Transcript Natural Selection

CHAPTER 11
IDEAS ABOUT THE ORIGINS OF LIFE
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Door Number One,…
Extraterrestrial Origin – origin outside of
Earth. Life was carried here by asteroid or
meteorite.
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Door Number Two,…
Divine Creation – the process that gave rise
to life was driven by forces that cannot be
explained by science.
Gen. 1:1
In the beginning God,…
NOTE: a belief is not the same as a scientific
hypo. Any hypothesis is subject to a test which
may prove it false. Divine creation is a belief
and not a hypo. It falls outside the realm of
science.
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Spontaneous Origin – Earth developed
itself through natural chemical and physical
processes. Molecules of nonliving matter
reacted chemically and formed simple
organic molecules. These molecules
copied themselves and became more
complex. This can be copied by scientific
methods, but cannot account for the source
of the molecules. All organisms are
composed of the same basic chemicals,…
,…Proteins, lipids, carbohydrates, and
nucleic acids,…and these are composed
of the elements C, H, O, and N.
CHAPTER 12
THE THEORY OF
EVOLUTION
(The Work of
Charles Darwin)
Theory of Evolution – four main parts.
1)Variation exists within the genes of
every species. This is caused by
random mutation.
2)In a particular environment, some
individuals are better suited for
survival and so leave more offspring.
This is called natural selection.
3)Species change over time. If they do not
change or adapt to their environment, they
will become extinct.
4)The fossil record supports the statement
that species change over time.
One early explanation of evolution,...
Lamarck made one of the first attempts
to explain evolution with his theory of
acquired characteristics, which stated
that a structure developed or disappeared because of its “use or
disuse”. E.g. a giraffe
stretched its neck getting
leaves and passed this
trait to its offspring.
Darwin’s Research aboard the HMS Beagle
-He departed England in 1831 as the
ship’s naturalist on a 5-year voyage to
study plants and animals off the coast
of South America.
-He left as a creationist, believing that
each species was a divine creation,
unchanging and existing as it was
originally created. Creationism didn’t
explain the kinds and distribution of
fossils.
-He made many observations visiting the
Galapagos Islands off the coast of South
America (now Ecuador). He noticed that
animals there resembled those from the
coastal areas of South America. For
example, the Galapagos finches with beaks
specialized for the type of food they ate.
Though each different, they closely
resembled those on the coast of S.A.
Darwin Sought an Explanation
for Evolution
Malthus in 1798 –proposed,…
-The human population increased in a
geometric progression (multiply) while
the food supply increased in an arithmetic
progression (addition).
-However, this doesn’t really occur
because of disease, war, and famine
(human environment).
Population –Individuals of the same species
that live in a defined area and breed with
each other.
-a population could go way beyond the food
supply,…
-this normally doesn’t happen because of
predators, weather, and availability of
water and shelter (environment)
Natural Selection – process by which
populations change in response to their
environment.
-Individuals that possess superior physical
or behavioral attributes are more likely to
survive than those not so well adapted.
-They are also more likely to breed and
pass on their traits.
Arctic hare
Adaptation – changing of a species that
results in being better suited for the
environment. Those best suited will
survive.
Origin of Species – book written by
Darwin that has had a strong and lasting
impact.
-Presented a body of evidence that
evolution has occurred.
-Presented a hypothesis
explaining how
evolution takes place.
Darwin’s Ideas Updated
Natural selection causes the frequency of
certain genes to vary over time (death of
those not fit to breed or those not
breeding).
-Mutations and recombination of genes
(via sexual reproduction) are sources of
new variation.
-This results in microevolution – changes
that occur among species over time (exthe selective breeding of crops-Fig 12-7)
Isolation leads to species formation.
-Two populations of the same species
become separate/isolated from each other
(by a river, canyon, ocean, etc.)
-The members of each population may
become different, and are then considered
to be different species.
Extinction leads to species
replacement.
-Climate changes or natural
disasters (flood, fires, mud
slides, volcanoes, meteorites)
cause extinctions.
Me,…extinct,…
NEVER!!!
-Species that have become extinct will be
replaced by another species using their
area.
-Results in macroevolution – change that
occurs among species over time as new
species evolve and old species become
extinct (mammals replacing dinosaurs)
What evidence
do scientists
use to prove
macroevolution?
Evidence of Macroevolution
Fossils – preserved or mineralized
remains (bone, tooth, or shell) or
traces (footprint, burrow, or
imprint) of an organism that lived
long ago
ANATOMY & DEVELOPMENT
Vestigial structures
-Body part reduced in size or no
longer functional
Example: whale’s vestigial pelvis
Embryology
--Embryo = early stages of
organism’s development
--Animals have very similar
embryos
Human
Chicken
DNA
-All living things are made of DNA
-DNA shows that some animals
are more closely “related” than
others
-Example: dogs are more closely
related to bears than to fish so
the DNA of dogs is more like bear
DNA than fish DNA
Homologous
structures
-Many structures
of organisms are
similar
-Example: bones
in the human
hand, bat’s wing,
whale’s flipper
Whale’s flipper
Bat’s wing
•Gradualism--rate of evolution
is steady (example: horses)
According to scientists, horses
were first small, had 4 toes, and
sharp teeth (meat-eater)
Eohippus— “dawn horse”
•Punctuated equilibrium-evolution can be rapid and in
spurts (example: elephants)
Darwin wrote: “Can we doubt…that
individuals having any advantage, however
slight, over others, would have the best
chance of surviving and procreating their
kind? … This preservation of favorable
variations, I call Natural Selection.”-----Natural Selection leads to microevolution,
which is the change within a species that
occurs over time.
EVIDENCE OF MICROEVOLUTION
Industrial Melanism in Biston betularia
(peppered moth)
-Light & dark variety of moths present
-Light was predominant before Industrial
Revolution
-Trees darkened w/pollution which
allowed for the dark variety to become
predominant (Read p. 261)
Sickle Cell Anemia (Reveals Evidence
of Microevolution)
If individuals homozygous for sickle cell
anemia die early, then why hasn’t the
allele for that trait entirely disappeared?
Balancing Selection,…in central Africa,
natural selection affects sickle cell anemia
in opposing ways,…(1)it tends to eliminate
the sickle cell allele because it is lethal to
homozygous individuals, and (2)it tends to
preserve the allele because heterozygous
individuals are resistant to malaria.
The sickle cell allele has no benefits for
individuals in the U.S. because we no
longer are faced with malaria. Therefore
the number of people with that allele is
decreasing. When natural selection is
unopposed, the frequency of a particular
allele tends to move in one direction—in
this case, toward elimination. Biologists
call such unopposed selection directional
selection.
Divergence – the accumulation of
differences between groups (populations,
species, genera, etc.)
According to scientists,…
Divergence then leads to the formation of
new species, a process known as speciation.
Ecological races – populations of the same
species that differ genetically because of
adaptations to different living conditions
Reproductive isolation – the prevention of
mating between formerly interbreeding
groups or the inability of these groups to
produce fertile offspring