Evolution

1. Pre-Darwinian Ideas about Evolution
Evolution?
The term evolution is derived from
two Latin words – e
= from; volvere = to roll and means
the act of unrolling or unfolding,
Evolution is the accumulation of
inherited changes within a population
over time OR Evolution has been
defined as a gradual orderly change
from one condition to another
Pre-Darwinian Ideas about
Evolution
The historical development of evolutionary
thought:
Jean Baptiste de Lamarck was the first
scientist to propose that organisms undergo
change over time as a result of some natural
phenomenon rather than divine intervention.
Lamarck thought that organisms were
endowed with a vital force that drove them
to change toward greater complexity over
time. He thought that organisms could pass
traits acquired during their lifetimes to their
offspring.
Pre-Darwinian Ideas about Evolution

2. Pre-Darwinian Ideas about Evolution
Charles Darwin’s observations while
voyaging on the HMS Beagle were the
basis for his evolutionary theory.
Darwin tried to explain the similarities
between animals and plants of the arid
Galápagos Islands and the humid South
American mainland.
Charles Darwin (1859) has defined
evolution as "descent with
modification", i.e., closely related
species resembling one another because
of their inheritance and differing from
one another because of the hereditary
differences accumulated during the
separation of their ancestors
Darwin was influenced by artificial
selection, in which breeders develop
many varieties of domesticated plants
and animals in just a few generations.
Darwin applied Thomas Malthus’s ideas
on the natural increase in human
populations to natural populations.
Darwin was influenced by the idea that
Earth was extremely old, an idea
promoted by Charles Lyell and other
geologists.
Pre-Darwinian Ideas about Evolution

3. Evolution
Explain the four premises of evolution by natural
selection as proposed by Charles Darwin.
Charles Darwin and Alfred Russel Wallace
independently proposed evolution by natural
selection, which is based on four observations.
First, the reproductive ability of each species
causes its populations to have the potential to
geometrically increase in number over time.
Second, genetic variation exists among the
individuals in a population
Third, organisms compete with one another for the
resources needed for life, such as food, living
space, water, and light.
Fourth, offspring with the most favorable
combination of inherited characteristics are most
likely to survive and reproduce, passing those
genetic characteristics to the next generation.
Natural selection results in adaptations,
evolutionary modifications that improve the
chances of survival and reproductive success in a
particular environment.
Over time, enough changes may accumulate in
geographically separated populations to produce
new species.

4. Evolution
Darwin proposed that evolution occurs by natural selection
a. Overproduction
The reproductive ability of each species has the potential to
cause its population to geometrically increase over time. A
female oyster lays about 1,00000 eggs, and a female cod
produces perhaps 40 million eggs!
In each case, however, only about some offspring survive to
reproduce. Thus, in every generation each species has the
capacity to produce more offspring than can survive.
b. Variation
The individuals in a population exhibit variation. Each
individual has a unique combination of traits, such as size,
color, ability to tolerate harsh environmental conditions, and
resistance to certain parasites or infections. Some traits improve
an individual’s chances of survival and reproductive success,
whereas others do not.
Genetic variation in emerald tree boas
These snakes, all the same species (Corallus caninus), were caught in a
small section of forest in French Guiana.
Many snake species exhibit considerable variation in their coloration and
patterns.

5. Evolution
Darwin proposed that evolution occurs by natural selection
C. Limits on population growth, or a struggle for existence.
There is only so much food, water, light, growing space, and other
resources available to a population, so organisms compete with one
another for these limited resources.
Because there are more individuals than the environment can
support, not all survive to reproduce.
Other limits on population growth include predators, disease
organisms, and unfavorable weather conditions.
D. Differential reproductive success.
Those individuals that have the most favorable combination of
characteristics (those that make individuals better adapted to their
environment) are more likely to survive and reproduce.
Offspring tend to resemble their parents because the next generation
inherits the parents’ genetically based traits.

6. Evolution
Compare the modern synthesis with Darwin’s
original view of evolution.
The modern synthesis combines Darwin’s
evolutionary theory by natural selection with
modern genetics to explain why individuals in
a population vary and how species adapt to
their environment.
Mutation provides the genetic variability that
natural selection acts on during evolution.

7. Evolution
Evidence for Evolution
Summarize the evidence for evolution obtained
from the fossil record.
Direct evidence of evolution comes from fossils, the remains
or traces of ancient organisms.
Layers of sedimentary rock normally occur in their sequence
of deposition, with the more recent layers on top of the
older, earlier ones.
Index fossils characterize a specific layer over large
geographic areas.
Radioisotopes present in a rock provide a way to accurately
measure the rock’s age.
Index fossils (also known as guide fossils or indicator fossils)
are fossils used to define and identify geologic periods (or
faunal stages). Index fossils must have a short vertical range,
wide geographic distribution and rapid evolutionary trends.
Viviparus glacialis
Tiglian
(Early Pleistocene)
0.5 million years ago

8. Evolution
Define biogeography and describe how the
distribution of organisms supports evolution.
Biogeography, the geographic distribution
of organisms, affects their evolution.
Areas that have been separated from the
rest of the world for a long time contain
organisms that have evolved in isolation
and are therefore unique to those areas.
At one time the continents were joined to
form a supercontinent.
Continental drift, which caused the
various landmasses to break apart and
separate, has played a major role in
evolution.

