Download THE THEORY OF EVOLUTION

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.
• 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.
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.
• 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.
• 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
• 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.
• 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.
• 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.
Fish embryo
Pig embryo
Chicken embryo
Human embryo
• 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.
• 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.
• Rather, natural selection operates only on populations over many
generations.
• 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 vanCrevald 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.
• 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.
• 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 (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.
Chrysanthemum: an
example of speciation
due to polyploidism.
• 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
• 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
• 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.