Download Darwin`s Theory of Evolution

Darwin’s Theory of Evolution
Life is extremely diverse, with an
estimated 20 million or more species
(mostly insects), divided into six different
kingdoms.
Darwin’s Epic Journey
●Geologists were just beginning to suggest that the
earth was changing over time.
●Biologists were suggesting that evolution would
explain how modern organisms evolved over long
periods of time through descent from a common
ancestor.
Observations aboard the Beagle
●As Darwin travelled aboard the Beagle he observed
three distinct patterns of biological diversity; species
vary globally, species vary locally and species vary
over time.
Species Vary Globally
o Darwin noticed that similar yet different animals
inhabited similar habitats around the world.
o Example: flightless, ground dwelling birds (Rheas)
lived in grasslands of South America. They looked
and acted like ostriches but ostriches could only be
found in Africa. Darwin also found Emus in
Australia’s grassland and they,too were similar to
ostriches.
Emu
Ostrich
Rheas
Species Vary Locally
• Darwin noticed different, yet related, animals
lived in different habitats within a local area.
Example: while travelling the Galapagos Islands
Darwin noticed that island slightly differed in their
ecological conditions. He found giant tortoises
varied slightly in their shells from island to island
Species Vary Over Time
Darwin collected fossils and he noticed that
some fossils of extinct animals were similar
to living species.
Example: A fossil of a giant armoured
animal was very similar to that of a present
day armadillo.
16.2 An Ancient, Changing Earth
Hutton recognized that certain geological
processes were responsible for certain geological
features.
Example: Hutton proposed that forces pushed the
earth surface upwards and this gave rise to mountains
Dacite columns that formed tens of thousands of years ago when a lava flow cooled rapidly
against a glacier. Photo by Jackie Beckett, © American Museum of Natural History.
Uniformitarianism
● Lyell’s principle of uniformitarianism stated
that geological processes we see today
must be the same forces that shaped earth
millions of years ago.
Example: ancient rivers carved channels
and canyons just as our present rivers do
today.
●Darwin realized that if earth could change
over time living things could change over
time.
Change over time
Lamarck’s Evolutionary Hypothesis
● Lamarck suggested that all living things urge to
become more perfect and complex.
● As a result organisms change and acquire
characteristics to make them more successful in
their environment. This was known as “acquired
characteristics”.
Example: the black – necked stilt’s long legs were a
result of the bird’s ability to stretch their legs. Over
time, future generations would have their legs get
longer.
● Lamarck also suggested that these “acquired traits
could be passed on to their offspring. This was
known as “inheritance of acquired characteristics”.
Black-necked Stilt
Population Growth
●Malthus suggested that human populations
tend to grow faster than food supply. He
reasoned that war, hunger and disease
would keep population in check.
●Darwin reasoned that the same notion could
be true for other living things.He wondered
why others of a same species survived and
others perished.
Artificial Selection
● Darwin took up breeding plants and pigeons to
test the idea of artificial selection. The animals
and plants provided the variations and humans
selected those variations they find useful.
● Darwin realized that variation in a population
provided the raw material for evolution.
Evolution by Natural Selection: Competition
●Darwin used Malthus’s reading to come up
with the notion of a struggle for existence. All
members of a population must compete for
necessities of life.
Variation and fitness
● Darwin thought that the variation in a population
played a role in who survived.
● Some variations are better suited for the
environment than others and this increased the
organism’s ability to live and reproduce.
● These organisms had better adaptations.
●Those organisms with the best adaptations were more
likely to reproduce, meaning they had better fitness.
The difference in reproduction rates refers to the
“survival of the fittest”.
●
Natural selection takes into account that there are variations
in a population, those best suited will survive and produce
more offspring. From generation to generation, populations
continue to change as they become better adapted, or as the
environment changes.
Common Descent
● Darwin suggested that over many generations,
adaptations could cause successful species to
evolve into news species. This explains the
diversity of life and that species change over
time.
● Descent with modification proposes that all living
species are descended from common
ancestors. A tree of life links all living things.
Complete
Finch
activity.
Ref. p
472 in
M&L
Evidence of Evolution: Biogeography
● Biogeography is the study of where organisms
live now and where they and their ancestors
lived in the past.
● Darwin saw two patterns related to
biogeography. One pattern had closely related
species differing slightly when the climate
changed. Populations on the island were slightly
different from the mainland species.
• The second pattern had very distantly related
species develop similarly in similar
environments.
• Similar habitats around the world had similar
plants and animals that were very distantly
related.
• Darwin suggested that environmental pressures
had caused very distantly related species to
develop similar adaptations.
Comparing Anatomy and Embryology
● Darwin suggested that animals with similar
structures evolved from a common ancestor.
● The structures shared by a related species that
have been inherited from a common ancestor are
called homologous structures.
● Similarities and differences among homologous
structures indicate how recently these species
shared a common ancestor.
●Vestigial structures are inherited from
ancestors but have lost much of their
function if not all their function.
●Dolphins have hipbones that of are no
use, yet they may have played a role in
their locomotion while on land.
●Embryological development of
vertebrates is very similar, showing
evidence that organisms have descended
from a common ancestor.
Genetics and Molecular Biology
●Our advancements in genetics indicate that
all living things share the same DNA and
RNA to carry information from one
generation to the next.
●Genetics provides some of the strongest
supporting evidence of evolution.
Homologous molecules show structural and
chemical similarities at the molecular level. An
example is cytochrome c, a protein which
functions in cellular respiration for all types of
cells
.