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 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 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?

• Embryology: the study of the embryonic stages of organisms.

Evidence: The embryological similarities among organisms (embryology).

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)

http://www.pbs.org/wgbh/evolution/library/03/4/l_034_04.html

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.

Want to find out more????

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?