Download natural selection 2

Darwin’s voyage aboard HMS Beagle.
• 1831-1836 trip around the world..
• Collected countless specimens and kept detailed notes.
Returning home, Darwin married and
moved to a country home.
For the next 20 years, he published
books about his findings on the Beagle
and worked quietly on the “species
problem”.
Finches of
the
Galapagos
Islands
Darwin knew about artificial selection, which is the intentional
selection of certain traits (i.e. purebred dogs). He figured that the
same types of processes must happen in nature.
Wild mustard
& domestic
cruciform
vegetables
Domestic dogs
Wild canids
This led him to the idea of natural selection.
Natural selection is “the survival of the fittest.”
What do you think that means?
Organisms that are better suited to their environment will
survive and reproduce.
Natural selection rests on three indisputable facts:
1. Organisms produce more offspring than can survive.
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2. Individuals vary in their characteristics.
Which mice would be better suited to a dark
environment?
Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings
3. Many characteristics are inherited by offspring
from their parents.
If a black mouse and a white mouse breed…
Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings
It follows logically that …
• Some individuals will be better suited to their
environment - they will survive and reproduce
more successfully than individuals without those
characteristics.
• Future generations will thus contain more genes
from better-suited individuals.
• As a result, characteristics will evolve over time
to resemble those of the better-suited ancestors.
Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings
What gets natural selection started?
Occasionally, members of a population acquire a genetic
mutation that changes the organism’s phenotype.
Sometimes the mutation is bad…
Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings
But sometimes the mutation is advantageous….
Some bacteria acquire a genetic mutation that makes them
resistant to antibiotics. Some antibiotics cannot kill these
bacteria, so they live and reproduce.
Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings
If the mutation is advantageous then the
organisms with the mutation will survive and
reproduce more.
The organisms without the mutation will die
faster, and eventually more of the organisms
with the mutation will be left.
Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings
These mutations are not a choice of the
organism, but rather a random genetic
event.
Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings
Favorable traits that result from mutations
are known as adaptations.
Fitness is the likelihood that
an individual will reproduce
and/or the number of
offspring an individual
produces over its lifetime.
Adaptive trait or adaptation
is a trait that increases an
individual’s fitness.
Phylogeny of the Galapagos Finches
The development of pesticide resistance in insects is another
example of real-time evolutionary change.
Natural selection is also
responsible for:
• antibiotic resistance in
bacteria
• herbicide resistance of
weeds
• HIV resistance to antiretroviral drugs