Download Darwin`s Theory of Evolution

Charles Darwin’s Theory of
Evolution
Introduction
• Charles Darwin was a biologist who lived
during the 1800s
– Scientific thinking was shifting (biology & geology)
• Evolution = the process of change over time
• Darwin developed a theory that explains how
modern organisms evolved over long periods
of time through descent from common
ancestors.
Darwin’s Observations
• Darwin was invited to sail aboard the HMS
Beagle’s 5-year journey
– The captain and crew were mapping the coastline
of South America
– Darwin was collecting animal and plant specimens
and making notes about the biological diversity
(species) he observed
– They visited South America, remote islands, New
Zealand, Australia, and the southern tip of Africa
Examples
• Birds:
– Rheas are similar to ostriches but live on separate
continents
– Finches on the Galapagos Islands were similar but
each species had a differently-shaped beak
• Marsupials are found only on Australia
• Fossils
– Many fossils that Darwin collected resembled
living species.
Other Scientists’ Ideas
• James Hutton and Charles Lyell (Geologists)
– Concluded that the Earth is extremely old
– The processes that changed Earth in the past were
still operating in the present.
• Jean-Baptiste Lamarck (Biologist)
– Suggested that organisms could change by using
or not using parts of their bodies
• Thomas Malthus (Economist)
– Studied factors that limited population growth
Artificial Selection
• Plants and animals are bred for certain
characteristics
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Cows that produce more milk
Horses that run faster
Plants that produce better fruit
Dogs that possess certain skills (dog breeds)
• Artificial selection = nature provides the
variations in a species, but humans select those
that they find useful.
(Darwin had NO idea how heredity worked)
Darwin’s Conclusions
• Organisms struggle to survive
– They compete for limited resources
• Some variations are more beneficial than
others (adaptations)
– Individuals with these variations were more likely
to reproduce and pass them on to offspring.
• “Survival of the fittest”
– An organism’s fitness describes how well it is able
to survive and reproduce in its environment
Natural Selection
• The process by which organisms with certain
variations are more likely to survive and
produce more offspring.
– The natural environment determines fitness
• Natural selection exists when organisms
compete for resources, possess variations, and
there are different levels of fitness among
individuals in a population.
Evidence for Evolution
1. Biogeography – Patterns of species distribution
– Closely related but different = variations among populations that
resulted in the development of different species
– Distantly related but similar = species that are similar and live in
similar environments but in different locations
2. Fossils
– The geologic record of organisms that have lived in
the past
– Some extinct organisms are similar to living species.
3. Anatomy and Embryology
– Homologous structures = structures that are
anatomically similar but have different uses
• Ex: arm bones of amphibians, reptiles, bird wings, and
mammals
– Vestigial structures = traces of structures
• Ex: hip bones in marine mammals, tailbones
– Embryos of different species show similar
development patterns
4. Genetics and Molecular Biology
– All organisms share the same basic genetic code