Download Natural Selection ppt

Intro to Natural Selection and
Evolution
• With your deskmate, brainstorm anything
and everything you know about evolution
or anything related to evolution
• Before we even begin discussing
evolution, let’s clear up any
misconceptions you may have of
evolution and its associated topics.
Questions
• Where did earth’s organisms come from?
• Why are there so many different kinds of
organisms?
• How did organisms come to be so
apparently well-designed to live where
they live and do what they do?
– Just a few questions that arise when looking
at evolution.
Evolution
• Evolution= change over time
– said to be “the biological history of life on
earth”
• Evolution is not just a change, it has to be
a change in genetic inheritance.
Fact and Theory
Evolution is a fact. How evolution occurs is a
theory.
• Fact (evidence or observation)
– Changes occur in the frequency of alleles within
a gene pool from one generation to the next.
The gene pool is the set of all genes in a species
or population.
• Theory (explanation based on the evidence)
– life has developed (not 'progressed') from one or
a small set of common ancestors as well as from
'simple' organisms to more 'complex' creatures
over the span of geological time.
Adaptation
• Modification of an organism or its parts that
makes it more fit for existence under the
conditions of its environment
– Fit= success at producing fertile offspring
• These organisms will be well-suited to their
environment
– Unfit= not successful at producing offspring
• These organisms’ traits will become less and less
common because they are not being passed down into
the next generation!
Extinction occurs when previous adaptations are no longer
suitable to a changed environment.
Charles Darwin
• From 1831 to 1836 Darwin
served as naturalist aboard the
H.M.S Beagle on a British
science expedition around the
world.
Galapagos
Islands
Natural Selection
• Darwin’s findings and views on natural
selection were written in his book On the
Origin of Species
Natural Selection Assumptions
1.
There is variation in traits.
For example, some beetles are green and some are
brown.
2.
There is differential reproduction.
Since the environment can't support unlimited
population growth, not all individuals get to reproduce
to their full potential. In this example, green beetles
tend to get eaten by birds and survive to reproduce
less often than brown beetles do.
3. There is heredity.
The surviving brown beetles have brown baby
beetles because this trait has a genetic basis.
4. End result:
The more advantageous trait, brown
coloration, which allows the beetle to have
more offspring, becomes more common in the
population. If this process continues,
eventually, all individuals in the population will
be brown.
Note on natural selection
• Natural selection will select against certain
traits
– Hence other traits are favored because they
are not selected against.
• In our beetle example:
– Green beetles were selected against
– Therefore, brown beetles appear to be “favored”
• Since environmental factors cannot be
predicted, natural selection and
evolution cannot predict the future!!!
Darwin’s Theory of Natural
Selection
• #1 Overproduction
• Organisms tend to have many more than two
offspring so at least some will survive (yet
populations usually do not grow rapidly in the
wild)
#2 Competition - Therefore they
must compete for resources
(food, space, mates)
• #3 Variation - variation
within the population
due to random
mating.
• #4 Adaptation Therefore some of them
must be better adapted
to their environment
• #5. Natural Selection- the ability of
organisms that are best adapted to survive and
reproduce . Those that are less well adapted will
not survive.
Homework
Answer in complete sentences!
1. What is difference between fact and
theory?
2. How did organisms become so
apparently well-designed to live where
they live and do what they do?
3. Which of the following is an adaptation:
the sharp teeth of a house cat, or a scar
on the cat’s ear? Explain
4. What are your views on evolution?