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Transcript
Biology 11
Name: __________________
Unit 2: Evolution
M. Harvey 2014
Date: ____________
Darwin’s Theory of Evolution notes
 Over time, natural selection results in changes in the inherited
characteristics of a population.
o Population: A group of individuals of the same species occupying a given area at
a certain time.
o A theory is a well-supported, testable explanation of natural phenomena that
has been supported time and time again with every experiment.
o After Darwin returned to England in 1836 he filled notebooks with his ideas
about species diversity and the process that he would later call evolution
o He did not rush to publish his ideas because they disagreed with the
fundamental scientific and religious beliefs of his day.
o He asked his wife to publish his ideas when he died
o In 1858 another naturalist Alfred Russel Wallace, wrote an essay describing his
work in Malaysia that summarized the same ideas Darwin had been thinking
about for 25 years
o Wallace inspired Darwin to publish the results of his work
o In 1859 On the Origin of Species presented evidence and proposed a
mechanism for evolution that he called natural selection
Five parts to Darwin’s Theory
1. Genetic Variation in Populations
2. Too many Offspring
3. Struggle for Existence
4. Survival of the Fittest
5. Next Generation
Biology 11
Name: __________________
Unit 2: Evolution
M. Harvey 2014
Date: ____________
1. Genetic Variation in Populations
o Genetic variation is found naturally in every trait in all populations
o Two sources of variation
i.
Sexual reproduction

An organisms survival depends in part on the traits the inherit

Sexual reproduction “shuffles the deck”

Mixes the genes and recombines the alleles within a population and
creates unique individuals

During sexual reproduction each parent randomly donates only one
copy of the allele (in the egg/sperm) of each gene to the offspring

Sex cells are haploid (half the amount of genetic information), all
other cells are diploid (full amount of genetic information)

One haploid cell from the mother, one haploid cell from the father
Example: Pea plant height
Parents
In egg or sperm
TT x tt
T T
t t
TT x Tt
T T
t t
Tt x Tt
T t
T t
Offspring’s Genes?
Tt
TT or Tt
TT, Tt, or tt
Offsprings Height?
Tall
Tall
Tall or Short
Example: Flower colour
Punnett square
Biology 11
Name: __________________
ii.
Unit 2: Evolution
M. Harvey 2014
Date: ____________
Mutation

Mutations are any permanent inheritable changes in DNA

The DNA of an organism determines all of its characteristics (structural,
physiological, and behavioral) by coding for the production of the
proteins specific to it  the genetic code.

Most mutations are harmful, a few have no effect, and very rarely they
can be beneficial

Mutations occur at a rate of about once every million cell divisions
 Can be caused by random unpredictable mistakes
 Viruses
 Mutagens (chemicals or radiation)

Only mutations that occur in the sex cells (sperm or egg) are important
to the evolutionary process because only they can be passed from
generation to generation.
o Members of a population vary extensively in their characteristics which
makes them diverse
o No two individuals are exactly alike
2. Too many Offspring
o In nature, more offspring are produced than
are needed to replace the parents
3. Struggle for Existence
o Resources are limited, so members of each species
must compete for food, space, and other resources
o Some organisms in a population are less likely to survive
Biology 11
Name: __________________
Unit 2: Evolution
M. Harvey 2014
Date: ____________
4. Survival of the Fittest
o Some organisms are better adapted

Possess a genetic variation that improves its fitness
o Adaptation is any inherited characteristics that increase an organism’s
chance of survival
 Structural adaptations
 Physiological adaptations
 Behavioural adaptations
o Fitness is the ability of an individual to survive and reproduce in its specific
environment
o Fitness is not the strongest, it is the best adapted
o Organisms which are better suited to the environment will survive and
reproduce, passing on their genes
o Example: Australian Yellow-bellied three toed skink (Saiphos equalis)

coastal skink lays eggs to reproduce

same species living in the higher, colder mountains are
almost all giving birth to live young
o Natural selection does not grant organisms what they need
o If an environment changes over time, organisms who are born with and
adaptation that is beneficial in the new conditions, it will be more likely to
survive (example: peppered moth)
Biology 11
Name: __________________
Unit 2: Evolution
M. Harvey 2014
Date: ____________
5. Next Generation
o The next generation of organisms will be more likely to have that
advantageous trait
Descent with Modification
o Darwin used the term descent with modification (not natural selection)
o Descent with modification suggests that each species has descended, with
changes, from other species over time
o This idea suggests that a living species are related to each other and that all
species, living, and extinct, share a common ancestor
o Therefore, populations change over time
Flaws in Darwin’s Theory
1. Darwin himself recognized 2 problems with his evolutionary theory:
1. He couldn’t explain where the variations in traits were coming from.

Solution/support:
 Mendel  Father of Genetics
 DNA and Genes
2. He could not show a single example of evolution currently occurring
(usually such a slow process).

Solution/support:
 English Peppered Moth