APBEvo1 Evolution Intro modification.ppt

Change over time, descent with modification, population evolve

1. Evolution Intro
change over time. descent with
modification. populations evolve,
not individuals.

2. Charles Darwin
•(1809-1882) Englishman. Medical school dropout.
Obsessed with nature. Aspiring clergyman. Married
his cousin.
•The 5 year trip that changed Darwin’s life: The
Voyage of the HMS Beagle
▫collected plants and animals. Noticed they were
suited to diverse environments.
▫Also found species resembled others around the
world
▫Influenced by geology (Lyell)
Earth shaped by slow-acting forces that are still in
work today
▫The Galapagos. (finches)

3. •Alfred Russell Wallace. British naturalist that
developed a theory very similar to Darwin’s. (His
ideas were submitted for publication first)
•Darwin publishes On the Origin of Species in 1859. His
ideas convinced scientists of evolution to explain
species diversity.
▫Through time species accumulate differences; as a
result, descendants differ from their ancestors. In this
way new species arise from existing ones.
▫Natural Selectionis the mechanism for evolution
▫Descent with modification: species share a common
ancestor and diverged gradually over time

4. Darwin’s Ideas
•Descent with Modification.
▫organisms share similar characteristics suggesting common
ancestry.
▫accumulate adaptations as environment changes, leading to
different species
▫‘gaps’ in record filled with fossil evidence
•Natural Selection.
▫Variation in a population
certain traits will give a higher probability of surviving to
reproduce
▫Species produce more offspring than survive.
lead to accumulation of favorable traits in the population over
generations
causes organisms to become suited specifically to their
environment
▫May result in new species forming

5. Evidence
•Fossils
▫evolutionary changes over time; “missing links”
▫compare current (extant) organisms with extinct ones
▫Use geologic information and carbon dating to estimate age of fossils
•Homology (homologous structures)
▫similar characteristics (but function differently) resulting from
common ancestry
forelimb of mammals
vertebrate embryos
▫vestigalstructures: “leftover” structures from an earlier ancestor
(was important once upon a time)
pelvic bones in a whale, snake, appendix

6. Evidence
•Biogeography
▫geographic distribution of species
▫influenced by continental drift (plate tectonics)
▫Convergent evolution (similar environments yield
similar anatomies)
More evidence supporting organisms adapt to be best
suited to their environment!
•Molecular Evidence
▫DNA sequences similar from shared genes
▫relationships between groups of organisms

7. •microevolution: change in allele frequencies in a
population over generations (small scale)
▫Result from accumulation of mutations
•Variation: differences among individuals in a
population
▫only genetically determined phenotypes
(characteristics) will be subject to natural
selection
▫without variation there is no evolution

8. The White-Striped Clover…
•Discuss with your group members your answers to this
case study. Think specifically about the answers to the
following….
▫How does this case study illustrate the process of natural
selection? What is the evidence that it occurred?—Be able
to justify your answers.
▫What is “selection pressure”? How is it illustrated in each
habitat? How does this affect the survival and reproduction
of the clover?
▫Thinking more broadly…what influences natural selection
in all organisms?

9. •Selective pressures
▫A phenotype (physical traits/behaviors) is selected for
or against depending on the environment in which an
organism lives
▫Survival benefit or disadvantage
▫Lead to differential survival and reproduction, driving
natural selection
Examples: climate, food, predators, diseases, humans

10. Influences on Variation
•Geography (geographic variation)
▫differences in the genetic composition of populations of the
same species
▫Affected by environmental differences
•Mutations
▫change in the nucleotide sequence of DNA
▫only those present in gametes will be passed to offspring
▫usually deleterious (harmful)…very few are beneficial
•Chance/random events
▫chromosomal shifts
▫recombination during meiosis

11. Influences on Natural Selection
•Competition = Differential Survival
▫Individuals with more favorable phenotypes will survive and
reproduce…passing on their traits to subsequent generations
•Genetic Variation and Mutation
▫Diverse genes allow for survival in changing environments
▫Variation results from mutation
•Environment
▫Fluctuations in environment cause specific traits to be favored at
certain times
▫Human impacts
•Chance and Random Events
▫ie. Earthquake splits population in two

12. •Adaptation: inherited characteristics of organisms that enhance
their survival and reproduction in specific environments
•Natural Selection: a process in which individuals that have certain
inherited traits tend to survive and reproduce at higher rates than
others because of those traits.
▫acts on populations, not individuals
▫only selects for heritabletraits that exist within a population
▫is specific to the environment in a particular time (flexible)
▫consistently improves the match between organisms and their
environment
•Fitness: the number of surviving offspring in the next generation
(measure of reproductive success)
•Artificial Selection: human modified traits in a population due to
selective breeding (agriculture, domestic animals)
•Convergent Evolution: independent evolution of similar features in
different lineages (analogous structures)