The document discusses the theory of biological evolution, including key concepts such as common ancestry, genetic variation over generations, natural selection, and speciation leading to diversity of life. It covers Darwin's theory that natural selection is the mechanism of evolution. Later, molecular analysis of genetic sequences helped map phylogenetic trees to show evolutionary relationships between organisms and domains of life more accurately.

1. The Theory of
Biological
Evolution

2. The Theory of Evolution, defined:
“All living species are descendants of
ancestral species and are different from
present day ones due to the cumulative
change in the genetic composition of a
population”
– Sooo in a nutshell, populations of living
things look and behave differently because
over time, their DNA has changed… but how?

3. Charles Darwin (1809-1882)
• Father of the theory of Evolution.
• Suggested that natural selection is the
mechanism by which species evolve over
geologic time.
• Proposed Descent with Modification:
– All organisms on Earth are related
through some unknown ancestral
type that lived long ago.

4. History of the Theory
• Evolutionary theory was developed
through many generations of scientists
interpreting new evidence to refine and
expand our understanding of biological
change across time.
– Darwin and Wallace (Evolution)
– Gregor Mendel (Genetics)
– Franklin, Watson & Crick (Genetics)

5. The Nuts and Bolts of Evolution
• Evolution: A cumulative change in the
inherited characteristics of population.
• Population!! Is what changes.
• Evolution is like a tree – many branches
emerged from a common beginning, some
branches died off (extinction), others
branched multiple times (present-day
diversity)

6. The Nuts and Bolts of Evolution
• The great diversity of living organisms is the
result of over 3.5 billion years of evolution, filling
every available niche with life forms.
• Niche: The area within a habitat occupied by an
organism OR the ecological role of an organism
within its community.

7. The Origin of Species
Darwin developed
two main ideas:
– Evolution
explains life’s
unity and
diversity
– Natural
selection is a
cause of adaptive
evolution

8. To Darwin, the history of life is like a tree.
multiple branchings from a common trunk to
the tips of the youngest twigs that represent
the diversity of living organisms
Figure 22.7
Hyracoidea
(Hyraxes)
Sirenia
(Manatees
and relatives)
Elephas
maximus
(Asia)
Loxodonta
africana
(Africa)
Loxodonta
cyclotis
(Africa)

9. The Six Main Points of
Darwin’s Theory of Evolution
Observations and Inferences

10. 1. Overproduction*
• Most species produce far more offspring
than are needed to maintain the
population.
• Species populations remain more or less
constant (“stable”) because a small
fraction of offspring live long enough to
reproduce.

11. 2. Competition*
• Living space and food are limited, so
offspring from each generation must
compete among themselves in order to
live.
• Only a small fraction can possibly survive
long enough to reproduce.

12. 3. Genetic Variation*
• Characteristics in individuals in any
species are not exactly alike.
– Ex: Differences for Homo sapiens (humans) can be
exact size or shape of body, strength in running, or
resistance to disease.
• These differences are considered to be
the variations within a species. What
causes slight variations between
individuals?

13. 4. Adaptation
An adaptation is an inherited trait that increases
an organisms’ chance of survival and
reproduction in a given environment.

14. 5. Natural Selection*
• Nature/environment selects for living
organisms with better suited inherited
traits to survive and reproduce.
• Variation caused by
within a species (ex: giraffe) may make
them better “equipped” for survival.
• Offspring inherit these better traits, and as
a whole the population improves for that
particular environment.

15. 5. Natural Selection, cont.
• Natural Selection does not move in a pre-
determined direction! The changing earth
determines what will and can survive.

16. 6. Speciation
• Over many generations, favorable adaptations
(in a particular environment) gradually
accumulate a in species and “bad” ones (in a
particular environment) disappear.
• Eventually, accumulated changes become so
great, the result is a new species.
• Formation of a new species is called
“Speciation” and it takes many, many
generations to do.

17. The four factors*
1. Overproduction
2. Competition
3. Genetic Variation
4. Natural Selection
Biological Evolution is a consequence of these
4 factors - they work together to impact any
living population

18. Which one of Darwin’s Six
Points do the following
pictures show?

19. Diagram 1

20. Diagram 2

21. Diagram 3

22. Diagram 4

23. Competition
or
Overpopulation

24. Variation

25. Speciation

26. Adaptation

27. Molecular Perspective
• One of the great breakthroughs in
research on the tree of life occurred when
American biologist Carl Woese
(pronounced woze) and colleagues began
analyzing the molecular components of
organisms as a way to understand their
evolutionary relationships.

