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Steve Symeonides
4/18/2012
Period 1,4,6,7
Biology
4 STEPS TO NATURAL
SELECTION
Overproduction
Competition
Variation
Evolution through Natural Selection of Genes and
Adaptation to the Environment
1- More individuals will be born than will survive and reproduce.
(OVERPRODUCTION)
( Meaning that there aren’t enough resources like food, shelter, water, or mates for
everyone)
2 – Because there aren’t enough resources for all to survive and reproduce, there will
be competition between individuals for resources and mates.
(COMPETITION)
3 – There is Genetic Variation among individuals in a species. Some of these genetic
differences will help (or hurt) their owners as they compete for resources or mates.
(VARIATION)
Selection and 4 – On average, individuals with better combinations of genes (genes that help them
Adaptation survive in their habitat better) will survive and reproduce more often. Helpful genes
will spread through the species over many generations. Other genes will become less
common.
(NATURAL SELECTION or ADAPTATION)
Adaptations (This means that as the good genes are passed on, the population changes to better
fit their habitat- these changes are called adaptations, characteristics that help a
species fit their environment. For example camels have long eyelashes that keep
sand out of their eyes and nostrils that they can close tightly to keep sand out of their
nose and keep from drying out – adaptations to living in a desert.)
evolution As natural selection continues, whole species can change in form. If a population of a
species changes enough, it can become a whole new species. This is evolution- the
change in form of an entire species as it adapts to a changing environment.
Summarize
What four things must happen for natural selection to occur?
That is the difference between natural selection and evolution? (hint: how many
organisms are does selection work on at a time, what about evolution?)
Steve Symeonides
4/18/2012
Period 1,4,6,7
Biology
EVIDENCE FOR NATURAL SELECTION
AND EVOLUTION
EVIDENCE TYPE 1 - ARTIFICIAL SELECTION
Artificial Selection,
Selective Breeding
Artificial Selection, or Selective Breeding is when humans, rather than nature, choose
which organisms and genes they want to become more common.
Examples are all of the livestock and dog breeds, plus nearly every food that we eat.
Why artificial selection
helps support the idea of
evolution by natural
selection.
Artificial selection happens when humans allow only organisms that show specific
genetic traits to breed.
(for example, dairy farmers have chosen their breeding stock from animals with
genes for high milk production, high fat content to the milk, strong frames, high
udders, etc.)
Artificial selection by selective breeding was an important evidence for natural
selection because people were already familiar with the idea. They had experienced
changes in species, made through selective breeding programs, in their farm and
domestic animals, and in many of the plants that they grew, both for food and in their
gardens. This made the idea easy to accept.
The Fossil Record
EVIDENCE TYPE THE FOSSIL RECORD
Fossil
Fossils are the preserved remains, or evidence, of organisms that lived long ago.
Organisms can be petrified
(replaced by stone)
Different types of fossils
trapped in amber
(hardened tree sap)
Steve Symeonides
4/18/2012
Period 1,4,6,7
Biology
Leave behind trace fossils or
like tracks or tunnels
molds (a print in the rock
where the organism was)
More Fossil Types
Sometimes we find preserved remains, when cold dryness or acid, keep
bacteria
from decomposing them. In this case, what you are finding are the actual remains of
the organism, preserved in acid, ice, or by drying out.
Steve Symeonides
4/18/2012
Period 1,4,6,7
Biology
Fossils show changes in species and groups of species over time.
Transitional fossils are very important, because they show intermediate forms,
Transitional forms species that have characteristics of both older groups and newer ones.
This is a fossil of Archaeoptyrix a small dinosaur that had feathers like a bird, but few
other bird characteristics.
It is a transitional form between
dinosaurs and birds showing the
early evolution of the group.
Fossils also show that many species
have become extinct as
environments change. The fossils
show that as species go extinct they
are replaced by others that are
better adapted to the environment.
Why the fossil record
supports the theory of
Evolution
Fossils give important evidence of evolution because they make clear that species
both change and can go extinct over time. Fossils also provide us with transitional
forms that show species such as feathered birds and whales with legs, that are in
between older and newer forms.
Steve Symeonides
4/18/2012
Period 1,4,6,7
Biology
EVIDENCE TYPE 3 - Homologous structures
Homologous structures are parts of organisms that are made from the same body
parts (muscles bones, scales etc.), but have become adapted for different uses.
Homologous Structures
Are made from the same Homologous structures show how adaptation and evolution change a body to fit
Body parts but do different different habitats. This is because they show how the same bones, muscles, skin, and
jobs (e.g. a bird wing and a organs have evolved to serve different purposes in different groups of species.
human arm).
(The most commonly used example is the arm of a human, the front leg of a horse,
the fin of a fish, the flipper of a whale and the wing of a bat. All of these are made
using the same bones and muscles. But depending on their habitat, the bones, and
the muscles surrounding them have changed to fit the species’ environment and
niche.
Steve Symeonides
4/18/2012
Period 1,4,6,7
Biology
Another good example of homologous structures are the many different forms leaves
take in plants.)
How homologous
structures support the
theory of evolution.
Homologous structures support the theory of evolution because they show that the
same body parts can be adapted to take many different forms depending on the
environment. The flipper of a whale serves it much better in the water than an arm
and hand would. So as the ancestors of whales spent more and more time in the
water, their front legs evolved into flippers (do a search on “whale transitional forms”
for more info.
Steve Symeonides
4/18/2012
Period 1,4,6,7
Biology
EVIDENCE TYPE 4 - Analagous Structures
Analogs are things that are made of different parts, but do the same job, like an
hourglass, a sundial and a watch.
Analagous structures
Analagous structures are body parts that do the same thing, but are made up of
different parts.
One of the best example comes from flying animals,
Bats, birds and insects all have wings, but they are made of different structures. Bird
Analogous structures
are made from different wings are arms, bat wings are hands and insect wings don’t even have bones.
body parts, but do the
same job.
Analogous structures are important because they show that, given the same
evolutionary pressures (or opportunities), similar structures can evolve to fit the
purpose – even when using different body parts to do it. (In this case wings evolved
to give different groups the advantages an animal gets by being able to glide or fly
through the air.)
Another example would be all of the different body parts that have evolved to
push an animal through water – the flukes of a whale, the tail fin of a fish, the
webbed feet of a duck, the body of a snake, even the wings of a penguin, all are parts
adapted to let an animal move through water to find food. Natural selection chose
body parts that were better shaped to move through water and slowly those parts
evolved into new shapes and forms – for example from a bird wing to a penguin’s
flipper.
Steve Symeonides
4/18/2012
Period 1,4,6,7
Biology
EVIDENCE TYPE 6 – DNA AND GENETICS
You can look at DNA sequences in different species and compare them to
see how closely related they are. Species that are closely related have
nearly identical spellings of genes.
Also you can look at genes that are in many different groups of species
and compare the DNA sequence of the genes to see what groups are
related to each other. You can look at the changes in the gene and figure
out its history by the changes in the spelling of the gene.
Steve Symeonides
4/18/2012
Period 1,4,6,7
Biology