Download Theories of Evolution

Evolution
• Fossils indicated that living
things have changed.
• Several scientists had ideas
to explain how.
1) Lamarck
- French scientist
- Late 1700’s- early 1800’s
- “acquired traits” theory:
traits are not determined by genes but
by “need”
EX: giraffe necks grow longer because they
stretch to reach the leaves higher up.
2) Charles Darwin
• English scientist
• Developed his theory of “natural selection”
in the mid 1800’s
• Was a naturalist on the HMS Beagle
(traveled around the world, mostly the
southern hemisphere) for 5 years.
Voyage of the HMS Beagle
Darwin’s observations
Noticed organisms had some similarities
even when they lived far apart.
* Darwin’s Finches
Kept records & collected specimens
Published “The Origin of Species…”
Darwin’s Finches
• Good example of how evolution occurs
• Each Galapagos Island has its own unique
species of finch
• Each finch had a head and body well-adapted for
life on that island
• The finches were different species, but looked
similar
•Darwin realized that the finches
had a common ancestor
•He proposed that originally a few
seed-eating finches had flown to
the islands from mainland. Over
millions of years, the finches
adapted to the foods available on
each island – and evolved into
separate species.
Darwin’s ideas that served as a
basis for theory of natural selection
1. All organisms produce more offspring
than can survive.
2. Population numbers remain fairly
constant over long periods of time.
3. Organisms in a species show wide
variation.
4. Some variations are inherited and
passed on to the next generation.
Units of Variation
• Genes carry inheritable characteristics,
also source of random variation
– crossing over
• Mutations cause variation
– missing letters in DNA
Then Darwin made 2 deductions:
1. Since most offspring don’t survive, all
organisms must have to struggle for
survival. (Others are eaten, or die of
disease.)
2. The ones who survive and reproduce
will pass on their genes.
Mutations play big role in
natural selection
Rabbit Tale Maybe once upon a
time all rabbits had short
ears and managed OK.
Then one day a mutant with big ears
was born.
She was always the first to dive for cover.
Pretty soon, she had babies; some inherited
her big ears.
They all dived for cover as fast as their mom
– faster than the short earred rabbits.
Eventually, only the big earred rabbits are
left.
Natural Selection
Nature selects those that are best adapted
to survive.
“Survival of the Fittest”
Any adaptive advantage (a favorable trait)
that an organism has
is passed to offspring.
Example of evolution through
natural selection
Cockroaches
Over the centuries, as man and
cockroaches have shared homes,
cockroaches have become smaller and
flatter – easier access to hiding places.
(Large, fat ones more easily stomped.)
Another example - antibiotic
resistance by natural selection
• Someone gets sick
• Give them antibiotics
• 99% of the bacteria are killed; only the
antibiotic resistant mutants survive
• They thrive and flourish
• Person gets sick again
• Bacteria cannot be killed by antibiotics
Artificial Selection
• Breeding for certain
traits
• Environment is very
easy – all organisms
survive
• Breeder for (selects)
the trait he or she
Wants in offspring
Ex – color, size
Evidence of Evolution
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Fossils
Similarity of embryos
Homologous and analogous structure
Vestigial structures
Similarities in macromolecules
Fossils – tell us that organisms that
once lived on Earth are not here
any more.
Embryoes of all vertebrates
are similar – common ancestor
Homologous Structures – similar
structures with similar functions.
Suggest a common ancestor.
Analogous Structures
Structures in unrelated organisms that carry
out same functions:
EXs - Kidneys in mammals and Malpighian
tubules in insects
Lungs in mammals and gills in fish
Wings of insects and wings of birds
Vestigial Structures
• Examples: appendix, wisdom teeth, human tail
bone
• Interpretation: the vestigial structure was
functional in some ancestor of the modern
organism
• Snakes have pelvic bones; they are known to be
the descendants of four-legged reptiles.
• Vestigial features.The skeleton of a baleen
whale, a representative of the group of
mammals that contains the largest living
species, contains pelvic bones. These bones
resemble those of other mammals, but are only
weakly developed in the whale and have no
apparent function.
Appendix in human
Beneficial mutations give: rise to new genetic traits
(adaptive traits) that give an organism an
advantage in a changing environment and
produce more offspring with those traits - natural
selection. Through time these adaptive traits
become more prevalent in a population.
Evolution is the change in genetic makeup of a
population through successive generations. New
species can be formed, or is life forms cannot
adapt they will decline or become extinct.
Biodiversity is a result of the ongoing
processes of evolution and extinction.
Biodiversity sustains life and provides genetic
raw material for adaptation to future changes in
environmental conditions
Adaptive Radiation
• Adaptive radiation – many related species
evolve from a single ancestral species
Examples: Galapagos tortoises, finches –
diverged in response to food source
• Beak differences in Hawaiian
honeycreepers
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Near losses…
The cheetah, Acinonyx jubatus, is the sole member of its
genus. Twenty thousand years ago, cheetahs roamed
throughout the savannahs and plains of four continents:
Africa, Asia, Europe, and North America.
About 10,000 years ago - because of climate changes - all
but one species of the cheetah, jubatus, became extinct.
With the drastic reduction in their numbers, close
relatives were forced to breed, and the cheetah
became genetically inbred, meaning all cheetahs are
closely related.
http://www.nyarugame.co.za/cheetahdivert.html
Loyola University, New Orleans
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A genetic mutation in a fiveyear-old child from Berlin is
responsible for his bulging well
defined muscles. Dr. Schuelke,
the boy's doctor since his birth
says the youngster doesn't
stand out on the playground,
however, he can perform 'feats
of strength' when he puts his
mind to it. Dr. Schuelke tested
the baby for mutations in the
myostatin gene and found both
copies of the gene were
mutated. His body wasn't
producing myostatin, which
regulates muscle growth and
muscle mass in humans.