1. Evidence for evolution comes from fossil records, homologous structures, biogeography, and genetics. Fossil records show changes within groups over time, including the origin of new groups and extinction of species. Homologous structures indicate common ancestry. Biogeography, based on patterns of species distribution, allows inferences about when and where groups evolved. 2. Darwin proposed natural selection to explain evolution. He observed variation within populations, inheritance of traits, overproduction of offspring exceeding environmental carrying capacity, and differential survival based on heritable traits. This leads to accumulation of favorable traits and adaptation to the environment over generations. 3. Isolation of populations through geographic or reproductive barriers can lead to allopatric or symp

1. EVOLUTION
BY NATURAL
SELECTION

2. ORIGIN OF
IDEAS
ABOUT
ORIGINS
Different
kinds of
evidence
exist:
How do we know that
things changed?...
Evidence found in:
• Fossil records
• Modification by descent
and Homology
• Biogeography
• Genetics

3. 1. Fossil records
• Fossils  remains or
traces of organisms
from the past,
• Fossil record 
evidence of
• extinction of
species,
• origin of new
groups,
• changes within
groups over time

4. 2. Modification by
descent and
homology
•Homologous
structures 
anatomical
resemblances  any
characteristic that
originated through
evolution from a
common ancestor.

5. Mammalian forelimbs:
homologous structures

6. CONVERGENT
EVOLUTION…
•Convergent evolution 
independent evolution of
similar features in species of
different lineages.
•Convergent evolution creates
analogous structures that
have similar form / function,
but not present in last
common ancestor of those
groups.

7. CONVERGENT EVOLUTION

8. 3. biogeography
•Earth’s continents were formerly united in
single large continent  Pangaea 
separated by continental drift.
•Islands have many endemic species that are
often closely related to species on nearest
mainland / island.
•Understanding continent movement &
modern distribution of species allows us to
predict when & where different groups
evolved.

9. hypothesis VS
theory
• Hypothesis  tentative answer to well-
framed question,
• narrower in scope than theory &
subject to testing.
• Theory  explanation broad in scope,
• supported by a large body of
evidence.

10. Overview of the history of different
theories of development
•Spontaneous creation
•Ontogeny
•Lamarckism
•Neo Darwinism
•Punctuated Equilibrium

11. Theory of
spontaneous
creation/
generation
• Spontaneous generation  complex,
living organisms produced from non-
living matter.
• Popular belief that mice occur
spontaneously from stored grain, or
maggots spontaneously appear in
meat.

12. The theory of
ontogeny
•Origin &
development of
individual organism
from embryo 
adult.
•Developmental
history of
organism within
own lifetime,

13. Lamarckism
•Species evolve through
•use & disuse of body
parts

15. Neo
Darwinism
• Darwinism as
modified by findings
of modern genetics,
• mutations due to
random copying
errors in DNA
cause variation
within population
• natural selection
acts upon these
variations.

16. Punctuated
equilibrium
• The fossil record  examples of
species
• appear suddenly, persist
unchanged for some time, and then
apparently disappear
• periods of apparent stability
punctuated by sudden change

17. CHARLES DARWIN
THE FATHER OF EVOLUTION

18. BEAK VARIATION IN GALAPAGOS FINCHES

19. Artificial selection
•Darwin noted humans modify other
species by
•selecting & breeding individuals with
desired traits 
•artificial selection.

20. These different
vegetables have
all been selected
from 1 species of
wild mustard. by
selecting
variations in
different parts of
the plant,
breeders have
obtained these
divergent results.

21. Darwin
described 4
observations
of nature &
from these
drew 2
inferences
(conclusions)
1. Observation 1: Members
of population often vary
greatly in their traits.
2. Observation 2: Traits are
inherited from parents 
offspring.
3. Observation 3: All species
are capable of producing
more offspring than
environment can support.
4. Observation 4: lack of
food or other resources,
many of offspring do not
survive.

22. Inference (conclusion) 1: 
inherited traits give them 
higher probability of surviving &
reproducing in a given
environment tend to have more
offspring than other individuals.
Inference (conclusion) 2: 
unequal ability of individuals to
survive & reproduce lead to
accumulation of favourable traits
in population over generations.

23. Natural
selection
• Individuals with certain heritable
characteristics survive & reproduce at
higher rate than other individuals
• Natural selection increases the
adaptation of organisms to environment
over time
• If an environment changes over time,
natural selection may result in
adaptation to these new conditions and
may give rise to new species

24. •Individuals do not evolve 
populations evolve over time
•Natural selection can only increase or
decrease heritable traits in a
population
•Adaptations vary with different
environments.

25. FORMATION OF NEW SPECIES
• Speciation: origin of new
species.
• Microevolution 
adaptations that evolve
within population confined
to 1 gene pool
• Macroevolution 
evolutionary change above
species level (genus,
family, order…)

26. BIOLOGICAL SPECIES
CONCEPT
• defines a species
taxon as a group
of organisms that
can successfully
interbreed and
produce fertile
offspring

27. speciation
The process that
results in new
species, occurs
when ancestral
population splits
into 2+ descendant
species that are
genetically distinct
and unable to
interbreed
• Speciation can
occur in two ways:
• Allopatric
speciation
• Sympatric
speciation

28. Allopatric
speciation
•In allopatric speciation 
geographic isolation restricts
gene flow between
populations
•BARRIER  INHIBIT ability
of a population to disperse.
•Separate populations may
evolve independently through
mutation, natural selection

29. Allopatric speciation
of antelope squirrels
on opposite rims of
the Grand Canyon
• Regions with many geographic
barriers typically have more
species than do regions with
fewer barriers
• Reproductive isolation between
populations generally increases
as the distance between them
increases.

30. sympatric speciation
•Speciation takes place in geographically
overlapping populations where a
reproductive barrier isolates a subset of
a population.
•can also result from appearance of
new ecological niches

31. reproductive
isolation
•Existence of biological factors
(barriers) that prevent 2
species from producing
viable, fertile offspring.
•Hybrids are the offspring of
crosses between different
species

32. Mechanisms
of
reproductive
isolation
• Breeding at different times of the year
• Species specific courtship behaviour
(animals)
• Adaptation to different pollinators
(plants)
• Incompatibility of external reproductive
organs (mating)
• Prevention of embryonic development
• Prevention of fertilisation
• Infertile offspring

33. Evolution in
present times
•Important example of
natural selection and
evolution:
•HIV resistance to anti-
retrovirals

34. HIV resistance to
anti-retrovirals
• The use of drugs to combat HIV selects for viruses resistant to these
drugs.
• HIV uses the enzyme reverse transcriptase to make a DNA version of its
own RNA genome.
• The drug 3TC is designed to interfere and cause errors in the
manufacture of DNA from the virus.
• Some individual HIV viruses have a variation that allows them to
produce DNA without errors.
• These viruses have a greater reproductive success and increase in
number relative to the susceptible viruses.
• The population of HIV viruses has therefore developed resistance to
3TC
• The ability of bacteria and viruses to evolve rapidly poses a challenge to
our society.