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Theories of Evolution

Inheritance of acquired characteristics

• Proposed by Jean-Baptiste Lamarck

• Theory

▫ Each individual can change their own traits through use/disuse

▫ Evolution occurs to an individual within a lifetime

Inheritance of acquired characteristics

• These new traits would be passed to offspring

• Example:

▫ Giraffes stretch out their necks due to scarcity of food and passed that trait onto their offspring

• Not widely accepted

Natural Selection

• Proposed by Charles Darwin

• Theory

▫ The fittest organism (as determined by the environment), in a population will survive to reproduce and pass on their traits to their offspring

• Evolution occurs in a population over many generations

Lamarck/Darwin Comparison

Natural Selection

• Example 1:

▫ Peppered moth – lighter peppered moths in England blended in with trees covered with lichen (selection against darker variation).

More light moths, less dark moths

▫ Industrial Revolution Trees covered with soot, darker moths were able to blend in and more survived to pass on their traits (selection against lighter variations)

More dark moths, less light moths

Natural Selection

• Example 2: Antibiotic resistance

▫ Certain bacterial cells are more resistant to antibiotics than others

▫ Over time, cells can pass the resistance to offspring resulting in bacteria that are highly resistant to antibiotics (aka superbugs)

Evidences for evolution

1) Fossil evidence

▫ Fossil – mineralized remain of an organism – can be found between layers of sedimentary rocks

▫ Can look at the overall picture of how a species has evolved based on its environment (Horse leg bone and teeth structure)

▫ Older fossils are deeper (relative dating)

Evidences for evolution

2) Shared Anatomical Structures

a) Homologous

2 organisms have SAME bone structure with DIFFERENT functions

Shows common ancestor (or origin)

Shard Anatomical Structures

▫ Example

Bird wing and human arm

Evidences for evolution

b) Analogous

2 organisms have similar structure and SAME function

No common ancestor

Shared Anatomical Structures

▫ Example:

Shark and dolphin fins

Bird and butterfly wings

Evidences for evolution

c) Vestigial

▫ Body part that no longer has a purpose

▫ Examples:

Eyes on a blind fish

Leg bones on a whale

Human appendix

Wisdom teeth

Human tailbone (coccyx)

Wings on flightless birds

Shared Anatomical Structures

Evidences for evolution

3) Biochemical (molecular) similarities

▫ Sequence matters – more similarities in DNA and amino acid sequences indicates common ancestry

▫ Example:

Similarities in human, gorilla, chimpanzee hemoglobin

Evidences for Evolution

4) Embryology

▫ Various organisms have very similar early embryological structures