Download 16-3 Evolution as Genetic Change

Chapter 16: Evolution of Populations (16-3)
How do changes lead to speciation?
 As new species evolve, populations become
rapidly isolated from each other.
 When the members of two populations cannot
interbreed and produce fertile offspring,
reproductive isolation has occurred.
o
—capable of
interbreeding, but have differences in
courtship rituals, or other behaviors. (different
songs to attract mates)
o
—separated by
mountains, rivers, oceans, etc. Genetic
changes that appeared in one group are not
passed to the other.
o
—two or more species
reproduce at different times.
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Darwin proposed that N.S. shaped the beaks of
different bird populations as they adapted to eat
different foods.
Peter and Rosemary Grant studied the medium
ground finch on Daphne Island
Chapter 16: Evolution of Populations (16-3)
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During the dry season, food became scarce…birds
became feeding specialists. The ones with the
largest beaks survived.
Beak size also plays a role in mating behavior—bigbeaks like other big-beaks, etc.
What kind of selection???
 Speciation in the Galapagos finches occurred in
six steps:
1. Founders arrive—few finches from the S. America
came to the islands.
2. Separation of Populations—finches moved to
different islands…essentially isolated from each
other and no longer shared a common gene pool.
3. Changes in the Gene Pool—Over time, populations
on each island became adapted to their local
environments. N.S. would have formed a separate
population
4. Reproductive isolation—finches choose their mates
carefully…differences in beaks and mating behavior
lead to reproductive isolation.
5. Ecological competition—species evolve in a way
that increases the differences in each bird population.
6. Continued evolution—after many generations 13
species of finch have evolved.