Evidence for Evolution

Macroevolution

Evolutionary change above the species level

Role of Direct Observations for collecting evidence

Evolutionary changes are documented by overwhelming amounts of biological studies

• especially effective for studies on organisms with short life spans

Homologous Traits

• Homology

• Comparative embryology

• Comparative anatomy

• Molecular homology

Homology

Character traits that evolved from a common ancestral structure

Comparative embryology

homologous features visible during embryonic development

• More general features appear early in development, acting as supporting evidence for shared ancestry

Comparative anatomy

homologous features visible on individuals after birth

• Homology of limbs in vertebrates

• Vestigial structures as evolutionary remnant of ancestors (evolution removes original function)

Molecular homology

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

• Degrees of similarity is determined by how long ago they diverged from their common ancestor

Fossils

remains of species in Earth’s history

• Fossils are indisputable evidence that ancestral species existed in Earth’s history.

• Can document “in-between” stages of evolution

Issues with Fossil Record

• Fossil record is incomplete and biased:

  • Some biological materials are easier to fossilise

  • Some species live in environments that favor preservations.

Fossil Record Contributions to Study

• Biology of extinct species

• Origin and diversification of some clades (e.g. the clade of birds branched off the clade of dinosaurs)

• Relative branching order among clades (e.g. the clade of amphibians first branched off, then the clade of amniotes, etc.)

• Tracking of evolution over a long, long time

• Calibration of geological time for molecular study

Biogeography

The study of past and present geographic distribution of species

Biogeography Contributions to Study

• Assist in reconstruction of historical paths that animals traversed (e.g. how Canada geese migrate)

• Document distribution of phenotypic and genotypic variations.

• Monitor interactions between extant species that may lead to evolutionary changes (e.g. interactions between wolves and moose on Isle Royale National Park)

Endemic Species

Biological taxa that are native to a specific geographic area, and not found in other regions (often found in remote location)

Selection Pressure in Endemic Species

• Populations of endemic species would experience selection pressure different from that experienced by populations with wider distribution

  • Over time, endemic species may accumulate sets of genotypic and phenotypic variations that lead to speciation events