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Chapter 4-1
Evolution
One aspect of biodiversity is genetic diversity.
Goals for today:
 Be able to explain the importance of genetic diversity in the process of natural selection.
225 million years ago
Plate tectonics: movement of large plates characterized the Mesozoic era.
Continental Drift: Alfred Wegener
How did the movement of continents lead to the evolution of new species?
GEOLOGIC PROCESSES AND EVOLUTION
 The locations of continents and oceanic basins influence climate (temp. + precipitation over long
periods of time)
 The movement of continents have allowed species to move.
 Separation has led to geographic isolation leads to new species evolving
 How has the extinction of some species led to the evolution of others?
 Biologist estimate that over ___% of the species that have ever lived are now extinct!
Natural Selection
Asteroids and meteorites have wiped out large numbers of species and created opportunities for new species.
Natural selection: change in a population’s genetic makeup over generations
 one mechanism of evolution
Mutations can add variety to DNA.
What causes mutations in DNA?
EVOLUTION, NATURAL SELECTION, AND ADAPTATION
 Mutations: random changes in the structure or number of DNA molecules in a cell that can be inherited
by offspring.
 Can be caused by: chemicals, meiosis, UV, radioactivity, X-rays.
 Some mutations can cause cells to divide out of control. This is known as _____.
 Radiation that is strong enough to damage DNA is known as (ionizing, non-ionizing) radiation.
Mutations
Mutations are:
 Always occurring
 Provide genetic diversity
 Not always harmful
Ex. Sickle cell anemia, ΔCCR5, any mutation that conveys antibiotic resistance
 3 conditions are necessary for biological evolution:
 Genetic variability
 heritable
 differential reproduction- having more offspring than others
Fitness
Fitness: a measure of the differential reproduction.
High fitness: well adapted to its environment and reproduces more successfully.
Low fitness: not well adapted to its environment and doesn’t reproduce very successfully.
In the dry grassy environment, the rabbits on the right will have higher fitness.
Why is genetic variation important for natural selection to occur?
T/F. Mutations are always harmful.
Natural Selection causes the best adapted individual to have higher fitness
Limits on Adaptation through
Natural Selection
A population’s ability to adapt to new environmental conditions through natural selection is limited by its gene
pool and how fast it can reproduce.
 Humans have a relatively slow generation time (decades) and output (# of young) versus some other
species.
A cancer is wiping them out.
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How is the cancer spreading?
What can conservationists do to prevent their extinction?
Should they be trying to prevent their extinction?
Good at cleaning up road kill, eating ferel cats, and foxes ( which is an ecological _______)
The Tasmanian devil is in a extinction vortex:
 As a population size gets smaller and smaller, the likelihood of it surviving decreases faster than the
population size decreases
 So the population is drawn strongly towards extinction
 Caused by small population size
 Low genetic diversity
 Increased inbreeding, leading to recessive diseases appearing
 This is what type of feedback?
 The devils eat ferel cats and foxes that were introduced to the island.
 These organisms depend on the survival of the devils.
 Population bottlenecks occur when a population’s size is reduced for at least one generation.
 If all individuals in the population are similar in DNA, they are at greater risk for extinction because there is no
variation.
 Limits species ability to evolve any further.
 Founder Effect
 Founder effect: when a new colony is started by a few members of the original population.
 This small population size means that the colony may have:
 reduced genetic variation from the original population.
 Common Myths about Evolution through Natural Selection
True or False:
 The fastest and strongest are most fit.
 Organisms develop certain traits because they need them.
 Organisms can pick the traits that they want and acquire them during their life time.
 You can reach genetic perfection.
 Check for Understanding:
 1. What are the 3 conditions needed for biological evolution?
 2. Why is genetic diversity important to the survival of species?
 3. What is a bottleneck and how does it lead to the founder effect?