9. Evolution - Evidences
Describe the evidence for evolution
derived from comparative anatomy.
Homologous features have basic
structural similarities even though the
structures may be used in different ways
because homologous features derive
from the same structure in a common
ancestor, i.e divergent evolution
Evolutionary affinities exist among the
organisms that have homologous
features.

10. Evolution - evidences
Describe the evidence for
evolution derived from
comparative anatomy.
Analogous features evolved
independently to have similar
functions in distantly related
organisms.
Analogous features demonstrate
convergent evolution, in which
organisms with separate ancestries
adapt in similar ways to comparable
environmental demands.

11. Evolution - EVIDENCES
Describe the evidence for evolution derived from comparative anatomy.
Vestigial structures are nonfunctional or degenerate remnants of structures that
were present and functional in ancestral organisms.
Structures occasionally become vestigial as species adapt to different modes of life.
all pythons have remnants of hind-limb bones
embedded in their bodies.

12. Evolution - evidences
Briefly explain how developmental biology provide
insights into the evolutionary process.
Development in different animals is controlled by the same
kinds of genes, which indicates that these animals have a
shared evolutionary history.
The accumulation of genetic changes since organisms
diverged, or took separate evolutionary pathways, has
modified the pattern of development in more complex
vertebrate embryos.
Development of fish fins, chicken wings, and human limbs
Fish, chickens, and humans are vertebrates with strikingly similar
genes. although the early embryos of these organisms are much
alike, the areas colored orange follow different developmental
pathways, resulting in fins, wings, or limbs.

13. Evolution - Evidences
Briefly explain how molecular biology provide insights into
the evolutionary process.
Molecular evidence for evolution includes the universal
genetic code and the conserved sequences of amino acids in
proteins and of nucleotides in DNA.
Evolutionary changes are often the result of mutations in
genes that affect the orderly sequence of events during
development.
Differences in DNA nucleotide sequences as evidence of
evolutionary relationships

14. Evolution- Microevolution
Microevolution is a change in allele or
genotype frequencies over time within a
population.
How each of the following micro
evolutionary forces alters allele frequencies
in populations: nonrandom mating, mutation,
genetic drift, gene flow, and natural selection.
In nonrandom mating individuals select
mates on the basis of phenotype, indirectly
selecting the corresponding genotype(s).
Inbreeding is the mating of genetically
similar individuals that are more closely
related than if they had been chosen at
random from the entire population.
Inbreeding in some populations causes
inbreeding depression, in which inbred
individuals have lower fitness (relative
ability to make a genetic contribution to the
next generation) than non-inbred individuals.

15. Evolution-Mechanisms of Evolution
In assortative mating individuals select mates
by their phenotypes. Both inbreeding and
assortative mating increase the frequency of
homozygous genotypes.
Mutations, unpredictable changes in DNA, are
the source of new alleles. Mutations increase
the genetic variability acted on by natural
selection.
Genetic drift is a random change in the allele
frequencies of a small population. Genetic drift
decreases genetic variation within a population,
and the changes caused by genetic drift are
usually not adaptive.
A sudden decrease in population size caused by
adverse environmental factors is known as a
bottleneck.
Genetic drift
Mutations

16. Evolution
The founder effect is genetic
drift that occurs when a small
population colonizes a new
area.
Gene flow, a movement of
alleles caused by the migration
of individuals between
populations, causes changes in
allele frequencies.
Natural selection causes
changes in allele frequencies
that lead to adaptation.
Natural selection operates on
an organism’s phenotype, but it
changes the genetic
composition of a population in a
favorable direction for a
particular environment.
Gene flow
Founder effect
Natural selection

17. Evolution
Distinguish among
stabilizing selection,
directional selection,
and disruptive
selection.
Stabilizing selection
favors the mean at
the expense of
phenotypic extremes.
Directional selection
favors one phenotypic
extreme over another,
causing a shift in the
phenotypic mean.
Disruptive selection
favors two or more
phenotypic extremes.
Selective Pressures
Selective pressures: External forces which
affect an organism’s ability to survive in a
given environment.
•Selection pressures can be negative
(decreases the fitness of a trait) or positive
(increases the fitness of a trait)
Examples of selection pressures:
Predators, availability of resources,
disease, accumulation of wastes, abiotic
factors (climate, CO2 levels), natural
disasters.
Looking at populations – we can see how
populations shift based on pressure. The
group shows the variation in a population
and the effect of pressure on populations
Directional Selection: The pressures favor
one “extreme” of the trait in a population.
Stabilizing Selection: If conditions stable
for a long time, pressure favors
“moderates”
Disruptive Selection: The pressure favors
both extremes as they both give benefits

18. Evolution
Genetic Variation in Populations
Describe the nature and extent of genetic variation, including
genetic polymorphism, balanced polymorphism, neutral
variation, and geographic variation.
Genetic polymorphism is the presence of genetic variation
within a population.
Balanced polymorphism is a special type of genetic
polymorphism in which two or more alleles persist in a
population over many generations as a result of natural
selection.
Heterozygote advantage occurs when the heterozygote
exhibits greater fitness than either homozygote.
In frequency dependent selection, a genotype’s selective value
varies with its frequency of occurrence.
Neutral variation is genetic variation that confers no
detectable selective advantage.
Geographic variation is genetic variation that exists among
different populations within the same species.
A cline is a gradual change in a species’ phenotype and
genotype frequencies through a series of geographically
separate populations.
Genetic polymorphism