evolution chapter 15. natural selection & the evidence for evolution ch. 15, sec. 1
TRANSCRIPT
EVOLUTION
CHAPTER 15
Natural Selection & the Evidence for Evolution
Ch. 15, Sec. 1
Evolution
Gradual change in a species over time due to adaptations, There are exceptions Science is Tentative
Development of new organisms from preexisting types of organisms Living things come from other living things New species come from other species
Characteristic changes in a population involve changes to genes These changes then get passed along through
the genes Who do you get your genes from?
Supported by a lot of evidence and data Fossil, Anatomical, & DNA
Charles Darwin (1809-1882)
Started off studying medicine
1831 signed on for a 5 year journey of South America on the HMS Beagle
Enjoyed nature & making observations
Noticed similar looking organisms on different continents
Darwin’s Clues
Collected fossils Observed the adaptations of plants &
animals allowing them to survive in particular environments
Adaptation = a trait (which is coded for by DNA in a gene) that allows an organism to be successful in its environment Like tools that help them get the job done
How are these organisms adapted to their environment?
Galapagos Islands
One of Darwin’s stops on the Beagle Group of volcanic islands off the west coast
of South America
Home to several species of finches Each species is adapted to the type of food
eaten
Darwin’s Hypotheses
Darwin hypothesized that all the species descended from ancestral finches
The ancestral finches flew to the Galapagos Islands over from mainland South America
Population changed over time to adapt to the environment
Darwin’s Observations
1. Overproduction Most species produce large numbers of
offspring (ex: rabbits) But why isn’t the earth overrun by rabbits? The environment will set a limit on how big
the population gets by causing deaths or limiting births
2. Competition within a species.
Observations cont.
3. Variation Within populations organisms have different
traits because of variations in genes Variations can be inherited (who do you get
your genes from?) Populations have multiple alleles for any
given trait (dark fur/light fur, tall ears/short ears, etc.)
In summary…
Organism’s that have superior traits/tools are better adapted
Therefore they’re more likely to survive Therefore they’re more likely to reproduce
and pass on the genes for the superior traits/tools
What “chooses” the superior traits?
ArtificialSelection
Darwin worked with breeding different variations on pigeons
Artificial Selection = humans select good traits in organisms to breed Ex: prettier roses, bigger chickens, sweeter oranges YOU see it all the time
Darwin hypothesized:
Something like Artificial Selection must be acting on the organisms living in the wild
Natural Selection
Natural Selection = mechanism for change in populations; organisms with favorable variations survive, reproduce, & pass on the variation to the next generation (offspring)
Organisms with the best adaptations (helpful traits, good “tools”) are most likely to survive & reproduce
Through inheritance the adaptations will become more frequent in the population
Who gets to evolve?
It is the population that evolves, not the individual If you like swimming, can you choose to evolve
gills? An individual can be born with a mutation If the mutation is an advantage (good “tool”)
for living in a particular environment then that individual will be more likely to survive & pass on that mutation to its offspring
Structural Adaptations
Why are these structures adaptations?
Mimicry = structural adaptation allowing one species to resemble another species
Camouflage = adaptations allows species to blend in with surroundings
Rapidly Developing Physiological Adaptations
Evolution is not always a slow process
Evident in antibiotic resistance (bacteria evolve too)
Resistance of insects to pesticides
Increased toxicity of snake poison
Fossil Evidence
Fossils show that over time species have gradually changed their form
A transitional species will have characteristics of both the ancient and modern organism there has to be something in between Ex: Do children automatically become adults?
Ex: Modern whales evolved from an ancient, land mammal
Anatomy Evidence
Studying anatomy can uncover structural evidence of a common ancestor
Homologous Structure = similar in build, different function; anatomical structures in different species inherited from a common ancestor
Homologous Structures
An early ancestor of all 4 species had a forelimb with similar structure (common ancestor)
Analogous Structures
Have closely related functions, but are built differently; does not indicate a common ancestor
Vestigial Structures = serve no function but resemble structures with functional roles in other animals
Embryology
Embryology = the study of how organisms develop
Early stages of vertebrate embryos look very similar
As development continues embryos of different species start looking less alike
DNA Evidence
All living organisms have DNA in common DNA codes for proteins The more closely related two species
are…. The more similar their DNA…. The more similar the proteins made in
their bodies are
Mechanisms of Evolution
Ch. 15, Sec. 2
Population Genetics
Gene Pool = all the alleles for a particular trait in a population are “pooled” together ex: all the alleles for short fur and long fur, all the
alleles for brown fur and black fur Allelic Frequency = percentage of a specific
allele in the gene pool % of brown fur alleles & % of black fur alleles
Genetic Equilibrium = maintaining the same frequency of alleles over time
Changes in Genetic Equilibrium
Mutations can cause variations to be added to the gene pool of a population
Genetic Drift = chance events changing a population’s genetic equilibrium
Natural Selection Acts on Variations - red (before) blue (after)
Stabilizing selection = natural selection that favors average individuals in a population
Natural Selection Acts on Variations - red (before) blue (after)
Directional selection = natural selection favors one of the extreme variations of a trait
Natural Selection Acts on Variations - red (before) blue (after)
Disruptive selection = individuals with either extreme of a trait’s variation are selected for
Evolution of a Species
Changes to a gene pool can lead to the evolution of a new species
Speciation = members of similar populations can no longer interbreed
Biogeography – Field Video
Geological Isolation = physical barriers divide a population
Over time, the
divided populations may become two species that can no longer interbreed, even if reunited
Reproductive Isolation = occurs when formerly interbreeding organisms can no longer mate and produce fertile offspring; 2 types 1. Genetic Isolation = genes of two populations
are so different they cannot produce fertile offspring
2. Behavioral isolation (ex: one population mates in the spring, another population mates in the fall)
Change in Chromosome Numbers = mistakes in cell division lead polyploid individuals (abnormal sets of chromosomes)
Polyploids can be sterile, unable to reproduce
Polyploids can also reproduce and generate a new species through interbreeding
Speciation Rates
Gradualism = species originate through gradual change of adaptations
Punctuated Equilibrium = speciation occurs in quick, rapid bursts
Patterns of Evolution
Divergent Evolution = species that were once similar evolve to look differently Adaptive Radiation =
ancestral species evolving to fit into a lots of different habitats
Field Museum Video
Convergent Evolution = very distantly related organisms evolving similar traits
Hummingbird moths are night-flying insects whose behavior and appearance are similar to those of hummingbirds. Explain how these two organisms demonstrate convergent evolution and analogous structures. (1 paragraph, 5-8 sentences)