Evidence for Evolution P1
S&T: 3 pg. 310 Examples of types of evidence that
Darwin (and other scientists) gathered to develop
the theory of evolution:
1. Structural similarities among organisms (anatomy).
2. Geographic distribution of organisms
(biogeography).
3. The embryological similarities among organisms
(embryology).
4. The pattern of organism groupings (phylogeny).
5. The direct observation of evolutionary changes in
the laboratory and in the wild.
6. The molecular similarities among organisms- were
found after Darwin (molecular biology- more to
come).
7.Bonus line of evidence: Transitional species found in
fossil record (paleontology).
Evidence from the study of anatomy and
physiology: structural similarities
(a.k.a. homologous structures and
embryology)
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 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?
Example of a homologous
structure in plants
• Each leaf has a very different shape and function, yet
all are homologous structures, derived from a
common ancestral form. The pitcher plant and Venus'
flytrap use leaves to trap and digest insects. The bright
red leaves of the poinsettia look like flower petals. The
cactus leaves are modified into small spines which
reduce water loss and can protect the cactus from
herbivory.
Another example of homology is the forelimb of tetrapods
(vertebrates with legs).
Humans, birds, pterosaurs, bats, seals, penguins, lizards and
whales all have different forelimbs, reflecting their different
lifestyles. But those different forelimbs all share the same
bone elements - the humerus, the radius, ulna and other
bone elements in common.
Directions: color the humerous, ulna, radius, and wrist
bones and digits, make sure each bone is assigned a
different color.
• Some of the most interesting homologous structures
are vestigial structures.
• Vestigial structures are organs or structures
remaining or surviving in a degenerate, atrophied, or
imperfect condition or form.
Vestigial pelvis and legs
found on a snake!
• Snakes have legged ancestors.
Some species of living snakes have hind limbbuds 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 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.
Vestigial legs in dolphins found
Vestigial structures in humans:
•
•
•
•
•
Wisdom teeth
Appendix
Coccyx- (tail bone)
tonsils
Arrector pili (smooth muscles that contract
involuntarily to give you “goosebumps”).
Evidence from biogeography: the study
of the geographic distribution of
organisms
• Biogeography is the study of the past and present
distribution of species.
• The distribution of living things on the globe
provides information about the past histories of
both living things and the surface of the Earth. This
evidence is consistent not just with the evolution of
life, but also with the movement of continental
plates around the world-otherwise known as plate
tectonics.
• Remember Chapter 13?
Remember building bridges??
Geography- continued
• Marsupial mammals are found in
the Americas as well as Australia
and New Guinea, shown in
brown on the map at right. They
are not found swimming across
the Pacific Ocean, nor have they
been discovered wandering the
Asian mainland. There appear to
be no routes of migration
between the two populations.
How could marsupials have
gotten from their place of origin
to locations half a world away?
• The distribution of living plants and animals suggests
that organisms adapted to one environment can invade
a new environment, and develop specific adaptations
to the new conditions.
• On the HMS Beagle, Darwin noted that in South
America, temperate species tended to resemble their
South American tropical relatives, rather than
temperate species in Europe. On the Galapagos, most
species had a recognizable ancestor from the coast of
Ecuador, but species there had numerous adaptations
specific to the climate of the Islands.
• Wallace observed the same pattern in many different
parts of the world.
Tracing the evolution of fruit flies Drosophila in the Hawaiian
archipelago using DNA analysis.
All of the 500 or so endemic species are descended from a
common ancestor that reached Kauai over 5 million years ago.
What evidence do you think they used to draw this conclusion?
Evidence: The embryological similarities
among organisms (embryology).
• Embryology: the study of the embryonic
stages of organisms.
Homologies: developmental biology
• Darwin saw that embryonic resemblances would be
a very strong argument in favor of the genetic
connectedness of different animal groups.
“Community of embryonic structure reveals
community of descent,” he would conclude in On
the Origin of Species in 1859.
Comparative embryology: the vertebrate
body
• Read the handout with the above title and color
the stages of embryological development. Follow
the directions provided in the reading.
Want to find out more about embryology and
evolution?
• http://evolution.berkeley.edu/evolibrary/article/history_10
• EMBRYOS SHOW ALL ANIMALS SHARE ANCIENT GENES-GREAT
ARTICLE
• What
species is
this????
Color code the associated gill arch structure on your diagram
Ultimately: the body form of an organism is controlled by its
DNA (genes) – stay tuned 
(color code your picture to show shared Hox genes)
Want to find out more????
Neil Shubin and Sean Carroll discuss homeobox genes, a set
of genes that produce basic body parts in all animals. Click
on the link below to explore the genetic tool kit used to
determine animal body form.
http://www.pbs.org/wgbh/evolution/library/0
3/4/l_034_04.html
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?