Download Chapter 10 Notes, Part II

Chapter 10 Notes, Part II
The Theory of Natural Selection
Publication of On the Origin of Species
• In 1858, Darwin
received an essay from
Alfred Russel Wallace, a
naturalist working in
Malaysia. Wallace’s
thoughts on evolution
were very similar to
Darwin’s. This finally
got Darwin to publish
his theory, after almost
25 years.
Publication of On the Origin of Species
• In 1859, On the Origin of
Species by Means of
Natural Selection was
published.
• In this book, his theory of
evolution, called natural
selection, was explained.
• It caused a sensation;
some were appalled and
some thought it to be
brilliant.
Publication of On the Origin of Species
Inherited Variation
• One of Darwin’s most
important insights is
that members of any
species have variations,
or differences, among
each other.
• He had no idea of how
heredity, or genes,
worked.
• He argued that variation
was important. This
was revolutionary, b/c
in his day, variations
were thought to be
imperfections.
• He observed and
reasoned that some
variations were
inherited.
Inherited Variation
• Darwin noted that
farmers (both plant and
animal) used this
hereditable variation to
improve their breeds.
• Ex: some hogs are
“meatier” than others,
some horses are faster
than others, some cows
give more milk, some
sheep have better wool
Inherited Variation/ Artificial Selection
• These farmers, or
breeders, only selected
the most favorable
traits to breed. Over
many generations, the
species would be
different than the
original population.
• Population is defined as
all the individuals of a
species living in a
particular area.
• Nature provides the
variation, but since it is
humans SELECTING
which traits are
favorable/useful (not
nature), this is called
artificial selection.
Artificial Selection
Artificial Selection
Artificial Selection
Evolution by Natural Selection
• Natural selection
is also called
“survival of the
fittest.”
• This theory is an
explanation for
how life changes
over time, or
evolves.
• 5 main parts of
this theory.
Evolution by Natural Selection
I.
In nature, organisms
produce more offspring
than can survive. This sets
up a struggle for existence.
Ex. A female cod can produce
4-6 million eggs in one
spawning; a female mouse
can have 48 babies each
year; a fly lays
about 250 eggs at a time
Evolution by Natural Selection
II. In any population,
variation exists
among
individuals.
Ex. Human skin
color, speed of
gazelle, size of a
deer’s antlers
Evolution by Natural Selection
III. Some variations give an
individual an advantage in
surviving and reproducing
in their environment
•
These variations are called
adaptations.
•
Can be physical or
behavioral
•
Fitness is a measure of an
organism’s ability to
survive and reproduce in
its specific environment.
Evolution by Natural Selection
IV. The offspring of these
individuals, if the
adaptation is
hereditable, are likely to
have the adaptation,
too. They will likely live
longer and produce
more offspring b/c they
also have the
adaptation.
Evolution by Natural Selection
V. Over time, offspring
with certain
adaptations make up
most of the population
and may look entirely
different from their
ancestors.
• Darwin reasoned that
each living species has
descended, with
changes, from other
species over time. This
is referred to as descent
with modification.
• Implies all living things
are related to one
another through
common descent.
Example of Natural Selection Today
Antibiotic-resistant bacteria
• Natural populations of bacteria contain
considerable variation, primarily as the result of
mutations. When exposed to antibiotics, most
bacteria die quickly, but some may have
mutations that make them slightly less
susceptible.
• These surviving bacteria will then reproduce
again, producing the next generation. This
population contains more bacteria that have
some resistance against the antibiotic.
Example of Natural
• At the same time, new mutations occur,
contributing new genetic variation to the existing
genetic variation. Spontaneous mutations are
very rare, and advantageous mutations are even
rarer. However, populations of bacteria are large
enough that a few individuals will have beneficial
mutations. If a new mutation reduces their
susceptibility to an antibiotic, these individuals
are more likely to survive when next confronted
with that antibiotic. Given enough time, and
repeated exposure to the antibiotic, a population
of antibiotic-resistant bacteria will emerge.
Evidence of Evolution
The Fossil Record
• Darwin saw
fossils as a
detailed record
of the history of
life on Earth.
Evidence of Evolution
Homologous Body
Structures
• There are striking
similarities in the body
parts of different
species.
• Ex: Consider the limbs
of a human, cat,
whale, and a bat .
Though they look
different and function
differently, they all are
formed by the same
bones.
Evidence of Evolution
• Each of these limbs has
adapted in ways that
enable the animal to
survive in different
environments.
• A body part with the
same basic structure and
embryonic origin as that
of another organism,
though not necessarily
sharing the same
function, is a homologous
structure.
Evidence of Evolution
• Not all homologous
structures serve
important functions
(caution! Next slide… )
• Some organs that don’t
function are so reduced
in size that they are just
traces of homologous
organs in other species.
• Such organs are called
vestigial organs.
Evidence of Evolution
Vestigial Structures
As far as science “knows,” they
serve no important
function. But, be
careful…scientific
knowledge grows everyday.
An organ thought to be
vestigial may be found to
have function.
Example: human appendix
Vestigial Structures
• Go to
http://www.livescience.com
/animals/top10_vestigial_or
gans.html
Evidence of Evolution
Similarities in Embryology
• The embryos of many
vertebrates, for example,
are very similar.
• The same groups of
embryonic cells develop
in the same order and in
similar patterns to
produce the tissues and
organs in all vertebrates.
• What does this imply?
Evidence for Evolution
• These are just a few of
the lines of evidence for
evolution. Others
include geographic
distribution,
distribution in time,
evidence by example,
comparative
biochemistry, etc…