1. Ch. 16: Evolution of Populations

2. Ch. 16: Outline 16-3: The Process of Speciation Isolating Mechanisms
Testing Natural Selection in Nature
Speciation in Darwin’s Finches
Studying Evolution Since Darwin

3. Variation and Gene Pools
Genes control heritable traits.
Changes in genes produce heritable variation on which natural selection can operate.

4. Variation and Gene Pools
Genetic variations is studied in populations.
Population: Group of species in a specific area
Gene pool:
All genes (including different alleles) that are in population.
Relative frequency:
The Number of times that an allele occurs in a gene pool, compared to the number of times other alleles for the same gene occur

5. Sources of Genetic Variation
Two main sources of genetic variation:
Mutation
Genetic Shuffling (from sexual reproduction)
Mutation: any change in a sequence of DNA
Caused by a mistake in replication or radiation and chemicals in the environment
Some mutations are harmless, but others affect an organism’s fitness
Fitness: The ability to survive and reproduce

6. Sources of Genetic variation
Gene shuffling:
MEIOSIS!
Review
Segregation
Independent Assortment
Crossing-over
Thus, Sexual reproduction is a major source of genetic variation

7. Isolating Mechanisms
Because the definition of a species is a group of organisms that interbreed to produce fertile offspring, the gene pools of two populations must become separated enough to become new species.
As new species evolve, populations become reproductively isolated from each other.
Reproductive isolation: when the members of two populations can no longer reproduce with each other.

8. Isolating Mechanisms Three ways for reproductive isolation to occur:
Behavioral Isolation
Geographic Isolation
Temporal Isolation

9. Isolating Mechanisms
Behavioral isolation: Two populations have differences in courtship rituals or other reproductive strategies that involve behavior.
Geographic isolation: Two populations are separated by geographic barriers such as rivers and mountains.
Temporal isolation: Reproduction occurs at different times of the year.

10. Reproductive Isolation Formation of new species
Concept Map
Reproductive Isolation
results from
Isolating mechanisms
which include
Behavioral isolation
Temporal isolation
Geographic isolation
produced by
produced by
produced by
Behavioral differences
Different mating times
Physical separation
which result in
Independently evolving populations
which result in
Formation of new species

11. Testing Natural Selection in Nature
Darwin’s finches in the Galapagos Islands are the perfect example on natural selection happening in nature.
Natural selection shaped the birds beaks on each island depending on the food source
Figure

12. Chapter 17 The History of Life 17-1: The Fossil Record
Fossil and Ancient Life
How Fossils Form
Interpreting fossil evidence
Geologic Time Scale
17-4: Patterns of Evolution
Extinction
Adaptive Radiation
Convergent Evolution
Coevultion
Gradualisms vs. Puntuated Equilibrium

13. Fossils and Ancient Life
Scientist who study fossils are called paleontologists
Fossil Record: the information about past life, which includes structure of organisms, what they are, and their environment

14. Fossils and Ancient Life
The fossil record provides evidence about the history of the Earth.
The fossil record indicates that species have change over time (evolution). Certain fossils can only be found in older rocks, for example (and are not found in any recent rocks).
Extinct: a species that has died out.

15. How fossils form
Most fossils form in sedimentary rock (formed when existing rock is broken down into sand, silt, etc.) Layers of earth build up over time on top of the fossil and some stay preserved.
Forces inside the earth lift rocks up into mountain ranges and wind and rain erode the rock. Then old fossils are exposed

16. Extinctions
Reasons for extinction: competition for resources, changes in the environment
Mass Extinctions: wipe out entire ecosystems
Possible causes  asteroids, volcanoes, changes in sea level.

17. Adaptive Radiation
Adaptive Radiation: the process of one species evolving into diverse forms that live in different ways.
Darwin’s finches had one common ancestor

18. Convergent Evolution
Sometimes unrelated organisms evolve to appear similar. The process of this is called convergent evolution.
It happens when organisms are in the same type of environment.
Ex: Many water animals have fins to help them swim even if they are totally unrelated (shark and dolphin)
Analogous structures: structures that are similar in structure and function (but in unrelated species)

19. Coevolution
An evolutionary change in one organism can sometimes result in a corresponding change in another organism
Coevolution: the process by which two species evolve in response to changes in the other over time
Ex. Flowers and pollinators

20. Gradualisms vs. Punctuated Equilibrium
Modern scientists disagree with Darwin about the speed of evolution.
Darwin believed that the speed of evolution is a slow, gradual process (gradualism).
The fossil record indicates that this is true for some species. But other species are produced by short periods of rapid change (also supported in the fossil record).

21. Gradualisms vs. Punctuated Equilibrium
Puntuated equilibrium: the pattern of long, stable periods interrupted by brief periods of more rapid change
What causes punctuated equilibrium?
Migration
Isolation
Mass Extinctions

22. Developmental Genes and Body Plans
Puntuated equilibrium: the pattern of long, stable periods interrupted by brief periods of more rapid change
What causes punctuated equilibrium?
Migration
Isolation
Mass Extinctions