Lecture 3 Flashcards
state the 4 important elements of Darwin’s theory
- Evolution occurs primarily at the level of populations - individuals do not evolve
- Variation is not directed by the environment - individuals do not induce adaptive variation when needed
- Most fit type depends on the environment and changes from generation to generation
- ‘Survival of the fitter’ - evolution works with available variation, and will not necessarily achieve perfection
State the implications of Darwin’s theory
The concept of a changing universe; a phenomenon with no purpose
State the 4 sources of evidence for evolution:
- Geology
- Homology
- Biogeography
- Domestication
Lessons from Geology
- Earth is very old - this allows for an immense amount of time for biological evolution
- Intermediate forms - evidence for transitional fossils linking features of seemingly dissimilar relatives (eg ungulates and whales, or tetrapods and fish)
- Fossils in younger strata increasingly resemble modern species in the same region - older strata show increasing differences
Give an example of how discoveries of transitional fossils continue today
Tiktaalik roseae, discovered 2006
- has 2 legs and 2 fins
- nickname: fishapod
Define homology
Similarity of traits in two or more species that is due to inheritance from a common ancestor
Lessons from homology
Vestigial traits provide evidence of the evolutionary past:
- have no function/reduced function in extant organisms
- can only be explained by the presence of functional traits in ancestors, followed by evolutionary degredation
Homologous structures are ubiquitous across organisms:
- fundamental structural similarity reflects common ancestry
- homologous structures have evolved to serve very different functions
Define a vestigial structure
- features inherited from an ancestor, but reduced in morphology and function
- are homologous to functional structures in related species
Describe vestigial structures in Galapagos flightless cormorants compared to mainland cormorants
Mainland cormorants need to fly as they nest on trees; GF cormorants do not as they nest on rocks by the water. The wings of these two species, albeit varying in use, are homologous structures.
what is a vestigial structure in cave-dwelling morphs of Astynax Mexicanus?
they have evolved to lose their eyes as they do not need them
vestigial structures in humans
- ear muscles
- appendix
- tailbone
- goosebumps
why is the presence of vestigial structures significant?
- organismal features are consistent with modifications of pre-existing structures
- this would not be expected if each organism was individually optimally designed
describe homology in genes
- approximately 500 genes are shared across all forms of life
- there is a strong, shared constraint for genes involved in basic cellular function (eg transcription/translation)
Lessons from Biogeography
Remote islands biotas:
- have continental affinities
- 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
3 main points of 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
