BIOL 108 - Theme I - Evidence for Evolution

Macroevolution

Evolutionary change above the species level

Categories of Evidence for Evolution

1. Direct Observations

2. Homologous Traits

3. Fossil Evidence

4. Biogeography

Direct Observations

Evolutionary changes documented by overwhelming amounts of biological studies, especially from studies on organisms with short life spans

Examples of Direct Observations

1. Beak Morphology of Galapagos Finches based on food availability

2. Antibiotic resistance by bacteria

3. Resistance to herbicides by weeds

Morphological Homology

Comparative Embryology - Demonstrates homologous features visible during embryonic development

• More general features appear early in multiple species, demonstrates evidence for shared ancestry

Comparative Anatomy - Demonstrates homologous features visible on individuals after birth

• Ie, homology of limbs in vertebrates

• Vestigial structures as evolutionary remnants

Molecular Homology

Homologies demonstrated by similarities in genetic make-up inherited from a common ancestor

• Degree of similarity based on when they diverged from the common ancestor

Examples of Molecular Homology

1. Hox genes that regulate body planning during embryonic development in animals

2. Similarities of DNA sequence inherited from common ancestor

Fossils

Remains of species in Earth’s history, indisputable evidence and document “in-between” stages of evolution.

Downsides of Fossil Evidence

Fossils are incomplete and biased;

1. Some species live in environments that preserve their remains well

2. Certain biological materials are easier to fossilize (bones)

Benefits of Fossils to Evolutionary Studies

1. Biology of extinct species

2. Origin and diversification of some clades (ie, which clade branched off from which)

3. Relative branching order

4. Tracking of evolution over a period of time

5. Calibration of geological time for molecular study

Biogeography

Study of the past and present geographic distribution of species

Benefits of Biogeography to Evolutionary Studies

1. Assist in reconstruction of historical paths animals traversed

2. Documents distribution of phenotypic/genotypic variations

3. Monitor interacts between extant species that may lead to evolutionary changes

Endemic Species

Biological taxa native to a specific geographic area

• Populations would experience selection pressure different from populations with greater distribution

• Overtime, they may accumulate sets of genotypic/phenotypic variation leading to speciation events