28. Molecular Perspective
• Their goal was to understand the phylogeny of all
organisms—their actual genealogical
relationships.
• Translated literally, “phylogeny” means “tribe-
source.”
• To understand which organisms are closely versus
distantly related, Woese and co-workers needed
to study a molecule found in all organisms. They
selected an RNA molecule, an essential part of
the machinery that all cells use to grow and
reproduce (No technology to analyse DNA).

29. Analysing Genetic Variation
• Why might DNA (or RNA) be useful for understanding
the relationships between organisms?
• The answer is that the sequence of building blocks in
DNA is a trait that can change during the course of
evolution.
• Although a gene may code for an RNA or protein
molecule that performs the same function in all
organisms, the corresponding DNA sequence is not
identical among species.

30. How is such genetic variation
analyzed?
• Recall that the building blocks in DNA are symbolized by
the letters A, T, C, and G.
• Biologists use this letter code to depict DNA sequences.
• In land plants, for example, a section of DNA might start
with the sequence A-T-A-T-C-G-A-G.
• In green algae, which are closely related to land plants,
the same section of the molecule might contain A-T-A-T-
G-G-A-G.
• But in brown algae, which are not closely related to
green algae or to land plants, the same part of the
molecule might consist of A-A-A-T-G-G-A-C.

31. How is such genetic variation
analyzed?
• The next step in analyzing genetic
variation is to consider what the similarities
and differences in the sequences imply
about relationships between species.
• The goal is to produce a diagram that
describes the phylogeny of the organisms
being compared.

32. Phylogenetic tree
• A diagram that depicts evolutionary history in this way is
called a phylogenetic tree.
• Just as a family tree shows relationships between
individuals, a phylogenetic tree shows relationships
between species.
• On a phylogenetic tree, branches that share a recent
common ancestor—that is, an ancestral population—
represent species that are closely related;
• Branches that don’t share recent common ancestors
represent species that are more distantly related.

33. PHYLOGENY

45. Phylogenetic tree
• The tree includes such a diverse array of
species, it is often called the universal tree, or
the tree of life.
• Notice that the tree’s main node is the common
ancestor (ancestral population) of all living
organisms.
• Researchers who study the origin of life propose
that the tree’s root extends even further back to
the “last universal common ancestor” of cells,
or LUCA.

46. Single cell to multi cell
• The tree of life implied by genetic sequence data
established that there are three fundamental groups or
lineages of organisms:
• (1) the Bacteria, (2) the Archaea, and (3) the Eukarya.
• In all eukaryotes (literally, “true kernel”), cells have a
prominent component called the nucleus.
• Because the vast majority of bacterial and archaeal cells
lack a nucleus, they are referred to as prokaryotes
• The vast majority of bacteria and archaea are unicellular
(“one-celled”); many eukaryotes are multicellular (“many-
celled”).

47. Eukaryotes Prokaryotes

49. Classification system in biology
• When results based on genetic data were first published,
biologists were astonished.
For example: Prior to Woese’s work and follow-up
studies, biologists thought that the most fundamental
division among organisms was between prokaryotes and
eukaryotes.
The Archaea were virtually unknown—much less
recognized as a major and highly distinctive branch on the
tree of life.
• Fungi were thought to be closely related to plants.
Instead, they are actually much more closely related to
animals.

50. Classification system in biology
• Traditional approaches for classifying
organisms—including the system of five
kingdoms divided into various classes,
orders, and families that you may have
learned in high school—are inaccurate in
many cases, because they do not reflect
the actual evolutionary history of the
organisms involved.

51. How Should We Name Branches
on the Tree of Life?
• In science, the effort to name and classify organisms is
called taxonomy.
• Any named group is called a taxon (plural: taxa).
• Currently, biologists are working to create a taxonomy,
or naming system, that accurately reflects the phylogeny
of organisms.
• Based on the tree of life, Woese proposed a new
taxonomic category called the domain.
• He designated the Bacteria, Archaea, and Eukarya as
the three domains of life.

52. How Should We Name Branches
on the Tree of Life?
• Biologists often use the term phylum (plural: phyla) to
refer to major lineages within each domain.
• Although the designation is somewhat arbitrary, each
phylum is considered a major branch on the tree of life.
• Within the lineage called animals, biologists currently
name 30–35 phyla—each of which is distinguished by
distinctive aspects of its body structure as well as by
distinctive gene sequences.
• For example, the mollusks (clams, squid, octopuses)
constitute a phylum, as do chordates (the vertebrates
and their close relatives).