Early scientists proposed ideas about
evolution.
Evolution- is the change of a species over
time where a descendant become different
from their ancestors
Species- is a group of organisms that can
reproduce and have fertile offspring.
There were many important naturalists in the
18th century.
– Linnaeus: classification system from kingdom to
species
– Buffon: species shared ancestors rather than arising
separately
– Erasmus Darwin: more-complex forms developed
from less-complex forms
– Lamarck: environmental change leads to use or
disuse of a structure
E. Darwin
Lamarck
Theories of geologic change set
the stage for Darwin’s theory.
• There were three theories of geologic
change.
• Catastrophism- natural disasters such as floods
and volcanic eruptions cause evolutionary
changes in species or extinction
• Gradualism- slow change over a long period of
time (gradual- slow)
• Uniformitarianism- states that geologic
processes that shape the Earth are uniform
through time (uniform- always stays the same)
• Charles Darwin – p. 290
WHO? British naturalist
WHAT? 5 year voyage on the Beagle
from England around the world
WHERE? South America
(Galapagos Islands)
WHY? Study variation in life forms
Darwin Video
• http://my.hrw.com/content/hmof/science/hi
gh_school_sci/tx/gr912/hmd_bio_9780544073890_/dlo/biology
videoclips
Darwin observed differences
among island species.
• Variation is a difference in a physical trait.
– Galápagos tortoises that live in areas with tall
plants have long necks and legs.
– Galápagos finches that live in areas with
hard-shelled nuts have strong beaks.
• An adaptation is a feature that allow an
organism to better survive in its
environment.
– Species are able to adapt to their
environment.
Darwin observed fossil and geologic
evidence supporting an ancient Earth.
• Darwin found fossils of extinct animals that
resemble modern animals.
• Darwin found fossil shells high up in the
Andes mountains
After his voyage, Darwin spent over 20
years conducting research on evolution
• Darwin noticed a lot of variation in
domesticated plants and animals.
• Artificial selection is the process by which
humans select traits through breeding.
ex) faster horses, better fruiting plants
neck feathers
crop
tail feathers
Theory of Natural Selection
• Natural selection is a mechanism by which
individuals that have inherited beneficial
adaptations produce more offspring on average
than do other individuals. “survival of the fittest”
• Heritability is the ability of a trait to be passed
down.
• There is a struggle for survival due to
overpopulation and limited resources.
• Darwin proposed that adaptations arose over
many generations.
Four main principals….
• 1. Variation- heritable differences
• 2. Overproduction- having lots of offspring
increases chance that some will
survive ex) fish and reptile eggs
• 3. Adaptations- allow individuals to survive better
than other individuals , more successful
individual live longer and reproduce
• 4. Decent with modifications- more individuals
will have more favorable traits in future
generations
Interactive Natural Selection
• http://my.hrw.com/content/hmof/science/hi
gh_school_sci/tx/gr912/hmd_bio_9780544073890_/dlo/animat
edbiology
Evidence of Evolution
1. Fossil Records- Paleontology- the study
of fossils or extinct organisms
2. Geography
3. Developmental Similarities
»
»
»
Notochord
Dorsal nerve cord
Pharyngeal arches
• 4. Anatomy
• Homologous structures- similar in structure but
different functions
Human hand
Mole foot
Bat wing
• Analogous structures- similar function but are not
similar in origin
» Ex) bat wing and insect wing
Structural patterns are clues to
the history of a species.
• Vestigial structures are remnants of
organs or structures that had a function
in an early ancestor.
Molecular and genetic evidence
support fossil and anatomical evidence.
• Two closely-related organisms will have
similar DNA sequences
Embryonic Evidence
Fossil Evidence
http://my.hrw.com/content/hm
of/science/high_school_sci/tx/
gr912/hmd_bio_9780544073890
_/dlo/thatsamazing/ind
Genetic variation in a population increases
the chance that some individuals will
survive.
• Genetic variation is stored in a
population’s gene pool.
– made up of all alleles in a population
– allele combinations form when organisms
have offspring
Sexual selection occurs when certain traits
increase mating success.
• Sexual selection occurs due to higher cost
of reproduction for females.
– males produce many sperm continuously
– females are more limited in potential offspring
each cycle
• There are two types of sexual selection.
– intrasexual selection: competition among
males
– intersexual selection: males display certain
traits to females
Geographic barriers can cause isolation.
– called geographic isolation
– physical barriers divide population
• Temporal barriers can cause isolation.
– called temporal isolation
– timing of reproductive periods
prevents mating
Evolution from natural selection
isn’t random
• Convergent evolution
describes evolution
toward similar traits in
unrelated species.
Divergent evolution describes
evolution toward different traits in
closely related species
How do convergent and divergent
evolution illustrate the directional
nature of natural selection?
Species can become extinct
Extinction is the elimination of a species from Earth.
– occurs at roughly the same rate as
speciation
– usually affects a few species in a
small area
– caused by local changes in
environment