This document discusses key concepts related to Darwin's theory of evolution by natural selection. It begins by describing Darwin's theory as a detailed, testable explanation for evolution that combines Mendel's ideas about heredity with observations of variation in nature. The document then presents examples of different types of natural selection, including scenarios where selection favors extreme or average traits. It also addresses other mechanisms of evolution such as genetic drift, gene flow, mutations, and speciation.

2.  Called “one long
argument” for
evolution
 Hundreds of
thousands of
observations
 Detailed, testable
theory

3.  No mechanism for HOW
variation is passed from
parent to offspring
 Modern synthesis:
combination of Mendel’s
and Darwin’s ideas

4.  Comparing fossils
presents a pattern of
gradual change
 Darwin found gaps in
the fossil record

7.  Scenario 1: Leaves
towards the bottom of trees
are disappearing. Some
giraffes can reach leaves
higher up, while others’
necks are not long
enough?
 Which giraffes will thrive?
Which giraffes will die out?
 What will future
generations look like?

8.  Scenario 2: A certain species of rabbits in a dense forest
come in brown and white fur colors. Hawks, soaring
overhead, often eat the rabbits.
 Which rabbits will be easier to spot?
 Which color trait will more likely be passed on to future
generations?

9.  Individuals that display an “extreme” trait are
selected for. Other individuals are selected
against.
 Population shifts toward this trait, away from the
opposite.

10.  Scenario 3: Lizards
range in size from tiny
to very large. Small
lizards generally run
very slowly while
large lizards are
usually the easiest for
predators to see.
 What size lizard
stands the best
chance of survival?

11.  Scenario 4: Human
babies of very low
birth weight are often
more prone to
disease. Babies of
very large weights are
difficult for mothers to
safely deliver.
 What size babies
stand the best chance
of survival?

12.  Individuals that display an average trait are selected for.
Individuals that display extreme traits are selected
against.
 Population shifts towards the average trait, and those
with extreme forms die off.

13.  Scenario 5: Limpets are marine animals that attach to
rocks. Their color varies from pure white to dark brown.
White-shelled that are on rocks covered with goose
barnacles (also white) are at an advantage. On bare,
dark-colored rocks, brown limpets are at an advantage.
 What “advantage” is being referred to above?
 If you were a dark limpet,
where would you live?
A white limpet?
 What color would have the
hardest time surviving?

14.  Individuals that display either extreme are
selected for. “Average” individuals are selected
against.
 Population shifts towards away from the average
trait, towards BOTH extremes.

15.  Design three example situations (1 paragraph
each) representing the three types of selection
we covered. Include the following:
1. Description of the animals involved and their traits
2. How is nature selecting for/against certain animals
3. Which trait will be come more common/less common
and why?
4. Name the type of selection.

16. 1) A group of crabs live on
a sandy beach. The
crabs range in color from
very light tan to dark
brown.
2) Seagulls, flying
overhead, eat the crabs.
They can more easily
see the dark crabs, since
the lighter ones blend in
with the color of the
sand.
3) Because the seagulls
more easily eat the dark
crabs, the lighter ones will
more likely survive and
reproduce, passing that
trait onto their offspring.
4) This is called “directional
selection.

18.  Change in the allele frequency of a population
over time

19.  Does chance
play a role?
 Is evolution
predictable?

20.  Populations will
remain at equilibrium
(and therefore not
evolve) unless some
outside factor affects
them
 Equilibrium: frequency
of alleles is
unchanging

21. 1. Natural Selection
2. Sexual Selection
(mate choice)
3. Mutations
4. Gene flow (migration)
5. Genetic Drift and
population bottlenecks

22.  Movement of
individuals
(and alleles)
from one
population to
another
 What are
some
barriers?

23.  Change in allele frequency
caused by chance events
 More common in small
populations
 Can be beneficial, harmful, or
neutral
 Examples:
• Founder Effect
• Population Bottleneck

25.  Environmental factors allow the development of
similar traits in very different organisms
 Ex: bats, beetles, birds

26.  Descendants of a
single ancestor
diversify into species
that fit into different
parts of the
environment.
 Adaptive Radiation-
when a new
population is in a new
environment it will
undergo divergent
evolution until the
environment is full.

27.  Species that live near
one another evolve to
benefit one another
 Ex. Yucca moth and
Yucca plant

28.  Adaptive Radiation –
one species,
subjected to different
environmental
pressures, can evolve
into multiple species

29.  …formation of a new
species
 Often, one species can
branch from another
 Extinction: the death of all
members of a single
species

30.  Gradualism – tiny changes
become large-scale changes
over a long period of time
 Punctuated Equilibrium –
sudden environmental
changes lead to new species
developing “quickly”

32. Morphological Concept: uses similarities
(physical and physiological) between
organisms
Biological Concept: group of organisms
that can breed and have fertile offspring

33. Geographic Isolation (Allopatric speciation)
Reproductive Isolation (Sympatric
speciation)