FORMATION OF NEW SPECIES
• Speciation- when over
time, 2 populations
become so different
that they can no longer
interbreed.
There are 3 steps to
speciation
1. Separation
2. Adaptation
3. Division
1. Separation- portion of the
population becomes
isolated.
Example: canyon forms, mountain
range, volcano, tsunami
For example, a population of wild fruit flies
minding its own business on several bunches
of rotting bananas, cheerfully laying their
eggs in the mushy fruit…
Disaster strikes: A hurricane washes some of the
bananas and the immature fruit flies they contain out to
sea. The banana bunch eventually washes up on an island
off the coast of the mainland. The fruit flies mature and
emerge from their slimy nursery onto the lonely island.
The two portions of the population, mainland and island,
are now too far apart to reproduce with each other. At
this point, speciation has not occurred—any fruit flies that
got back to the mainland could mate and produce healthy
offspring with the mainland flies.
2. Adaptation-as the
environment changes, so
may the population living
there change and evolve
separately to form separate
species.
The populations diverge: Ecological conditions
are slightly different on the island, and the island
population evolves under different conditions and
experiences different random events than the
mainland population does. Color, shape, food
preferences, and courtship displays change over
the course of any generations of natural
selection.
3. Division– over hundreds to
thousands of generations, the 2
groups became so different that
they were no longer the same
species and could no longer
interbreed.
So we meet again: When another storm reintroduces
the island flies to the mainland, they will not readily
mate with the mainland flies since they’ve evolved
different courtship behaviors. The few that do mate with
the mainland flies, produce inviable eggs because of
other genetic differences between the two populations.
The lineage has split now that genes cannot flow
between the populations.
The Kaibab squirrel (right) became isolated in
the Grand Canyon ~ 10,000 years ago. Features
have gradually evolved that separate it from
close relative, the Abert squirrel (left) .
Croatian
Lizards
• Experiment: Scientists removed
5 pairs of insectivorous species to
a new island habitat
• Old island habitat had very little
plants – Lizard diet was 93%
insects, 7% plants
• New island habitat had an
abundance of plants
• After 40 years, the lizard diet was
36% insect and 64% plant
• In just a few decades the lizards
have developed a completely new
digestive structure, larger
heads, and a harder bite,
researchers say.
Galapagos tortoise
• All subspecies of Galapagos
tortoise evolved from a common
ancestor that arrived from mainland
South America about 6-12 million
years ago.
• A volcano formed the oldest
Galapagos Island. Tortoises that
arrived there colonized the island.
• The distance between the islands
prohibited much inter-breeding and
resulted in independent evolution of
the populations.
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tch?v=yVqJ_mQazik
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