Download Evolution

Unit 8 Notes: Evolution
Name: ______________________________
Charles Darwin
•
In 1831, at the age of 21, he set sail on a five-year voyage on the HMS Beagle,
collecting specimens and mapping South America & the South Pacific.
•
The Galapagos Islands
•
Darwin studied & compared the anatomy of many species of reptiles, insects, birds, &
flowering plants, that are unique yet similar to species seen in other parts of the world,
on the Galapagos islands.
•
By the end of his trip, Darwin was convinced that evolution occurs.
Evolution: The theory that species change over time.
•
Using data he gathered from the natural world, Darwin began to form his well-known idea of
evolution by natural selection.
•
In 1859, Darwin published a controversial book; “On the Origin of Species by Natural Selection”.
• Controversy led to criticism of Darwin’s ideas.
Natural selection: A mechanism for change in populations that occurs when organisms
with favorable variations for a particular environment, survive,
reproduce, & pass these variations on to the next generation.
•
Organisms with less favorable variations are less likely to survive and pass on traits to
the next generation.
•
The idea of natural selection is often referred to as “SURVIVAL OF THE FITTEST”.
• NOT the strongest, but the organism best suited to the environment.
Adaptation: any trait that aids the chances of survival & reproduction of an organism.
•
Darwin’s theory of natural selection can be applied to explain the evolution of adaptations in
organisms.
Mimicry: provides protection for an organism by enabling it to mimic the appearance of
another species.
Camouflage: A defensive adaptation that involves changes to the color of organisms that
enables an organism to blend in with its surroundings.
•
Organisms that are well camouflaged are more likely to escape predators and survive
to reproduce.
Adaptations can develop rapidly
•
•
•
•
Caused by changes in an organism’s metabolic processes
50 years ago, the antibiotic penicillin was considered a wonder drug because it
could kill many types of disease-causing bacteria.
Today, scientists know that penicillin is not as effective as it used to be because
many species of bacteria have evolved physiological adaptations that make
them resistant to penicillin.
Rapid changes have also been seen in pest organisms.
Evidence for Evolution
•
•
•
•
Most of the evidence for evolution comes from indirect sources.
Fossils are an indirect source of evolutionary history of animals such as whales
• Provide a record of earlier life.
• fossil record is incomplete
it shows that 40 to 50 million years ago, horses were a species of small, dog-sized animals
Fossils show change over time
Unit 8 Notes: Evolution
Name: ______________________________
Anatomical evidence
Homologous Structures: Structures with common evolutionary origin
• May be similar in arrangement (structure), function, or both
Analogous structures: Any body part that is similar in function but different in structure
•
Do not have a common evolutionary history.
• Bird wings are made of a set of bones, whereas insect wings are mainly composed of a tough
substance called chitin.
Homologous structures
Analagous structures
Vestigial Structure: A structure in a present-day organism that no longer serves its original purpose,
but was probably useful to its ancestor
• May develop as species change in form and behavior.
• May serve no function, but continue to be inherited as part of the body plan for that species.
•
Human appendix useless yet in other mammals, including primates, it is necessary to aid in
digestion of high cellulose diet
•
Human external ear muscles still present but useless
•
Humans have tailbones and some babies occasionally have tails
•
Human wisdom teeth are vestigial compared to other primates
•
Some snakes have skeletal limbs.
•
Cave dwelling crayfish have eyestalks yet no eyes.
•
Sometimes vestigial organs may be adapted for new uses.
Penguin wings can't be used for flight yet adapted for swimming.
Embryological evidence
Embryo: the earliest stage of growth & development of a plant or animal.
•
Similarities among vertebrate embryos suggest evolution from a common ancestor.
•
In the earliest stage of development, a tail and gill slits can be seen in all species.
•
As development continues, the embryos become more and more distinct.
•
Comparative embryology
Biochemical evidence
•
•
The most recent evidence for evolution has come from comparisons of DNA & RNA within
taxonomic groups.
One study of comparisons of RNA sequences led to the construction of an evolutionary tree that
shows 3 major groups: the eubacteria, the archaebacteria, and eukaryotes.
Unit 8 Notes: Evolution
Name: ______________________________
Mechanisms of Evolution
(Populations evolve; individuals don’t)
•
•
•
If an individual organism possesses a phenotype that isn’t adapted to the environment, it may
result in the individual’s inability to successfully compete.
However, within the lifetime of one individual, new features cannot evolve in response to natural
selection.
•
In other words: NO you can’t grow wings!! --- Redbull doesn’t count, either.
Rather, natural selection operates only on populations over many generations.
The Evolution of Species
•
•
•
Natural processes such as:
• Mutation: A change in the DNA sequence
• Genetic Drift: (AKA allelic drift) Alteration of genes by chance processes.
Founder effect: Occurs in a newly colonized area where a few individuals settle. In this case, the
gene pool is limited because no new genes enter the gene pool.
• Amish communities where there is much intermarriage and certain genetic disorders are
common such as Ellis van-Crevald syndrome.
Started from 1 couple that settle in Lancaster, PA in the 1770’s.
Sexual selection: Where females choose their mate based on physical appearance of the male.
• Brightly colored males and dully colored females.
The above natural processes & natural selection can lead to changes in the allelic frequency in a
population’s gene pool and possibly cause speciation.
• Allelic frequency: How often (%) a certain allele appears in a population.
• Gene pool: The sum of all genes among a population
• Speciation: The evolution of a new species.
Unit 8 Notes: Evolution
Name: ______________________________
Speciation
Species: A group of organisms that look alike & have the ability to interbreed & produce fertile offspring
in nature.
•
Evolution of new species can occur only when either interbreeding or the production of fertile
offspring is somehow prevented.
Speciation
Geographic Isolation
Geographic Isolation
•
•
Occurs if a physical barrier separates a population into groups.
Over time, each small population would adapt to the local environment through the process of
natural selection.
•
Eventually, the gene pools of each group would become so different that one could be considered
a new species.
• Example - Tree frogs that have been forced to separate because of drought in rain forests.
Polyploidy: The presence of multiple (an extra) sets of chromosomes
• Is the result of mistakes that occur during meiosis.
•
It’s estimated that nearly ½ of the known flowering plant species originated in this way, as well as
crops such as wheat, cotton, apples, and bananas.
Speciation can occur quickly or slowly
Gradualism: The idea that species originate through a gradual change of adaptations.
• Slow and steady
• Supported by fossil record
Punctuated equilibrium: The idea that speciation occurs quickly in rapid bursts with long periods of
stability in between.
• Results from extreme environmental changes, such as warmer temperatures or the
introduction of a new competitive species
Unit 8 Notes: Evolution
Name: ______________________________
Stabilizing selection: Natural selection that favors average individuals in a population
• Both extremes are chosen against; the average is favored.
• Example – predators easily see the larger spiders and the small ones die because they find it
difficult to find food
Directional selection: Natural selection that favors one of the extreme variations of a trait.
• The average and 1 extreme are chosen against
Disruptive Selection: Natural selection that favors either extreme of a trait’s variations
• The average organism chosen against
Factors of Evolution
Divergent Evolution: Evolution in which species that once were similar to an ancestral species diverge
(branch off; deviate)
• Occurs when populations change as they adapt to different environmental conditions,
eventually resulting in new species
Adaptive Radiation: Divergent evolution in which ancestral species evolve in a variety of species
that fit diverse habitats.
Convergent evolution: Evolution in which unrelated organisms evolve similar traits (converge:
come together)
• Occurs when unrelated species occupy similar environments and face similar selection
pressures.
Divergent evolution
Convergent evolution