INTRODUCTION 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 time2. Species appeared to share a common ancestry

• Darwin also hypothesized that nature may “favour” certain individuals in a population over others