INTRODUCTI ON TO EVOLUTION

SCIENTIFIC THEORIES Are explanatory models that accounts for a very large body of evidence Provides the basis for explaining observations in the natural world They are not complete or perfectly accurate They are considered tentative and open for revision and refinement as new evidence is gathered EXAMPLES: Cell theory Atomic Theory

GENETIC VARIATION Original sources of genetic variation are mutations NEUTRAL mutations: results in no selective advantage or disadvantage HARMFUL mutation: reduces the reproductive success of an individual and is selected against Harmful mutations DO NOT accumulate over time. BENEFICIAL mutation: increases the reproductive success of an individual and are favoured by natural selection Beneficial mutations accumulate over time.

ARTIFICIAL SELECTION Directed breeding in which individuals that exhibit a particular trait are chosen as parents of the next generation Used to produce new breeds or varieties of plants and animals EXAMPLE: Dogs are domesticated wolves Limited by the genetic variability within the breeding population Can reduce the overall genetic diversity of the population and thus contribute to the loss of biodiversity

EVOLUTION'S BEGINNINGS.... LAMARCK made a number of significant contributions to our understanding of evolution: All species evolve over time A species evolves in response to its environment and becomes better adapted to that environment Changes are passed on from generation to generation

FOSSILS Any ancient remains, impressions or traces of an organism or trace of its activity that have been preserved in rocks or other mineral deposits in Earth's crust Provides compelling evidence that species living in the past were different from those living in the present Show that organisms become increasingly complex over time, with the most complex organisms being found in only more recent fossil deposits

PALEONTOLOGY The scientific investigation of prehistoric life through the study of fossils

CATASTROPHISM CUVIER proposed that species did not change but were eliminated by catastrophic events, only to be replaced by newly created forms His theory accounted for the different groups of species in each layer but did not account for the more complex forms

UNIFORMITARIANISM LYELL proposed that Earth's geologic features can be explained by very slow changes occurring over very long periods of time Natural laws that influence these changes are constant and eternal, and they operated in the past with the same intensity as they do today

CHARLES DARWIN Made a 5 year exploratory voyage studying various organisms Made most of his discoveries on the Galapagos Island Published “On the Origin of Species” in 1859

DARWIN’S OBSERVATIONS Many species of plants, birds, insects and in some cases reptiles No native amphibians and very few land mammals Many unique species found nowhere else on Earth Unique species most closely resemble species on the nearest continental land mass

DARWIN’S HYPOTHESES Only these kinds of organisms are able to reach remote islands by crossing large expanses of open ocean Amphibians and most mammals are unable to cross open ocean and will not be found on remote islands Over time, ancestral species have evolved into new geographically isolated species Unique species are descendants of ancestral species from the nearest continental land masses and will exhibit some similarities

TESTING DARWIN’S HYPOTHESES Darwin’s hypotheses were tentative explanations for his observations Darwin provided evidence for his theories based on the following: HOMOLOGOUS FEATURES ANALOGOUS FEATURES VESTIGIAL FEATRUES

HOMOLOGOUS FEATURES A structure with a common evolutionary origin that may serve different functions in modern species Example: A bat wing and human arm

ANALOGOUS FEATURES A structure that performs the same function as another but is not similar in origin or anatomical structure Example: A bird wing and an insect wing

VESTIGIAL FEATURES Rudimentary and non-functioning or only marginally functioning structures that are homologous to a fully functioning structure in closely related species Example: Dogs have a “dew claw” on each front limb that serves no useful function

A THEORY IS BORN… The anatomical features of different species along with fossil records provided Darwin with the evidence that: 1.Species had changed over time 2.Species appeared to share a common ancestry Darwin also hypothesized that nature may “favour” certain individuals in a population over others