Download Evolution

Evolution Review
Who’s the man?
Charles Darwin
What did Darwin observe on his
Journey on the HMS Beagle?
• Many different species of plant and animal
life
• Fossils of extinct animals
How did Darwin explain the
differences in the Galapagos
finches?
He proposed that the 13 different
finches had come from a…
• Common ancestor
What is a population?
• A group of one species of organism in a
specific geographical area that can
interbreed.
Evolution is a..
• Well-accepted theory of how organisms
have changed over time by natural
selection.
• Darwin based his ideas on:
• 1. observations of nature
• 2. Malthus’s theory about exponential
population growth
• 3. his experience breeding animals
Tenets of Evolution
•
•
•
•
•
Populations have the potential to grow…
exponentially
They don’t because..
resources are limited
There are differences in individuals (genetic
variation)
• These differences can help some individuals
survive better than others
• Those that survive longer pass more of their
genes on to the next generation.
What is Natural Selection?
• The idea that individuals with traits that
make them well-suited to the
environment will survive and reproduce,
passing on their genes, at a higher rate
than less suited individuals.
• This will cause a change in frequency of
alleles in the population
Process of becoming better suited
to the environment is called..
• Adaptation
• What does natural selection act on?
• On populations over many generations.
What is needed for natural
selection to occur?
• Genetic variation (differences) in the
individuals must exist
• Otherwise all members of the population
would have the same advantage for
survival
What are 4 sources of
genetic variation?
• 1. Mutations- errors in base pairs caused by mutagens,
energy exposure, or errors in replication
• 2. Meiosis- two events occur:
• Random alignment
• Crossing over
 3. Immigration- new genes come into population
 4. Sexual Reproduction- combining the alleles of
mother and father
What 4 processes change allelic
frequency?
• 1. Natural Selection- environment
determines which traits will survive and be
passed on
• 2. Artificial Selection (breeding)- humans
decide which traits will be bred for
• 3. Gene Flow
• 4. Genetic Drift
Gene Flow
• Genes moving in and out of a population
• Give two examples:
• 1. immigration– new individuals move in
• 2. emigration- individuals move out
Genetic Drift
• This is a ___________change in allelic
frequency that is due to chance.. Not
environmental pressure.
• Answer= RANDOM
Gradualism vs
Punctuated Equilibrium
• Hypothesis that evolution occurs in short
bursts of rapid change, then periods of no
change is…
• Punctuated equilibrium
• Hypothesis that evolution occurs gradually
at a slow, constant rate is..
• Gradualism
What has to happen for a new
species to become established?
• First, Reproductive Isolation from the
original group
• Example: a flock of birds gets separated and blown
toward an island by a storm
• They are now isolated from their original group on
another island.
• Over time, in 2 different environments, they become
more and more different
When does speciation occur?
• When they can no longer interbreed with
the original group of birds
• A speciation event=
• A new species
When a group of organisms starts
a new colony, it is called..
• The Founder Effect
What is a genetic bottleneck?
• This happens when a natural disaster
(earthquake, volcano, etc) kills off a group
of the original population, and the allelic
frequencies change (genes are lost). Now
the group has different amounts of the
alleles for certain traits.
When 2 species become …
• More different, it’s called…
• Divergence (diverse=different)
• More alike, it’s called…
• Convergence (converge=coming together)
What are Vestigial structures?
• Those anatomical features that no longer
have a purpose
• Examples: in whales…
• They have small back limbs, inherited
from an ancestor that moved on land.
See next slide.
What are Homologous structures?
• Similar structures in different species that
suggest that they have a common
ancestor
• Example: the forearm of many vertebrates
(humans, bats, alligators, etc) have similar
bones. See next slide.
Contrast:
Scientific theory,
law, and hypothesis
• Theory= an explanation of how a natural
phenomenon occurs
• Law= describes a phenomenon
(mathematically)
• Hypothesis= a prediction based on
research and prior knowledge