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PART 1
B_5 Biological Evolution
“How has life changed over time?”
Standard B-5
Demonstrate an understanding of biological
evolution and the diversity of life.
B-5.1 Introduction (sec 10.1-2)
What is a theory?
What is biological evolution?
Explain the difference between microevolution
and macroevolution.
List 2 other people who had ideas about
evolution (what were their ideas)
View VIDEO #2: Who was Charles Darwin?
Summarize the Theory of Evolution
First of all a quick reminder of the term THEORY:
– Well supported and tested explanation, which unifies a broad range of
observations (evidence)
Biological Evolution
– Cumulative genetic changes that occur in a population over time
(GRADUAL change over TIME)
• Changes due to gene mutations or crossing over
• Explains the similarities and diversity of living things.
– Microevolution: small changes affecting a single population (usually
over a few generations); changes in allele frequencies
– MACROevolution: dramatic changes that occur over long periods of
time; includes speciation (formation of new species) and mass
extinction
Origins of Evolutionary Thought
Erausmus Darwin (1731): English Doctor
– Grandfather of Charles Darwin
– Proposed ideas of common ancestry
Carolus Linnaeus (1735): Swedish Botanist
– Devised a standard classification system for living things; based
on similarities and evolutionary relationships
– Kingdom, Phylum, Class, Order, Family, Genus, Species
• Scientific Names: Homo sapein (Genus species)
Georges Buffon (1749): French Naturalist
– Proposed that species shared ancestors instead of arising
separately
– Rejected that the Earth was only 6000yrs old
Origins of Evolutionary Thought
James Hutton (1785) – Proposes that Earth is
shaped by geological forces that happen over
extremely long periods of time (estimates Earth
to be millions of years old)
Thomas Malthus (1798) – Predicts that the
human population will grow faster than the space
and food needed to sustain it.
Charles Lyell (1833) – Explained that processes
occurring now have shaped Earth’s geological
features over long periods of time.
Origins of Evolutionary Thought
Jean-Baptiste LAMARCK (1809) read pg376
– Proposed that organisms over long periods of time due to the
environment (evolve towards perfection and complexity)
– Inheritance of Acquired Characteristics (thru use or disuse)
• Use and disuse of organs cause organism to change; organism change
because they need to change; Ex: Bird doesn’t fly loses wings
Alfred Russel WALLACE (1858)
– 1848 made an expedition to the Amazon River and then Malay
Islands (made similar observations as Darwin)
– Wallace shared his findings with Darwin and Darwin presented
Wallace’s essay to the Linnaean Society
Charles DARWIN (1859)
– Sets sail on HMS Beagle (1831-1836), the voyage provides evidence
that leads to the foundation of his theory of evolution
• (1859)On the Origin of Species by Means of Natural Selection
(evolution by natural selection)
Darwin’s Observations (do not copy)
Collected Fossil Evidence….
– Fossils he collected RESEMBLED
organisms that were currently living.
– Was there a relationship between
fossils and similar modern animals?
– Found fossils shells of marine
organisms high in Andes Mountains
Galapagos Islands west of South
America
– The Island had different climates
– Tortoises on 3 different islands were
different on each Island to suit their
climate
B-5.1-4 How Does Evolution Work?
(sec 10.3,11.1)
Explain evolution by natural selection.
Summarize the four factors of natural selection.
Factors that affect genetic variation.
Explain microevolution in terms of allele
frequency.
View VIDEO #4: How does Evolution really
work?
Darwin’s Proposed Theory:
Evolution by Natural Selection
Organisms best fit for the environment reproduce and pass on
their traits; aka… “survival of the fittest”
http://learn.genetics.utah.edu/content/variation/recipe/
1. Variation… individual organisms differ w/in species; alleles variations
cause phenotypic variations
2. Overproduction… Organisms produce more offspring than can
survive; competition for limited resources; Struggle for Existence.
3. Adaptation… inherited trait (allele) that INCREASES fitness (ability
to survive)
4. Descent with Modification… as the environment changes
individuals with beneficial traits survive reproduce – resulting in new
populations with different traits (phenotypes)
Factors that affect genetic variation
Sexual reproduction increase genetic variation in a population.
