BIO120 Course Introduction and Evidence for Evolution Lecture

Evidence for Evolution:

Darwin

Discovered giant armadillos that resembled (유사한) today’s armadillos but were much larger, suggesting that it was an ancestor of today’s armadillos.
Scientists later discovered the “fishapod,” which shows the transition of animals from sea to land.
- Fishapod
  - Fish + pod is a term used to describe a group of transitional fossils that possess features of both fish and tetrapods, demonstrating critical evolutionary adaptations that supported life on land.
Evidence of evolution for the whale, common ancestors, and closest living land relative is the hippo.

1. Evidence from Geology

Lessons from Geology:

Earth is very old, which allows for an immense amount of time for biological evolution.
Intermediate forms: evidence for transitional fossils linking features of seemingly dissimilar relatives (e.g., ungulates and whales, or tetrapods and fish).
Fossils in younger strata (지층) increasingly resemble modern species in the same region.
- Older strata show increasing differences.

2. Evidence from Homology

Homology: similarity of traits in two or more species that is due to inheritance from a common ancestor.

Compare the Galapagos flightless cormorant with the mainland one. Suggests that they evolved to have vestigial structures (wings) due to their environment.
- Cormorant
  - A large dark water bird that dives underwater to catch fish
Vestigial(퇴화한) Structures: features inherited from an ancestor but reduced in morphology(형태학) and function. They are homologous(동족) to functional structures in related species. Examples in humans include the ear muscles, the appendix, and the wisdom teeth:
- Ear muscles: found a lot in mammals, but we have no use for them.
- Appendix: ancestors needed it, but now it serves no purpose, and humans can remove it and be fine.
- Goosebumps: usually occur when you're cold/scared. This is hair-raising. When an animal (ex., a wolf) is fighting another, it will raise its hair as an alert/aroused signal, or when it's cold, it will raise its hair to make itself warmer, but in humans, we still have this trait even though we don't have hair.
- Tailbone
Organismal features are consistent with modifications of pre-existing structures. Not expected if each organism was individually optimally designed.
Approximately 500 genes are shared across all forms of life.
Strong, shared constraint(제약) for genes involved in basic cellular function (transcription and translation).

Lessons from Homology:

Vestigial traits provide evidence of the evolutionary past.
- Have no function (or reduced function) in extant organisms.
- Can only be explained by the presence of functional traits in ancestors, followed by evolutionary degradation.
Homologous structures are ubiquitous(어디에나 있는) across organisms.
- Fundamental structural similarity reflects common ancestry.
- Homologous structures have evolved to serve very different functions.

3. Evidence from Biogeography

Geographically close organisms resemble each other.
Different groups of organisms adapt to similar environments in different parts of the world.
Geographically isolated regions have unusual organisms.

Galapagos Islands

Formed by volcanoes and is made up of 15 different islands with varying climates.
Darwin noticed that tortoises (거북이) on different islands evolved to have different variations (e.g., tortoises on islands with lots of cacti evolved to have longer necks than ones on islands who tend to eat shrubs near the earth).
Another example is the beak(부리) diversity between finches on different islands.

Australia

Although a continent, Australia also is an island.
Distinct flora(plants) and fauna(animals) with high endemism(고유성) and many unique adaptations.
Biological uniqueness is a result of its long history of isolation from other land masses.
Australia has endemic radiations of species that are ecologically convergent with those of other continents.
- Endemic Radiations
  - When a group of organisms evolves into many new species within one place and those species are found only there.
For example, the banksia in Australia evolved to become fertilized(수정된) by mammals.
- Mammals drink nectar, pollen sticks to mammals’ body
- If mammal rubs their body part where the pollen is sticked, that nectar get fertilized.
You can also notice the parallel evolution of marsupials (Australia) with placental mammals (other continents).
Similarities and Differences
- Geographically close organisms resemble each other.
- Different groups of organisms adapt to similar environments in different parts of the world.
- Geographically isolated regions have unusual organisms.

Lessons from Biogeography:

Remote island biotas
- Have continental affinities(친밀감).
- Are dominated by good colonists.
- Have locally-differentiated species.
Biogeographically isolated regions
- Have species adapted to niches unusual for their group.
- Harbor endemic radiations of species that are convergent with radiations elsewhere.

4. Evidence from Domestication

Vast amounts of heritable variation found within species.
This variation can be selected on, leading to dramatic changes over generations.
Artificial selection as the human-imposed analog to natural selection in the wild (grape tomatoes).

165 Years Onwards…

Abundant evidence for evolution in action (e.g., antibiotic resistance).
Strength of natural selection measured in the wild—evolutionary responses can be faster than Darwin realized.
Genomic DNA evidence for vestigial traits, homology, descent with modification—molecular evolution.
Fossil discoveries have dramatically filled out knowledge of past life, including transitional forms.

Recap

Recall: Different types of evidence.
Simple Application: Similarities & differences between evidence available to Darwin and current evidence.
Easy Synthesis: How many different lines of evidence can we make sense of only by invoking evolution? What does the number of types of evidence do to the strength of our inference?
Harder Synthesis: New evidence not available to Darwin. How does it fit? Anything inconsistent?