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• What are Darwin's finches?
• When Darwin fist came to the Galapagos
islands back in the 1800’s he noted that
there existed a variety of finches that all
seemed to be derived from a common
• He had no way to test this hypothesis at
the time but conjectured that a common
finch flock may have been blown several
hundred miles off coarse from the South
American Mainland
• This flock would then have subsequently
populated and diversified on the
Galapagos Islands
• This process of modification over time to
fill a variety of niches is adaptive radiation
Put another way…
• It is “the emergence of numerous species
from a common ancestor introduced into a
new environment, presenting a diversity of
new opportunities and problems”
– Campbell, Biology
• This happens in instances when there
exist unrealized opportunities in a new
• Over time once rare characteristics are
emphasized and beneficial. This s
divergent or directional selection
depending on the circumstance
Divergent evolution
• Traits with similar internal structure are
called homologous traits
• When homologous features become used
for different purposes - are no longer
analogous - the process is called
divergent evolution, the splitting of a
family tree in different directions.
Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College.
Convergent evolution
• When unrelated groups have analogous
but nonhomologous features (wings in
birds and butterflies, fins in squids and
seals), the process is called convergent
evolution (sometimes parallel evolution)
- similar needs produce similar structures,
even if they're based on different
architecture. Both support the concepts
of evolutionary change by selection.
• Due to similar selection pressures that are
consistent over long periods of time,
unrelated organisms (or distantly related
ones) acquire similar traits to deal with
those similar pressures.
Convergent evolution
Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College.
The following is taken from…
(and adapted by Mr.R)
• Peter and Rosemary Grant, spent part of
each year since 1973 in a tent on a tiny,
barren volcanic island in the Galapagos.
• They caught, weighed, measured, and
identified hundreds of small birds and
record their diets ever year.
• “In their natural laboratory, the 100-acre island
called Daphne Major, the Grants and their
assistants watched the struggle for survival
among individuals in two species of small birds
called Darwin's finches.”
• “The struggle is mainly about food -different types of seeds -- and the
availability of that food is dramatically
influenced by year-to-year weather
“For the finches, body size and the size
and shape of their beaks are traits that
vary in adapting to environmental niches or
changes in those niches. Body and beak
variation occurs randomly.”
• “The birds with the best-suited bodies and
beaks for the particular environment
survive and pass along the successful
adaptation from one generation to another
through natural selection.”
What the Grants Witnessed
“Natural selection at its most powerful
winnowed certain finches harshly during a
severe drought in 1977. That year, the
vegetation withered. Seeds of all kinds were
scarce. The small, soft ones were quickly
exhausted by the birds, leaving mainly large,
tough seeds that the finches normally ignore.
Under these drastically changing conditions, the
struggle to survive favored the larger birds with
deep, strong beaks for opening the hard
“Smaller finches with less-powerful
beaks perished.”
“The big-beaked finches just
happened to be the ones favored by
the particular set of conditions
Nature imposed that year.”
Life is
• “The Grants found that the offspring of the
birds that survived the 1977 drought
tended to be larger, with bigger beaks. So
the adaptation to a changed environment
led to a larger-beaked finch population in
the following generation.”
“Adaptation can go either way, of course.
As the Grants later found, unusually rainy
weather in 1984-85 resulted in more small,
soft seeds on the menu and fewer of the
large, tough ones.”
“Sure enough, the birds best adapted to
eat those seeds because of their smaller
beaks were the ones that survived and
produced the most offspring.”
Long Live
Examples of Adaptive Radiation