– SEXUAL: offspring have alleles from 2 parents
• Meiosis creates egg and sperm with new combination of traits due to crossing
over
– ASEXUAL: mostly genetically identical offspring
• Involves 1 parent producing identical daughter cells thru Mitosis (binary fission)
• Mutations can occur and are passed on to offspring (cells)
Sources of Genetic Variation:
http://learn.genetics.utah.edu/content/variation/sources/
– Mutations – random changes in DNA; if occurs in sex cells then can
be passed on to offspring; creates new allele
• If it increases survival it is called an ADAPTATION
– Recombination (gene shuffling) – occurs thru crossing-over
Explain microevolution in terms of
allele frequency
Vocabulary reminder:
– Species = group of organisms that can reproduce to create fertile offspring.
– Population = organisms of the same species living in the same area (thus are able
to mate & share gene pool)
– Gene pool = all alleles in population (genetic make-up of population)
– Allele frequency = % of dominant of alleles compared with recessive alleles
If a genetic change (mutation) occurs in one individual it then becomes
part of the gene pool & can spread thru the population
– Also changing the allele frequencies in the gene pool
– If mutation increases fitness, then the new allele increase in frequency
MICROEVOLUTION: If one trait (phenotype) increases an organisms
fitness, then organisms with that trait may reproduce more AND
– Cause Changes in the population allele frequency (gene pool)
– Changes in the gene pool over time = microevolution
EXAMPLE: Gene Pool
How would the gene pool be affected if these mice lived in an
environment where the brown fur mice were more camouflaged?
– Brown allele freq = 120 brown / 200 total = .6 (60%)
– Black allele freq = 80 black / 200 total = .4 (40%)
120
Brown
Allele
80
Black
Allele
B-5.4 Other Mechanisms of Evolution
(sec 11.3 & 11.4)
Review Natural Selection (primary cause)
http://learn.genetics.utah.edu/content/variation/sources/
Summarize and provide examples of other factors
that lead to evolution within a population.
Explain the Hardy-Weinberg Principle and genetic
equilibrium.
View Video #6 – Why does evolution matter now?
Factors that Lead to Evolution
GENE FLOW: Migration
– Movement of genes in (immigration) or out (emigration) of population
GENETIC DRIFT: Small Population caused by chance
– Causes a SMALL population with a loss of genetic diversity
– Bottleneck Effect – destructive event that leaves only a few survivors
– Founder Effect – small # of individuals colonize a new area
MUTATIONS: New Alleles
– Random change in DNA sequence = new alleles (variations)
SEXUAL SELECTION: Choosing a Mate
– Females only produce eggs at certain time, which makes them choosy when
selecting a mate
– Certain traits increase mating success and over time become more pronounced
– Competition between males or a display of traits
– http://www.youtube.com/watch?v=Cd82a3LOw98
(REVIEW) NATURAL SELECTION: Survival of the Fittest
– Individuals more fit in an environment survive and pass on traits (alleles)
– http://www.pbs.org/wgbh/evolution/library/01/1/quicktime/l_011_03_56.html
-bottleneck effect:
Sudden reductions in population size can also alter
the resulting gene pools. Any environmental
condition in which many individuals are killed and
only a small number survive, creates a bottleneck
effect.
In this case a few peccaries with the
genotype bb survive a catastrope. These individuals
become the founders (originators) of a new peccary
population.
As they reproduce, the new gene pool is very
different from that of the original population.
GENETIC
DRIFT
GENE FLOW
VIDEO:
http://www.zo.utexas.ed
u/faculty/sjasper/images
/evolutionarychange.swf
Hardy-Weinberg & Genetic Equilibrium
Hardy-Weinberg Principle Allele Frequencies will
remain the same ONLY if ALL of the following…
–
–
–
–
–
Random Mating (no sexual selection)
Very Large Population (no genetic drift)
No emigration or immigration (no gene flow)
No Mutations (no new alleles added)
No natural selection ( no phenotype has advantage)
Genetic Equilibrium (constant Allele frequencies) =
NO Evolution
Hardy-Weinberg Equation
Purpose: Use the equation to predict genotype frequencies.
– Values predicted by equation are those that would be present if
population was in genetic EQUILIBRIUM.
– Predicted values (frequencies) are compared to actual
frequencies… if the genetic data does not match the population is
NOT in equilibrium: it is EVOLVING
EQUATION: p2 + 2pq + q2 = 1
– p = frequency of dominant allele (T)
– q = frequency of recessive allele
• p2 = frequency of homozygous dominant organism (TT)
• 2pq = frequency of heterozygous organism (Tt)
• q2 = frequency of homozygous recessive organism (tt)