Darwin Finches modified

Darwin’s Finches and
Natural Selection
Cheryl Heinz, Dept. of Biological Sciences, Benedictine
University, and Eric Ribbens, Dept. of Biological Sciences,
Western Illinois University
The Galapagos Islands
• Located approximately
1000km from the coast of
Ecuador, South America.
• This is just a little closer
than the distance
between Chicago and
– Mostly ground between the
two U.S. cities.
– Mostly deep water between
the Galapagos Islands and
the coast of South America.
• Terrestrial species on these islands won’t have many
relatives nearby.
• Neighboring islands will have close relatives
– but new terrestrial species won’t arrive on these islands from
the South American mainland very often.
– most of the island species have had plenty of time to
differentiate from their nearest living relatives.
• Another way of saying this is that there is very little
gene flow between the islands and the mainland.
– Gene flow = animals of the same species but a different
gene pool are introduced into a population
CQ1: Limited gene flow means:
A: Birds rarely move between the
mainland and the islands.
B: Birds on the island have the same
genes as birds on the mainland.
C: Birds on the mainland don’t like birds
from the islands.
D: Birds on the mainland won’t evolve, but
birds on the islands might.
Charles Darwin
• Darwin explored these islands from April through
October 1835.
– Entire voyage of The Beagle: Dec 1831 - Oct 1836
• When and where he started thinking about what
was to become his theory of evolution by natural
• He did not publish his thoughts until the
publication of The Origin of Species in 1859.
Charles Darwin’s Ideas
• Biological evolution is change in
species over time.
– This was not a new idea at the
– But there were no good
mechanisms to explain how these
changes occurred
• Natural selection is just such a
mechanism, and this is what
Darwin contributed.
Galapagos Endemics
• The Galapagos today is an amazing place.
• Animals live there that are found nowhere
else on earth.
– This makes them endemic
– Perhaps the most famous of the endemic birds are
the finches, of which there are 13 different species
• The islands are a natural laboratory, and one
in which evolution can be observed.
Among the kinds of animals
found here and nowhere else:
– 1 penguin species
– 1 giant tortoise species
– 1 marine iguana species
– 7 species of lava lizard
– 14 species of sea cucumber
– 1 species of sea lion
– 1 species of hawk
– several species each of
mockingbirds, doves, owls,
flycatchers, and yellow
The Finches
• The 13 finch species include:
6 species of ground finches
3 species of tree finches
1 woodpecker finch
1 vegetarian finch
1 mangrove finch
1 Coco Island finch
• A warbler finch that looks more like a warbler
than a finch (one of the tree finches).
• The woodpecker finch actually uses cactus
spines to dig grubs out of branches!
Evolution is:
A change in the frequency of an allele, such as an
allele for beak depth, is the basic definition of
Evolution by Natural Selection
1. Individuals vary in some traits.
2. Some of the differences in traits are
passed along to offspring.
– This requires a genetic basis to the trait
– The trait is thus heritable
Evolution by Natural Selection
3. Different individuals produce different
numbers of surviving offspring.
– Produce different numbers, or
– Different numbers survive.
4. The particular value of a trait is
connected to the number of offspring
– Traits that allow for more offspring to be
produced are said to be “naturally selected.”
Types of evolution
• Microevolution – changes in the gene
(allele) frequencies in a population over
a short period of time
• Macroevolution – changes in the gene
(allele) frequencies in a population over
a large amount of time that essentially
differentiates a population from the rest
of the species.
• Changes in the population are due to 4
main mechanisms:
– Mutation
– Natural selection
– Gene flow
– Genetic drift