Darwin’s Theory Descent with Modification

Biogeography –The first is a pattern in which closely related species differentiate in slightly different climates. Finches and their beak shape on the Galapagos evolved from a common mainland ancestor – but radiated out to fill different ecological habitats on the different islands

Biogeography Tortoises on the Galapagos also evolved from a mainland species – but differentiated by island due to slightly different climates

Divergent Evolution One species (a recent common ancestor) diverges into multiple species by radiating into different environments Over time collective adaptations cause populations in different environments to diverge into separate species.

Biogeography The second is a pattern in which very distantly related species develop similarities in similar environments. –Rheas, Ostriches and Emus

Biogeography

Convergent Evolution Two organisms (or groups of organisms in the case of marsupials) evolve to be similar but not from a shared RECENT common ancestor Result of similar environmental pressures that cause similar adaptive changes on multiple/separate occasions

Fossil Record

What could Darwin conclude from fossils? 1) Different organisms evolved at different times 2) Transitional fossils lend evidence that organisms had ancestral forms and changed from those ancestral forms over time 3) Determine the rough order of evolution based on what organisms appear in the lower layers then the high layers 4) Some organisms go extinct over time

Comparative Anatomy Evolutionary theory explains the existence of homologous structures adapted to different purposes as the result of descent with modification from a common ancestor.

Comparative Anatomy Similar bone structure indicates common ancestor Different function of limbs implies different selective pressures made the differences

Analogous Structures

Homologous vs Analogous Homologous – shared common ancestor (recent) – different selective pressures Analogous – no recent shared ancestor – similar selective pressures

Vestigial Structure A homologous structure that is no longer of use – but shows a relationship to other organisms that still maintain the body structure for use.

Comparative Embryology

Comparative Biochemistry Universal triplet code Similar genes and proteins Considered the strongest evidence of common heritage Quantifiable evidence – count the # of differences in amino acids – can quantify how closely related two species are

Speciation When enough adaptive differences accumulate two groups of organisms may no longer recognize each other as potential mate or have the ability to breed and produce viable offspring.

Reproductive Isolation

Geographic Isolation A physical barrier separates two populations of a species. They continue to change over time until they are considered different enough to be two species

Sympatric Speciation No barrier – but organisms utilize different resources of the environment and can become “isolated” into different populations