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EVOLUTION
Prof. Benilda Ramos-Butron
What is evolution?
• Refers to changes in the populations,
species or groups of species
• Variation of the frequency of heritable traits
that appear from one generation to the
next
• Changes in allele frequencies over time
Two areas of evolutionary study
1. Microevolution
• Describes the details of how
populations of organisms change from
generation to generation and how new
species originate
2. Macroevolution
• Describes patterns of changes in
groups of related species over broad
periods of geologic time
• Determines phylogeny
Evidence of Evolution
1. Paleontology – provides fossils that
reveal the prehistoric existence of extinct
species
2. Biogeography – uses geography to
describe the distribution of species
3. Embryology – reveals similar stages in
ontogeny among related species
4. Comparative anatomy – describes two
kinds of structures that contribute to the
identification of evolutionary relationship
among species
• Homologous structures
• Analogous structures
Evidences of Evolution
5. Molecular Biology/Biochemistry –
examines the nucleotide and amino acid
sequences of DNA and proteins from
different species
Earliest Advocates of
Evolutionary Ideas
1. Jean Lamarck
• Use and disuse
• Inheritance of acquired characteristics
• Natural transformation of species
2. Charles Darwin
• Theory of Natural Selection or known
as the “survival of the fittest”
3. Neo-Darwinism or Synthetic Theory of
Evolution or Modern Synthesis
Explain the difference of the
theories of Lamarck and
Darwin given the illustration
that follows.
Natural Selection
• Is the difference in survival and reproduction
among individuals in a population as a result of
their interaction with the environment
• Arguments of Darwin for Natural Selection
 Population possess an enormous reproductive
potential
 Population size remains stable
 Resources are limited
 Individuals compete for survival
 There is variation among individuals in a
population
 Much variation is heritable
 Only the most fit individuals survive
 Evolution occurs as advantageous traits
accumulate
Kinds of Selection According to
Darwin
1. Stabilizing selection
2. Directional selection
3. Disruptive selection or Diversifying
selection
Sources of Variation
1. Mutations – provide the raw material for
new variation
2. Sexual reproduction – creates individuals
with new combinations of alleles
• Crossing over, independent
assortment and random joining of
gametes
3. Diploidy
4. Outbreeding – mating with unrelated
partners
5. Balanced polymorphism – is the
maintenance of different phenotypes in a
population
• Heterozygote advantage, hybrid vigor,
frequency adapted selection
Causes of Changes in Allele
Frequencies
1. Natural Selection – is the increase or
decrease in allele frequencies due to the
impact of the environment
2. Mutations – introduce new alleles that
may provide a selective advantage
3. Gene flow – describes the introduction or
removal of alleles from the population
when individuals emigrate or immigrate
4. Genetic drift – random increase or
decrease of alleles
• Founder effect
• Bottleneck
Causes of Changes in Allele
Frequencies
5. Nonrandom mating – occurs when
individuals choose mates based upon their
particular traits
• Inbreeding
• Sexual selection
Interpret the diagram that
follows regarding speciation.
Speciation
• Formation of new species
• Processes:
 Allopatric speciation – begins when a
population is divided by a geographic
barrier
 Sympatric speciation – is the formation
of new species without the presence of
a geographic barrier (balanced
polymorphism, polyploidy, hybridization)
 Adaptive radiation – is the relative rapid
evolution of many species from a single
ancestor
Patterns of Evolution
Patterns of Evolution
1. Divergent Evolution – describes two or
more species that originate from a
common ancestor
2. Convergent Evolution – describes two
unrelated species that share similar traits
3. Parallel Evolution – describes two
unrelated species or two related lineages
that have made similar evolutionary
changes after their divergence from a
common ancestor
Patterns of Evolution
4. Coevolution – is the tit-for-tat evolution of
one species in response to new
adaptations that appear in another species
The Origin of Life
•
•
Chemical evolution – is the study how life
began
Heterotroph theory – proposes that he
first cells were heterotrophs
SUCCESSION:
1. The earth and its atmosphere formed
• Primordial atmosphere consisted of
CO, CO2, H2, N2, H2O, S, HCl and
HCN but little or no oxygen
The Origin of Life
2. The primordial seas formed.
3. Complex molecules were synthesized
• Formation of organic soup (acetic acid,
formaldehyde, amino acids)
• Energy provided from UV, lightning,
radioactivity, and heat
• A.I. Oparin and J.B.S. Haldane
proponents of an oxygen-less primitive
atmosphere
• Stanley Miller performed experiment to
prove Oparin and Haldane’s theory
The Origin of Life
4. Polymers and self-replicating molecules
were synthesized
• Proteinoids – abiotically produced
polypeptides
5. Organic molecules were concentrated and
isolated into protobionts
• Protobionts – precursors of cells
• Microspheres and coacervates
6. Primitive heterotrophic prokaryotes formed
7. Primitive autotrophic prokaryotes were
formed
The Origin of Life
8. Oxygen and the ozone layer formed and
abiotic chemical evolution ended
9. Eukaryotes formed (Endosymbiotic theory)
In the present day, do you think
evolution happens? If yes, what
factors do you think pushes
evolution of organisms?
The End