Transcript Chapter 15 Evolution

• Founder of modern
evolutionary theory
• 1831 Darwin became
a naturalist on the
HMS Beagle
• Studied animal and
plant life on
mapping expedition
to South America
and South Pacific
• Darwin studied
anatomy of insects,
reptiles, birds and
flowering plants
Galapagos Tortoises
• The inhabitants...state that they
can distinguish the tortoise from
different islands; and that they
differ not only in size, but in
other characters. Captain Porter
has described those from
Charles and from the nearest island to
it, namely Hood Island, as having their
shells in front thick and turned up like a
Spanish saddle, whilst the tortoises
from James Island are rounder, blacker,
and have a better taste when cooked.--Charles Darwin 1845
• That there must be a struggle for
existence among all individuals
• Organisms must struggle for
– Food
– Space
– Prey
• From ancient times, most people believed
all living things were created by a divine
being at the same time and remained
unchanged.
• By the time Darwin set sail, numerous
discoveries, including a rich fossil record,
had turned up importance evidence that
caused some scientists to question these
ideas.
• Geologists James Hutton and Charles Lyell
– After examining Earth in great detail, recognized
that Earth is many millions of years old, and the
processes that changed Earth in the past are the
same processes that operate in the present.
– Ex: volcanoes, earthquakes, erosion, continental
drift, etc.
The Grand Canyon, with
its many layers of rock,
was formed over millions
of years by the Colorado
River (erosion).
• Jean-Baptiste Lamarck - French
naturalist
– Published hypothesis of Inheritance of
Acquired Characteristics same year
Darwin was born
– Proposed that by selective use or disuse
of organs, organisms acquired or lost
certain traits during their lifetime.
• Traits could then be passed on to offspring
• Over time would lead to change in species
• Thomas Malthus - English economist
– Reasoned that if the human population
continued to grow unchecked, eventually
there would not be enough space and food
for everyone
• Forces such as war, famine and disease work
against the growth
– Darwin realized this was even more true
for plants and animals because humans
produce far fewer offspring
• Upon returning to England, Darwin began
studying his specimens and filling
notebooks with ideas.
• Shared ideas with friends but reluctant to
publish -- understood his ideas challenged
scientific and religious beliefs of his day
• After more than 25 years -- published On
the Origin of Species in 1859
Charles Darwin Published:
“On the Origin of Species”
Only some of the population
survive long enough to
produce offspring
• Darwin’s
observations led to
the conclusion that
individuals have
different variations
of traits that can be
inherited
Darwin bred pigeons with desirable
variations and he was able to
produce offspring with the same
features
• Breeder selects the
particular traits
• Darwin wondered if there
was some force in nature
similar to artificial selection
•NATURAL
SELECTION
• Mechanism for change in populations that
occurs when organisms with favorable
variations for a particular environment
survive, reproduce and pass variations
on to the next generation
• Organisms with less favorable variations
are less likely to survive and pass on traits
to the next generation
Tendency toward
Overproduction
• For example: Fish
lay thousands of
eggs
• Most of these eggs
will not survive
Individuals Exhibit Variations
• Example:
Fishes may
differ slightly in
color, fin and
tail size and
speed
Individuals with favorable traits
survive and pass on those genes
• Ex: A fast fish with
camouflaged skin will
be more likely to
survive and
reproduce. Thus,
passing along the
more desirable traits
to future offspring.
Populations evolve, or change
over time
• Gradually, the offspring of the survivors
make up a larger portion of the population.
After many generations the population
may look entirely different.
• Changes in structure or
body parts that aide in
survival
• To copy the
appearance of
another
species
• Color adaptation
so organism
blends with its
surroundings
• May take millions of
years to develop or
they may be rapid
• Ex: Slow---Sightless
mole rat
• Fast: Antibiotic
resistance
The Fossil Record
• Fossils
show
change
over
time
• Geographical Distribution
– Organisms live in different areas of the world,
but have similar adaptations
– Different ancestors, but similar environmental
pressures acting against it
• Descent with modification
• Modified
structure
that is seen
among
different
groups of
descendants
• Similar in function,
but different in
structure
• Ex: Bird
Wing/Butterfly Wing
• Any body structure
that is reduced in
function in a living
organism but may
have been used in
an ancestor
• Fish, reptiles, birds and mammals look
similar during embryological development
• Speciation, or the
formation of new species,
can only occur when
either interbreeding or
the production of fertile
offspring is somehow
prevented:
Reproductive Isolation
– Geographic isolation
– Temporal isolation
– Behavioral Isolation
• Occurs when two populations are capable
of interbreeding but have differences in
courtship rituals or other reproductive
strategies that involve behavior.
• Ex. Eastern and Western Meadowlarks
– Habitat overlaps, but will not mate with each
other because they do not respond to each
others song!
• Two populations are separated by
geographic barriers such as rivers,
mountains, or bodies of water.
• Ex. Colorado River separating the Abert
squirrel and the Kaibab squirrel (about
10,000 years ago).
• Two or more species reproduce at
different times.
• Example: Orchids. Release pollen on
different days, so they cannot pollinate
each other.