Download Natural selection - Peekskill City School District

Evolution and
Natural
Selection
Peekskill High School
Biology
by: First-name Last-name
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Charles Darwin
 Darwin
explored these islands from April
through October 1835.
 Entire
 When
voyage of The Beagle: Dec 1831 - Oct 1836
and where he started thinking about
what was to become his theory of evolution
by natural selection.
 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
time
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.
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Natural Selection


In any population of
organisms there is
natural variation.
Some of these
variations will allow
the organisms
possessing them to
survive and
reproduce better
than those without
these particular
traits.
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
Philadelphia.


Mostly ground between the
two U.S. cities.
Mostly deep water
between the Galapagos
Islands and the coast of
South America.
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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.
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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!
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Seeds
A
variety of seeds are produced on the
island.
 Finches
prefer the softest seeds, which are the
easiest to open.
 The
seeds above are seeds of a plant called
Caltrop, in the genus Tribulus.
 These
are among the hardest to eat.
 It takes a medium ground finch with a beak at
least 11mm long to open one.
 Ground finches with beaks that are 10.5mm long
or less haven’t even been seen trying to eat
them.
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Heritability
 It’s
important to note that beak size and
shape is heritable in these finches.
A
bird with a large, deep beak will have offspring
with large and deep beaks.
 Natural
selection can occur without
heritability, but evolution by natural selection
cannot!
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Evolution by Natural Selection
Steps:
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
(more…)
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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 produced.

Traits that allow for more offspring to be produced are
said to be “naturally selected.”
Natural Selection – Competition
 If
there are not enough resources for all of
the individuals, there will be competition
for those resources.

Survivors represent a small part of the
individuals produced each generation.
Natural Selection – Populations
Show Variation
 Which
individuals will survive is often not a
matter of luck.
 Populations show variation – individuals
are not identical.

They differ in many different traits.
Natural Selection – Variation is
Heritable
 Some
of the variation between individuals
in the population is heritable.

It can be passed down from one
generation to the next.
Upsetting Genetic Equilibrium
 Natural
selection is not the only way that
allele frequencies can change from one
generation to the next.




Genetic Drift – a random loss of alleles.
Mutation – a new mutation can add alleles.
Nonrandom mating – inbreeding increases
the number of homozygous traits.
Migration – shuffles alleles between
populations; can prevent speciation.
Summary
Resources
Upper Saddle River, N.J. Biology:
Pearson/Prentice Hall, ©2008.
https://www.google.com