Evidence to Support Evolutionary Theory

A. Fossils

B. Similarity of embryos

C. Homologous and analogous structures

D. Vestigial structures

E. Similarities in macromolecules• http://www.pbs.org/wgbh/evolution/educat

ors/teachstuds/svideos.html

A) Fossils• Most of the evidence for evolution comes from

the fossil record • Fossils show how much (or how little)

organisms have changed over time • One of the problems with the fossil record is

that it contains gaps. Not all organisms fossilize well, and there will be many fossils that have been destroyed by the movements of the Earth, or simply not yet been discovered.

B) Embryos of all vertebrates are similar – indicating a common ancestor

C) Homologous Structures• Develop from similar embryonic tissue• May or may not have a similar function• Suggest a common ancestor

C) Analogous Structures• Structures in unrelated organisms that

carry out the same functions• Develop from different embryonic tissues• Do not share a recent common ancestor• Superficially similar because these

adaptations evolved in response to similar environmental needs

– Wings of insects & wings of birds

Analogous Structures:These organisms do not share a recent common ancestor, but they have similar appendages that evolved to help them survive in an aquatic environment

D) Vestigial Structures• Reduced or nonfunctional structures• Examples: appendix, wisdom teeth, human tail

bone• Interpretation: the vestigial structure was

functional in some ancestor of the modern organism

• Snakes have pelvic bones; they are known to be the descendants of four-legged reptiles

Vestigial Human Structures

E) Similarities in Macromolecules-

Proteins • MORE differences in amino acid sequences of

distantly related species• FEWER differences between species that are more

closely related

Nucleic Acids • MORE differences in DNA sequences between

distant relatives• FEWER differences between species that are more

closely related

DNA sequencesAnimal

Human

Gorilla

Chimpanzee

Orangutan

Three Different Patterns of Evolution

1) Coevolution

2) Convergent Evolution

3) Divergent Evolution

Coevolution• When two species are in close association and

evolve together. Also when a species evolves as a result of evolution in another species.

• These organisms may depend exclusively on each other & be highly specialized!

Convergent Evolution• When un-related species becomes more similar

over time.• Example: streamlined bodies and swimming

appendages on sharks (fish) & dolphins (mammals)

Divergent Evolution• When related species become more different

over time.• An example is domestic dogs and wolves• Divergent evolution is the result of:

– artificial selection– adaptive radiation – where many species evolve

from one species

Label what type of evolution is occuring

Divergent Convergent Coevolution

Convergent or Divergent??Divergent:Homologous structures point to divergent evolution from a common ancestor

Convergent:Analogous structures point to convergent evolution as a result of adapting to similar environments

Question: Convergent or Divergent Evolution? Why?

Dolphins & Penguins

Answer: Convergent Evolution

Dolphins are mammals

Penguins are birds

Both have developed flippers and streamlined bodies to swim & blubber to keep warm in water

Genetic Equilibrium

• Genetic equilibrium is a theoretical condition where the frequency of alleles (traits) within a population stays the same from generation to generation

**** Genetic equilibrium does not exist *****

Five Reasons Why Genetic Equilibrium Does Not Exist

1) Migration

2) Mutations

3) Genetic Drift

4) Non- Random Mating

5) Natural Selection

1) Migration – the movement into or out of a population- Immigration – the movement INTO a

population- Emigration – the movement OUT a

population - The genes will move also!

2) Mutations – the alteration in alleles, or genetic information- New traits will form, while harmful traits will

eventually be eliminated- Creates VARIATION

3) Genetic Drift – by chance, some individuals survive to pass on their genes to their offspring.– Has nothing to do with fitness– Pure luck– Greater effect on a small

population than on a large population.

4) Non-random mating – organisms tend to mate with others in close proximity; promotes inbreeding and leads to a change in frequencies of certain traits

5) Natural Selection – the fittest will survive; bad traits will be eliminated from the population due to natural selection

Tempo of Evolution

• Gradualism is a process of evolution in which the formation of new species occurs gradually

 • Punctuated Equilibrium is a process in which

the formation of new species occurs rapidly between periods of little or no change

• Formation of new species is called speciation