1) Evolution is the accumulation of genetic changes within populations over time through natural selection. It refers to changes in characteristics of populations over generations, not changes within individuals' lifetimes. 2) Early Greek philosophers like Plato and Aristotle proposed ideas about organisms changing over time, but creationism was dominant until the 1700s. Georges Buffon proposed evolution through natural processes. Jean-Baptiste Lamarck proposed the first natural mechanism of evolution. 3) Charles Darwin developed the theory of evolution by natural selection, proposing that species evolve through gradual adaptation to their environments and that all life shares common descent from early ancestors.

1. Introduction to
Darwinian Evolution
Moises Von Rosauro R. De Gracia
BSE - III

2. What is Evolution?
O Evolution is the accumulation of genetic
changes within populations over time.
O The term evolution does not refer to changes
that occur in an individual within its lifetime.
Instead, it refers to the changes in the
characteristics of population over the course
of generation.

3. Ideas About Evolution
B.C.
Plato’s
inspired “ideal form”
O 427-347
divinely
O 384-322 B.C. Aristotle’s “Ladder of
Nature”
O Aristotle visualized organisms as being
imperfect “moving toward a more perfect
state”

4. O 1700s Creationism
O Each species was created individually
by God
O Earth was the center of the universe
O Man stood atop creation
O Leonardo Da Vinci (1452 – 1519)
O The first to interpret the unusual finding
of animals in the rocks high on
mountain.

5. O 1707-1788 George LeClerc (Comte of
Buffon)
O creation provided a relatively small number
of founding species that evolved through
natural processes
O Idea was not accepted
O Did not provide a mechanism for evolution
O Earth was not old enough to allow time for
the process of evolution

6. O Jean Baptisté de Lamarck (1744-
1829)
O He was the first to propose that
organisms undergo change over time
as a result of some natural
phenomenon rather than divine
intervention.
O 1769-1832 G. Cuvier
O Theory of catastrophism (creationist
w/extinction)

7. O 1726-1797 James Hutton
O developed uniformitarianism –
gradual change
O 1797-1875 Charles Lyell’s
O “Old Earth Hypothesis” supported
Hutton,
change
gave
time
for
gradual

8. O 1809-1882 Charles Darwin
O Developed the theory of evolution
O Species evolved through natural selection;
O Adaptation to their ever-changing environment
O 1823-1913 Alfred Wallace
O supported
Darwin's theory (worked
separately, came up with same
conclusion, came in “2nd”)

9. Potential for
rapid reproduction
Relatively constant
resources and
population over
time
Competition for
survival and
reproduction
(observations)
(conclusions)
Variability in
structures and
behaviors
NATURAL
SELECTION
On average, the fittest
organisms leave
the most offspring
Some variability is
inherited
EVOLUTION:
The genetic makeup of the
population changes over
time, driven by natural
selection

10. Darwin’s Theory of Evolution
O Darwin’s Idea of Common Descent
O Darwin’s Idea of Gradualism
O Darwin’s Idea of Multiplication of
Species
O Darwin’s Idea of Natural Selection

11. Idea of Common Descent
• Evolution = descent with modification
• All organisms are related through descent
from some unknown ancestor that lived in
the distant past.
• As the descendants spilled into various
habitats over time, they accumulated
diverse modifications (adaptations) that fit
them to specific ways of life.

12. • The history of
life is like a tree.
• The
Linnean
classification
scheme
reflected
the
branching
genealogy of the
tree of life, with
organisms at the
different levels
related through
descent
from
common
ancestors.

13. Idea of Gradualism
• The origin of new species and adaptation
are closely related processes.
• A
new species would arise from an
ancestral form by the gradual accumulation
of adaptations to a different environment.
Darwin’s finches 
RADIATION
• e.g.
ADAPTIVE

15. Idea of Multiplication of Species
O The existence of an enormous number of
species
 some species are very similar (not as
distinct from each other!)
 gradual changes in various characteristics
as organisms became modified according to
the conditions in which they lived

16. Idea of Natural Selection
O Overproduction
O All species have a tendency and the potential
to increase at a geometric rate.
O Competition
O The conditions supporting life are limited.
O Only a fraction of the offspring in a population
will live to produce offspring, so that the number
of individuals in a population remains fairly
constant.

17. O Variation
O Individuals in a population vary greatly in their
characteristics.
O Adaptation
O Some variations enable individuals to produce
more offspring than other individuals.
O Natural Selection
O Individuals having favorable traits will produce
more offspring, and those with unfavorable
traits will produce fewer offspring.

18. • Speciation
O Given time, natural selection leads
to the accumulation of changes that
differentiate groups from one
another, such that a new species
may arise

19. Darwin’s Postulates on Natural
Selection
O Postulate 1
O Individual members of a population differ from
one another in many respects
O Variations arise purely by chance resulting from
random mutations in DNA
O Differences are obvious in many physical
characteristics and extend to molecular level

21. O POSTULATE 2
O At least some of the differences among
members of a population are due to
characteristics that may be passed from
parent to offspring
O However, the mechanism of inheritance
was not understood at this point in time
(Mendel was working at about the same
time…and was ignored until someone saw
that
Mendel
and
Darwin/Wallace
supported each other.)

22. O POSTULATE 3
O In each generation, some individuals in a
population survive and reproduce successfully
but others do not
O Darwin observed that many more
individuals are born than survive
O Some individuals have more offspring
than others

23. O POSTULATE 4
O Individuals with advantageous traits survive
longest and leave the most offspring, a process
known as natural selection
O Natural selection acts on individuals within
a population; however, it is the population
that changes over time

24. Patterns of Evolution
O Divergent evolution – from one species to
several different forms; adaptive radiation
O Convergent evolution – results in increased
resemblance between unrelated species
O Coevolution – occurs when two or more
species evolve in response to each other

25. Evidences of Evolution
O Fossils
O Comparative Anatomy
O Comparative Embryology
O Comparative Biochemistry

26. Fossils
O Transitional forms are evidence of
evolutionary change
O Fossils of ancient species tend to be
simpler in form than modern species
O Several series of fossils have been
found that exhibit the evolution of
body structures over time

27. Interpretation of fossil data
controversial
O Dating of fossils
O Do fossils really show
transitional forms?

28. Information about Fossils

29. Fossils of Extinct Organisms

30. Comparative Anatomy
O Homologous structures
O structures that have the same evolutionary
origin despite their current appearance or
function
O Analogous structures
O structures that are outwardly similar in
appearance, but differ in their evolutionary
origin
O Vestigial structures
O remnants of structures that are inherited from
ancestors
O Had important functions in ancestors
O Serve no obvious purpose in present day
organism

31. Analogous Structure
Not homologous;
analogous
Not homologous;
not analogous
Homologous;
not analogous
Homologous;
analogous

32. Homologous Structure
Flying
Swimming
Running
Grasping

33. Vestigial Structure

34. Comparative Emryology
O Early vertebrate embryos
similar
O Tail and gill arches

35. Comparative Embryology

36. Comparative Biochemistry
O All have DNA, RNA, ribosomes, ATP,
etc.
O DNA similarities