Evidence for Evolution

• Fossil Evidence• Biogeography• Islands• Homology– Anatomical– Embryo development– Molecular homology

1. Transitional forms: Fossil evidence

• Fossils or organisms that show the intermediate states between an ancestral form and that of its descendants are referred to as transitional forms. There are numerous examples of transitional forms in the fossil record.

• Here is a picture of the archeopteryx fossil

• This showed the transition from reptile to bird.

2. Biogeography• Species tend to be more closely

related to other species from the same area than to other species with the same way of life that live in different areas.

• Some marsupial mammals superficially resemble eutherian mammals (which complete their development in the uterus) from other continents.

• The resemblance between the two gliders is an example of convergent evolution

Sugarglider

AUSTRALIA

NORTHAMERICA

Flyingsquirrel

Figure 22.17

Sugarglider

AUSTRALIA

NORTHAMERICA

Flyingsquirrel

Sugarglider

AUSTRALIA

NORTHAMERICA

Flyingsquirrel

Figure 22.17

3. Islands and archipelagos • Several well-investigated

examples of this phenomenon include the diversification of finches on the Galapagos Islands and fruit flies (Drosophila) on the Hawaiian Archipelago.

4. Homology: homologous structures

• Homologous structures:structures that are similarelements and origin (common ancestry) but have adifferent function. Ex. Bat wings and human hands• Analogous structures:Structures that perform a similar function but do not have a common evolutionary origin. Ex. Insect wings and bat wings

4. Homology: embryonic development

• For example, all vertebrate embryos have structures called pharyngeal pouches in their throat at some stage in their development.

• These embryonic structures develop into very different, but still homologous, adult structures, such as the gills of fish or the eustacian tubes in mammals.

4. Homology: Molecular homology

• Proteins• DNA, RNA

Phylogenetic Trees• The process of evolution produces

a pattern of relationships between species. As lineages evolve and split and modifications are inherited, their evolutionary paths diverge. This produces a branching pattern of evolutionary relationships.

• By studying inherited species' characteristics and other historical evidence, we can reconstruct evolutionary relationships and represent them on a "family tree," called a phylogenetic tree.

Videos from PBS• Evolving Ideas: How Do We Know Evolution Happens?

This video for high school students focuses on one of the several lines of evidence for evolution -- fossils, highlighting the evolution of whales from land-dwelling mammals to the aquatic creatures we know today.

• When watching the video answer the following questions

1. What makes whales an interesting evolutionary story?

2. Describe some of the stages in the evolutionary history of whales.

3. Describe fossil evidence that supports knowledge about whale evolution.

ANSWERS

2. What makes whales an interesting evolutionary story?Whales were land mammals that went back into water. 3. Describe some of the stages in the evolutionary history of whales.- land mammals- probably lived in shallow seas where they walked around supported by water- started swimming more- fully whale like 4. Describe fossil evidence that supports knowledge about whale evolution.Pakicetus land whale ancestorBasilosaurus, fully aquatic but still had legsmesonychids, land dwelling whale ancestorsAmbulocetus, walking whales that could swimRadhocetus, aquatic animal that could probably walk a little

• Common Past, Different Paths This time-lapse microphotography of developing embryos shows the common ancestry of all vertebrates. Footage from NOVA: "Odyssey of Life.