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Evidence of Evolution
Emergence of Evolutionary Thoughts
A Theory Takes Form
Evidence from Fossils
Evidence in Body Form
Influential Geological Forces
Evolution: in the broadest sense of the term, refers to change
or growth that occurs in a particular order
In biology, evolution refers to the processes that have
transformed life on Earth from its earliest forms to the vast
diversity that we observe today/ heritable changes
Microevolution: generation-to-generation changes in a
population’s allelic or genotypic frequencies
Macroevolution: large-scale evolution occurring over very
long periods of time
At or above species level
Formation of new taxonomic groups
Aristotle (Ancient Greece):
species are fixed and do not
evolve
All forms of life arranged on a
scale of increasing complexity/
Continuum of organization
(Natural Scale of Life)
Insects and small animals were
at the bottom, and humans sat at
the top
19th Century Expeditions out of Europe
Extensive observations of nature in the 19th
century did not fit with the prevailing belief
systems
Cumulative findings from biogeography,
comparative morphology and geology led
naturalists to question the traditional ways of
interpreting the natural world
Biogeography
The study of patterns
in the geographic
Emu/ Australia
distribution of
species
Rhea/ South
America
Ostrich/ Africa
Comparative morphology
Ø The study of anatomical patterns
Ø Problematic in classifying organisms that are
outwardly very similar, but quite different otherwise/
reproductive parts
Vestigial structures
Ø  Body
parts that have no apparent function/ tail bones
in humans
Fossils
Ø Physical evidence of
organisms that lived in
the ancient past
Ø Deeper layers held
fossils of simple marine
life
Ø Layers above held
similar but more
complex fossils
George Cuvier
Ø Assumed
Earth to be
thousands, not billions of years
old
Ø Proposed
theory of
catastrophism to explain
extinction
Jean Baptiste Lamarck
Ø Advocated that life
evolves (changes in the line
of descent)
Ø Proposed that
environmental pressures
cause an internal need for
change
Ø Proposed inheritance of
acquired characteristics
Ø Change occurs through
use and disuse of body parts
Charles Darwin
The Voyage of the Beagle (1831-1836)/ expedition
to South America
Ø Observed and collected specimens of the
exotic and diverse faunas and floras of South
America
Ø Noted that the plants and animals on the
continent had very unique characteristics,
very distinct from those of Europe
Ø Species on the Galapagos islands are found
nowhere else in the world
Ø Species unique to different islands
Ø Species similar but not identical to species on
nearby mainland (but quite different from
animals on far mainland)
Charles Lyell: The
Principles of Geology
“Uniformity Theory”
“Gradualism” / Earth had
changed slowly, and what we
see today is the result of
gradual changes (over
millions of years)
Thomas Malthus
Ø Correlated decreases in the
size of human populations
with episodes of disease,
famine and war
Ø Proposed idea that humans
can run out of resources
Ø Human reproduction can
exceed capacity of
environment to sustain them
Back to Darwin
After the Voyage of the Beagle
Reassessed all observations made during the
voyage
By early 1840s, wrote a manuscript describing the
major features of his theory of evolution by natural
selection, but never published
Alfred Russel Wallace
Developed his theory
about evolution by
natural selection
independently from
Darwin based on his
work in Indonesia
(1858)
“On the Origin of Species by Means
of Natural Selection”
Charles Darwin (1859)
Darwin’s Theory of Evolution
Darwin’s main idea: living species have
descended from earlier life-forms and that
species change over time/
Descent with modification
Darwin proposed natural selection as the
mechanism by which evolution occurs
Natural selection occurs within populations
Individuals of natural populations vary in fitness/ degree
of adaptation to an environment, as measured by genetic
contribution to future generations
Results in adaptation of organisms within a population
to their environment
Adaptive trait: a heritable trait that enhances an
individual’s fitness to an environment
Natural selection can be defined as differential success in
survival and reproduction within a population
Fossils as Evidence of Evolution
Preserved remains of organisms that lived in
the past
Document the differences between past and
present organisms and the fact that many
species became extinct
Formed in different ways
Most fossils are mineralized bones, skulls, teeth
Casts or mold fossils:
Created when an organism is
buried and decays
The empty hole where the
organism was is filled in with
sediments or minerals
Trace Fossils:
Fossils of an organisms activity
Footprints, burrows, tracks
Some fossils retain
organic material
Ø Fossilized leaves
contain remnant
chlorophyll
Ø Insects in amber
(fossilized resin)
Petrification: remains of
dead organisms turned to
stone through the
replacement of the original
organic material with
minerals
Petrified tree
Fossil Record
History of life as documented
by fossils
The sequence in which fossils
appear within layers of
sedimentary rocks (the strata)
provides the strongest
evidence of evolution
Will never be complete
Ø geological events
Ø slanted toward species
with hard parts
How Is The Age of Rocks and Fossils
Measured?
Radiometric dating
Ø  Half-life: the
time it takes for
half of the atoms
in a sample of
radioisotope to
decay
How Has Earth
Changed Over
Geologic Time?
Continental Drift (1900’s)
Movement of the Earth's
continents relative to each
other by appearing to drift
across the ocean bed
250 million years ago, plate
movements brought all the
land masses together into a
supercontinent: Pangaea
180 million years later,
Pangaea broke apart
Plate Tectonics Theory (1950’s)
Explains how continents
move
Earth’s crust divided into
giant irregular shaped
plates that essentially float
on the mantle causing the
continental drift
Plates moving away
from each other
Plates sliding past
each other/
earthquakes
Plates colliding/
mountain ranges
San Andreas
Fault in
California/810
miles
Pacific plate
and North
American plate
Continental Drift
Reshaping of the physical environment and
climate
Altering the habitats in which organisms live
Species extinction and new opportunities
Explain why similar animal and plant fossils are
found on different continents
Evidence of Evolution
Ø Morphological divergence
Ø Morphological convergence
Ø Comparative embryology
Ø Molecular biology
Morphological Divergence
Anatomical similarities between species reflect common descent
Homologous structures (different use, similar structure) are
variations on an anatomical structure of an ancestral organism
Remodeling of structures to fit certain functions, descent with
modification
Forelimbs
Morphological Convergence
Analogous Structures
Do not infer evolution
Similar functions, different structures
Evolved independently
Comparative Embryology
All organisms of a group have similar development
Same master gene directing development