Introduction to Darwinian Evolution

Moises Von Rosauro R. De Gracia

BSE - III

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.

Ideas About Evolution

O427-347 B.C. Plato’s divinelyinspired “ideal form”

O384-322 B.C. Aristotle’s “Ladder ofNature”O Aristotle visualized organisms as being

imperfect “moving toward a more perfectstate”

O1700s CreationismO Each species was created individually

by GodO Earth was the center of the universeO Man stood atop creation

O Leonardo Da Vinci (1452 – 1519)O The first to interpret the unusual finding

of animals in the rocks high onmountain.

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 acceptedO Did not provide a mechanism for evolutionO Earth was not old enough to allow time for

the process of evolution

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)

O 1726-1797 James Hutton

O developed uniformitarianism –

gradual change

O 1797-1875 Charles Lyell’s

O “Old Earth Hypothesis” supported

Hutton, gave time for gradual

change

O 1809-1882 Charles Darwin

O Developed the theory of evolutionO Species evolved through natural selection;

O Adaptation to their ever-changing environment

O 1823-1913 Alfred Wallace

O supported Darwin's theory (workedseparately, came up with sameconclusion, came in “2nd”)

EVOLUTION:The genetic makeup of the population changes over time, driven by natural selection

NATURAL SELECTIONOn average, the fittestorganisms leavethe most offspring

Competition for survival and reproduction

Potential forrapid reproduction

Relatively constantresources andpopulation over time

Variability instructures and behaviors

Some variability is inherited

(observations)

(conclusions)

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

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.

• The history of life is like a tree.

• The Linneanclassificationschemereflected thebranchinggenealogy of thetree of life, withorganisms at thedifferent levelsrelated throughdescent fromcommonancestors.

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.

• e.g. Darwin’s finches ADAPTIVE

RADIATION

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

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.

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.

• 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

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

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.)

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

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

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

Evidences of Evolution

O Fossils

O Comparative Anatomy

O Comparative Embryology

O Comparative Biochemistry

Fossils

O Transitional forms are evidence ofevolutionary change

O Fossils of ancient species tend to besimpler in form than modern species

O Several series of fossils have beenfound that exhibit the evolution ofbody structures over time

Interpretation of fossil data controversial

ODating of fossils

ODo fossils really show transitional forms?

Information about Fossils

Fossils of Extinct Organisms

Comparative Anatomy

O Homologous structuresO structures that have the same evolutionary

origin despite their current appearance or function

O Analogous structuresO structures that are outwardly similar in

appearance, but differ in their evolutionary origin

O Vestigial structuresO remnants of structures that are inherited from

ancestorsO Had important functions in ancestorsO Serve no obvious purpose in present day

organism

Analogous Structure

Not homologous;

not analogous

Homologous;

not analogous

Not homologous;

analogous

Homologous;

analogous

Homologous Structure

Flying Swimming Running Grasping

Vestigial Structure

Comparative Emryology

O Early vertebrate embryos

similar

O Tail and gill arches

Comparative Embryology

Comparative Biochemistry

O All have DNA, RNA, ribosomes, ATP,

etc.

O DNA similarities