions of years…and
continues…
 This was
REVOLUTIONARY!!!!
by means of Natural
Artificial and Natural Selection
 Darwin observed British farmers selectively
breeding plants and animals for increased
yield.
 He called this “artificial Selection” – humans
select from the natural variation among a
population
 Darwin believed a similar process of
selection occurred in nature
Survival of the Fittest
 Darwin observed a struggle
for existence.
 Individuals compete for
limited resources
 The ability of an organism to
survive and reproduce =
fitness
http://www.expo-shop.com/product/PGMIB05.jpg
 Fitness is the result of
adaptation
 Adaptation: an inherited
characteristic that increases
an organisms chances of
survival
http://farm1.static.flickr.com/49/125046333_7123c38e73.jpg
Natural Selection
 Darwin described the survival of the fittest
as “Natural Selection”
 Over time, natural selection results in a
change in the inherited characteristics of a
population.
 Species become fitter over time
 Natural selection can act in one of 3 ways:
1. Directional Selection
 Individuals at one end of the curve have higher
fitness and the whole curve shifts
http://www.biologycorner.com/resources/directional_selection.gif
2. Stabilizing selection
 Selection against both extremes keeps curve
narrow and in the same place
 Ex: baby birthweight
http://www.biologycorner.com/resources/directional_selection.gif
3. Disruptive Selection
 When individuals at the upper and lower ends of
the curve have higher fitness than in the middle
 The curve may split into two
http://img.sparknotes.com/figures/A/a3aa6bb95c7d70781cc0089d17f9160f/disrupt.gif
 Descent with
modification implies a
common ancestor
The central ideas of evolution are:
Life has a history
It has changed over time
Different species share common
ancestors.
A Cladogram showing the
evolution of species from a
common ancestor
Geographic Distribution of
Living Things
 Darwin concluded different species found
on different islands descended, with
modification, from a common ancestor
– Divergent evolution
Convergent evolution
 Entirely different
species in similar
environments evolve to
look similar –
convergent evolution
Arctic Cod
Ex: Fish in the Arctic and
Antarctic both contain
glycoproteins which
prevent their blood
freezing
Antarctic Notothenioid fishes
Examples of Convergent Evolution
 The Australian Spiny
Echidna and the British
Hedgehog
Convergent Evolution
 Bird Wing, Bat wing
and butterfly wing
Homologous body structures
 Homologous structures
have different mature
forms but develop from
the same embryonic
tissues
 Amphibians are
believed to have
evolved from lobe
finned fishes
Similarities in Early Development
 The early embryos of
many animals with a
backbone are so similar it
is hard to tell them apart
 The same groups of
embryonic cells develop
in the same order and in
similar patterns
http://biology.unm.edu/ccouncil/Biology_124/Images/embryos.jpeg
Summary of Darwin’s Theory
 Individual organisms differ from one
another. Some of this variation is inherited
 Organisms in nature, produce more
offspring than survive, and of the survivors,
not all reproduce
 Members of each species must compete for
limited resources
 Because each organism is unique, each has
different advantages and disadvantages in
the struggle for existence
Summary continued…
 Individuals best suited to their environment
survive, reproduce and pass on those
characteristics
 Species change over time. Over long periods
natural selection causes species to change. New
species appear, others may die out.
 Species alive today, have descended, with
modification, from those alive in the past
 All organisms on Earth are united into a single tree
of life
Speciation – the formation of new
species
 A species is: a group of organisms that breed with
one another and produce fertile offspring
 For new species to evolve populations must be
reproductively isolated.
Reproductive Isolation can occur as
a result of…
 Behavioral Isolation –
differences in courtship
 Geographical Isolation
– change in course of
a river
 Temporal Isolation –
separation of breeding
season
Eastern and Western Meadowlarks
are different species
The pace of evolution
Gradualism – Darwin believed evolution was a
slow and gradual process of change over
millions of years
 Punctuated equilibrium – there is some evidence
of fast “spurts” of evolution as a result of:
1. A small population becoming isolated
2. Migration of a population to a new area and rapid
radiation to fill new niches
3. Following mass extinction
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