I can explain how the
• The fossil record
• anatomical and embryological similarities,
• and molecular (DNA) similarities and
• direct observation
can be used as evidence for the evolutionary development
of a given species
The fossil record
Remember when we looked at the
fossils?
• Fossils provide evidence of past life
Remember twine time?
• species found early in the history of
life were simple single-celled organisms
and became more and more complex over time.
Transitional species found in fossil record
fish –amphibian (Tiktaalik fossil)
Vestigial legs in dolphins found
Transitional
fossils:
bird/reptile
Archaeopteryx
J-park scene:
comparing dinosaur
fossils to modern day
birds
Evidence: structural similarities
(a.k.a. homologies/homologous structures)
1. Homologies
• Evolutionary theory predicts that related organisms will share
similarities that are derived from common ancestors.
• Similar characteristics due to relatedness are known as
homologies.
• Homologies can be revealed by comparing the anatomical
structures of different living things, studying embryological
development in different organisms, cellular similarities and
molecular (especially DNA) similarities between organisms.
Spines, flowers, insect –catching traps and pits
are all modified ______________________?
What function do the modified leaves serve for each of the 4 types of plants?
Another example of homology is the forelimb of tetra pods (vertebrates with legs).
Humans, cats, whales and bats all have different forelimbs, reflecting their
different lifestyles. But those different forelimbs all share the same bone elements
- the humorous, the radius, ulna and other bone elements in common.
• Some of the most interesting homologous structures are
vestigial structures, structures of little, if any importance
to current organisms. Vestigial structures are organs or
structures remaining or surviving in a degenerate, or
imperfect condition or form.
Vestigial pelvis and legs
• Snakes have legged ancestors.
Some species of living snakes have hind limb-buds as early
embryos but rapidly lose the buds and develop into legless
adults. The study of developmental stages of snakes, combined
with fossil evidence of snakes with hind limbs, supports the
hypothesis that snakes evolved from a limbed ancestor.
Photo to the left, the Cretaceous
snake Pachyrhachis
problematicus clearly had small
hindlimbs. The drawing at right
shows a reconstruction of the pelvis
and hindlimb of Pachyrhachis.
What are some other examples of vestigial
structures?
• Figure 2.1.1. Vestigial structures of various organisms. From top to
bottom: A. A hypocritical ostrich with its wings extended. B. A blind
cave salamander - look closely for the eyes buried underneath the
skin. C. Astyanax mexicanus, the Mexican tetra, a blind cave fish.
Back to question 2
Vestigial legs in dolphins found
Vestigial structures in humans?:
• Wisdom teeth
• Appendix
• Coccyx- (tail bone)
Evidence: embryological similarities
Embryological similarities
• Darwin saw that embryonic resemblances would be a very
strong argument in favor of the genetic connectedness of
different animal groups.
•What
species is
this????
Ultimately: the body form of an organism is controlled by its
DNA (genes) – stay tuned 
(Hox genes)
Homologies: at the cellular level
• All living things are fundamentally alike.
• At the cellular level living things are remarkably similar
to each other. These fundamental similarities are most
easily explained by evolutionary theory: life shares a
common ancestor.
What cellular structures are shared by all eukaryotic
organisms?
Evidence: The molecular similarities among organisms
• What genetic code is shared by all species?
DNA!!
The molecular level (cont)
In fact, the DNA code itself is a homology that links all life on Earth
to a common ancestor. DNA and RNA possess a simple four-base
code that provides the recipe for all living things. In some cases,
if we were to transfer genetic material from the cell of one living
thing to the cell of another, the recipient would follow the new
instructions as if they were its own.
• These characteristics of life demonstrate the fundamental
sameness of all living things on Earth and serve as the basis of
today's efforts at genetic engineering.
The genetic similarities among organisms
Back to index
GFP traditionally refers to the
protein first isolated from a
gene found in the jellyfish
Aequorea victoria which glows
in the dark.
• The GFP gene can be transferred to other organisms
which will express this same trait.
GloFish, the first genetically modified animal to be sold as a pet
Genomic comparison evidence
• Comparative genomics is a field of biological research in which
the genome sequences of different species — human, mouse,
and a wide variety of other organisms from bacteria to
chimpanzees — are compared. By comparing the sequences of
genomes of different organisms, researchers can understand
what, at the molecular level, distinguishes different life forms
from each other. Comparative genomics also provides a
powerful tool for studying evolutionary changes among
organisms, helping to identify genes that are conserved or
common among species, as well as genes that give each
organism its unique characteristics.
• genomic comparisons article
• Protein comparison
Evidence:the pattern of organism groupings.
• Classifying life based on evolutionary relatedness
Evidence: The direct observation of evolutionary changes in the
laboratory and in the wild.
• Darwin’s views on the role of environmental
factors in the screening of heritable variation was
heavily influenced by artificial selection.
• Humans have modified a variety of domesticated
plants and animals over many generations by
selecting individuals with the desired traits as
breeding stock.
The domestication of corn (a somewhat corny example)
http://www.hhmi.org/biointeractive/breeding-corn-teosinte
artificial selection- dogs
Want to learn more????
Here are some great sites to check out!!
• Understanding evolution (UC Berkeley) :http://evolution.berkeley.edu/
• PBS Evolution site: http://www.pbs.org/wgbh/evolution/
• The Complete Work of Charles Darwin Online: http://www.topsite.com/goto/darwin-online.org.uk
• The American Association for the Advancement of Science:
http://www.aaas.org/news/press_room/evolution/
• The National Science Foundation: http://www.nsf.gov/news/special_reports/darwin/home.jsp
• Science Daily- current findings in evolutionary biology:
http://www.sciencedaily.com/news/fossils_ruins/evolution/
• Nature: http://www.nature.com/nature/supplements/insights/evolution/
• Howard Hughes Medical Institute
http://www.hhmi.org/biointeractive/browse?field_bio_format_type%5B0%5D=23448&field_bio_bi
ointeractive_topics%5B1%5D=23477
I can
•describe the similarities and/or differences
(i.e., embryology, homology, analogous
structures, genetic sequences) of given
organisms in terms of biological evolution.
I can
• describe relationship(s) among organisms based on
similarities and/or differences in physical and/or
functional characteristics.