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JJA Obico, Instructor, Department of Biology
Natural Theology
Philosophy dedicated to
discovering the Creator’s plan by
studying nature
Classify species in order to revealy p
the steps of life that God had
created
Carolus Linnaeus
- sought to discover order in the
diversity of life
- founder of Taxonomy
Jean Baptiste Lamarck
In-charge of invertebrate
collection at the Natural History
Museum in Paris
Compared current species toCompared current species to
fossil forms
Use and Disuse
Inheritance of Acquired
Characteristics

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Biological Evolution
Descent with modification
Charles Darwin and Alfred Wallace
Descent
- Transfer of genetic material to offspring overtime
a. Clonal reproduction (asexual)
b. Sexual reproduction
Biological Evolution
Modification
- Change in genetic material
- Mutation; genetic
recombinationrecombination
What evolves?
Population
- A group of individuals of the same species
usually geographically delimited and
typically have a significant amount of gene
exchangeexchange
Species
- Consists of group generally intergrading,
interbreeding populations that are
reproductively isolated from other groups

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Mechanisms of Evolution
Genetic Drift
Mutation
Gene flow
N d tiNon random mating
Natural Selection
Population Genetics (PopGen)
Study of behavior of genes in the
population
Genetics + Evolution
Mendel (1866); Darwin and WallaceMendel (1866); Darwin and Wallace
(1858)
Population Genetics
Evolution
- A change in the frequency of alleles in a
population over time
1000 garden peas; 2000 alleles (TT, Tt or tt)
T= 1000; t= 1000 freq of each allele= 0.5
What happens when
a. T inc; t dec?
b. T dec; t inc?
c. Freq does not change
Hardy-Weinberg Equilibrium
Frequency of alleles will remain the same
under the following conditions:
1. Size of population is large
2 No mutations2. No mutations
3. No migrations
4. Mating is random
5. Natural selection does not take place

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Genetic Drift
- Change of frequency of alleles over time
due to chance
a. Bottleneck effect
- occurs when a catastrophic eventp
drastically and nonselectively reduces
size of population
b. Founder effect
- small no. of individuals colonize a new
area
Mutations
Alter the nucleotide sequence of genes
May give an selective advantage in a
particular environment
eg Tolerance to a toxic metaleg. Tolerance to a toxic metal

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Gene Flow
Movement of alleles form one population
to another
Pollen, seeds, fruits
Runners or horizontal stemsRunners or horizontal stems
Mating is random
Individuals mate without regard to
genotype
Nonrandom mating
Self fertilization- Self fertilization
- Assortative mating- outcome of
pollinator preference
eg. Hawkmoths prefer to feed on flowers
with long corolla tube
Natural selection
Thomas Malthus
- Population of organisms tend to
increase geometrically
Geometric progression:- Geometric progression:
2,4,8,16,32,64…
- Resources are limited
Individual variation within
species
Mutation
Crossing over
Recombination
TTransposons
- DNA sequences
- have the ability to move from place to
place in chromosomes

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Natural selection
Individuals that are best adapted to their
environment have the greatest chance
of surviving and successfully
reproducingp g

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Certain traits that are common among
individuals
- provide superior adaptation in
environmentenvironment
Less common traits- do not confer
selective advantage
Tropical Forests
Lack of wind
Low light intensity
Pl tPlants
- Undivided leaves, large, with acumen
Competition for resources is NOT
necessary for natural selection to occur
Natural selection may occur if certain
individuals produce more offspring thanindividuals produce more offspring than
others

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Modes of natural selection
Stabilizing selection
- eliminates extreme phenotypes
Directional selection
- shifts the average or typical in one direction
by favoring one of the extreme phenotypesy g p yp
- leads to ANAGENESIS or phyletic evolution
Diversifying selection
- splits a population into 2 parts favoring both
extremes of phenotypic range
- leads to CLADOGENESIS or branching
evolution
Artificial selection
Selectively breeding plants or animals to
favor the production of offspring with
desirable traits

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Evolution can occur rapidly
Punctuated equilibrium
Eldredge and Gould, 1972
punctuated with short periods of rapid
changechange
Few year or thousand of years
eg.
-Colonization of mine tailings by plants
Co-evolution
a change in the genetic
composition of one species in
response to a genetic change
in another
Plants and insects
Speciation
Formation of new species from preexisting
species
Ultimate result of evolution
Biological Species ConceptBiological Species Concept
- A population whose members have the
potential to interbreed with one another in
nature to produce viable, fertile offspring but
who cannot produce viable, fertile offspring
with members of other species
- Reproductively isolated from other populations
Reproductive isolation
Prezygotic
- Sperm does not fertilize egg from other
population
No zygote is formed- No zygote is formed
Postzygotic
- Zygote or embryo does not survive or
adult is infertile

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Prezygotic
Temporal isolation
Seasonal
Diurnal
Ecological – eg. Acer
black maple (Acer nigrum)- dry, high Cablack maple (Acer nigrum) dry, high Ca
sugar maple (A. saccharum)- acidic
Self fertilization
Floral
Behavioral- restriction to one pollinator
Structural – white and red petaled flower
Pollen-pistil incompatibility
Post zygotic
Inviable seed
Hybrid inviability- not reach reproductive
maturity
Hybrid floral isolation – no pollinators
Hybrid sterility
Chromosomes do not pair during meiosis
Brocolli (Brassica oleracea) x radish (Raphanus
sativus) Raphanobrassica
Hybrid breakdown- problems in later
generation of hybrids
Modes of speciation
Allopatric speciation
Geographical barrier that physically isolates
populations hinders gene flow
Sympatric speciationSympatric speciation
Intrinsic factors alter gene flow
Allopatric speciation
geographical barriers: mountain range,
oceans, lakes, creeping glaciers
Adaptive radiation
When a species move into previously- When a species move into previously
unoccupied environment (island or
occupied environment with many
opportunities to succeed)
- Scalesia spp. in Galapagos Islands

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Sympatric Speciation
Occurs within the range of parent
populations
Polyploidy
- more than 2 complete sets ofp
chromosomes; common in plants
- oats, cotton, potatoes, tobacco, wheat
a. Autopolyploid- from single species
b. Allopolyploid- 2 different species
- more vigorous than parents