Development of
Evolutionary
Thought
Isn’t evolution “just” a
theory?
•Scientific theories are explanations
that are based on lines of evidence,
enable valid predictions, and have
been tested in many ways.
Evolve – change over
time
What is Evolution?
 Evolution
- a change in
the genetic composition
of a population over time.
Paleontology & Evolution
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Older layers of sedimentary rock (the
layers on the bottom) contain fossil
species very dissimilar from modern life.
Each layer (stratum) is characterized by
a unique group of fossil species.
As you move upward through the
layers, you find species more and more
similar to modern life.
James Hutton - 1795
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A Scottish geologist
proposed that it was possible to explain
the various landforms by looking at
mechanisms currently operating in the
world
Proposed that the earth was much
more than a few thousand years old
Jean Baptiste Lamarck


Theory of evolution in 1809
mechanism:
– use and disuse - the idea that the parts
used the most grow stronger; the parts
that don’t get used deteriorate
– inheritance of acquired characteristics - the
modifications that an organism acquires
during its lifetime can be passed along to
its offspring

recognized adaptation to environment
as a primary product of evolution
Charles Darwin (1809-1882)
Father of modern
evolutionary theory
 Born in England
 HMS Beagle
 Galapagos Islands

The Galapagos Finches
What is an adaptation?

An inherited characteristic that
increases an organism’s ability to
survive and reproduce in its specific
environment.
Darwin’s Observations
Darwin noticed that every bird on the
Galapagos Islands was a modified finch.
 The only differences in the birds were their
beaks and what they ate.
 These finches looked very similar to one
type on South American continent, but none
of these were found in S.A.
“How did one species change into a different
species?”

He wrote On The Origin of
Species (1859) after 20
years of study.
Darwin’s Four Postulates
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Individuals within a population vary in
their traits.
Some of these traits are heritable.
More offspring are produced than can
survive because of limited resources.
Individuals with advantageous traits
will survive and reproduce.
What is natural selection?


Natural selection - a population of
organisms can change over
generations if individuals having
certain heritable traits leave more
offspring than others
Natural selection is the mechanism
by which evolution is proposed to
occur
What is “artificial
selection”?



Nature provides the variation among
different organisms, and humans
select variations that they find useful.
Example: breeding cows, horses,
hogs
Darwin used this to help support his
case for natural selection.
Descent with modification
the history of life is like a tree, with
multiple branching and re-branching from
a common trunk all the way to the tips of
the youngest twigs
most branches of evolution are dead
ends; about 99% of all species that have
ever lived are extinct
Figure 22.7 Descent with modification
Survival of the Fittest
•
Another name for Darwin’s theory of
natural selection.
•Biologists use the word fitness to
describe how good a particular
genotype is at leaving offspring in the
next generation relative to how good
other genotypes are at it.
Mechanisms of
Evolution
Natural Selection &
Survival of the Fittest
(already discussed with Darwin)
Modern Ideas

Darwin + Mendel’s work and the work
of others, have lead to modern ideas
about evolution.
Another mechanism of evolution is
Genetic Drift (random changes in
genes) which occurs through natural
selection.
Modern Ideas

Speciation – formation of new species is
due to gradual genetic changes, and that
large scale evolution is the result of a lot of
small scale evolution.

Microevolution – process responsible
for the variations that exist within a species,
or a change in the allele frequency.
Modern Ideas


Macroevolution – evolution that
occurs between species.
Examples: the separation of a species
to form two distinct species or the
development of a new species from
many small changes within an existing
species
Gene Flow

The change in occurrence of genes in
a population. This occurs when an
individual leaves a population
(emigration) or new individual joins a
population (immigration).
Genetic Drift
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Random changes in the occurrence of genes
through chance events.
Can occur when a few individuals of a
population break off from the original group
and start their own population (founder
effect).
Large number of population is killed due to
disease, starvation, natural disaster, etc.
(bottle necking)
Punctuated Equilibrium
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Darwin felt that biological change was slow
and steady as indicated in the fossil record.
Modern scientists see that this pattern does
not always hold. (Darwin’s finches)
The term punctuated equilibrium is used to
describe a pattern of long, stable periods
interrupted by brief periods of more rapid
change. This is still controversial today.
Evidence of
Evolution
Fossil Evidence


Fossils provided a detailed record of
evolution.
Fossils formed in different layers of
rock were evidence of gradual change
over time.
Homologous Body
Structures

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Structures in different species that may
perform different functions but are
similar because of their common
ancestry
Vestigial organs - structures of no
apparent function to an organism;
leftover from ancestry; ex - snakes
have leg & pelvis bones
Figure 22.14 Homologous structures: anatomical signs of descent with
modification
More homology…

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Molecular homology - similarity in DNA
sequence between an ancestor and its
progeny
Embryological homology - similarities
only apparent in embryological
development
– ex: all vertebrate embryos have
“pharyngeal pouches” which later become
gills or Eustachian tubes
Patterns of
Evolution
Adaptive Radiation


When a single species or a small group
of species has evolved into several
different forms that live in different
ways.
Example: Darwin’s finches (more than
a dozen evolved from a single species)
Convergent Evolution

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Explains how unrelated species can
develop similar characteristics
Porpoise (mammal) & Shark (fish)
Unrelated animals, but share similar
characteristics to suit their
environment
Analogous structures

Show similarity in structure based
on adaptation for the same
function, not common descent.
Divergent Evolution
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Suggests that many species develop
from a common ancestor
Penguins (wings for swimming) &
vultures (wings for flying)
Both are birds, diverged from a
common ancestor
Co-evolution

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When two or more organisms in an
ecosystem evolve in response to each
other.
Example: Flowers and their pollinators
Camouflage – an animal
looks like its environment.

http://rainforests.mongabay.com/0306
.htm
Mimicry- when animals have
coloring and markings to
look like another animal