The Evidence for Evolution
The many forms of evidence that convinced
Darwin of the evolution of species and enabled
him to formulate his theory.
Biogeography
• The observed geographic patterns of distribution of
species
Biogeography
• Closely related but different
• The birds have a
common ancestor on
the mainland, but
after becoming
geographically
isolated on islands
developed
adaptations to suit
the differing
environments of the
islands.
Biogeography
• Distantly related but similar
• Distantly related rodents, that live in
similar environments have developed
similar body types
Darwin’s Hypotheses
He realized the patterns he had observed
regarding the distribution of species, both
living and extinct, were evidence that species
might have evolved.
He hypothesized that remote oceanic islands
became populated by species that arrived by
water or air.
After the species became established, many
evolved into new species over time.
Darwin’s Hypotheses
Observations from the Galapagos
Islands
Darwin’s hypotheses regarding
remote islands
Only these kinds of organisms are
Many species of birds, plants,
able to reach remote islands by
insects and in some cases, reptiles
crossing open ocean
Amphibians and most mammals
No native amphibians and very few
cannot cross open ocean and won’t
land mammals
be found on remote islands
Over time, ancestral species have
Many unique species found
evolved into new geographically
nowhere else of Earth
isolated species
Unique species are descendents of
Unique species most closely
ancestral species from the nearest
resemble species on the nearest
land masses and will have some
continental land mass
similarities
Testing Darwin’s Hypotheses
• To date, Darwin’s hypotheses have been
supported by the observations of life on all
remote islands.
• For example, looking at Hawaii:
– No native amphibians or mammals (exception of
bat and sea lion)
– Unique plants, birds and insects
– No native terrestrial reptiles
Testing Darwin’s Hypotheses
• With your table partner or groups of 3, read
the textbook handouts provided.
– Sections: Homologous and Analogous Features,
Vestigial Features and Anatomical Oddities and
Competition within Populations
– Each student make a summary of one of the
sections and share it with their group mates.
– Answer the questions in section 7.4 #’s 1-8
In his book, Darwin made two main points.
• All species of organisms living on Earth today
are descended from ancestral species. In other
words, species evolve over time.
• The mechanism that causes species to change
over time is natural selection.
Next day: The Origin of Species