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Lesson # 5: Evolution
(Natural Selection vs. Artificial Selection)
Recall Natural Selection
Adaptation
- A characteristic or feature of a species that makes it well suited for
survival or reproduce success in its environment
- Ex. cold – blooded, fur, large beak size
Natural Selection
- The way in which nature favours the reproductive success of some
individuals within a population over others
- Some individuals would have a better chance of success than others
- Those individual organisms who happen to be best suited to an
environment survive and reproduce most successfully, producing
many similarly well – adapted descendants
- After numerous such breeding cycles, the better – adapted dominate
- Nature has filtered out poorly suited individuals and the population has
evolved
- Favour REPRODUCTIVE success that is produced by
ENVIRONMENT CONDITIONS
How Natural Selection Occurs
- Mechanism by which populations adapt and evolve
1) Variation + Inheritance
Organisms can vary in size, coloration, ability to fight off
diseases, and countless other traits. Such variation is often the
result of random mutations, that arise when cells divide as
new organisms develop
When organisms reproduce, they pass on their DNA--the set
of instructions encoded in living cells for building bodies--to
their offspring. And since many traits are encoded in DNA,
offspring often inherit the variations of their parents.
Ex. Tall people tend to have tall children.
How Natural Selection Occurs
2) Selection (Survival and Reproduction)
 Environments cannot support unlimited populations
 Because resources are limited, more organisms are born
than can survive: some individuals will be more successful
at finding food, mating or avoiding predators and will
have a better chance to thrive, reproduce, and pass on, their
DNA
 Small variations can influence whether or not an
individual lives and reproduces
 Ex. Differences in color, aid some individuals in
camouflaging themselves from predators
 Ex. Sharper eyes and claws help an eagle catch its dinner
 Ex. Brighter coloration improves a male peacock's chances
of attracting a mate
How Natural Selection Occurs
3) Time and Adaptation
 In generation after generation, advantageous traits help some
individuals survive and reproduce
 These traits are passed on to greater and greater numbers of
offspring
 After just a few generations or after thousands, depending on
the circumstances, such traits become common in the
population
 The result is a population that is better suited--better
adapted--to some aspect of the environment than it was
before
 Ex. Animal becomes cold – blooded to survive according to
climate change
 Ex. Scales used for protection change colors to serve as
camouflage
Artificial Selection
- Long before Darwin and Wallace, farmers and breeders were
using the idea of selection to cause major changes in the
features of their plants and animals over the course of decades
- Farmers and breeders allowed only the plants and animals with
desirable characteristics to reproduce, causing the evolution of
farm stock
- This process is called artificial selection because people
(instead of nature) select which organisms get to reproduce
- One of the most important technological innovations in human
history
Domestication
- The changing of members of a species to suit human needs
through controlled captive breeding
Artificial Selection
Artificial Selection
- The directed breeding in which individuals that exhibit
a particular trait are chosen as parents of the next
generation; artificial selection is used to produce new
breeds or varieties of plants and animals
- Artificial because it occurs in captivity rather than in a
natural setting and selection because humans choose
which specific animals and plants are bred
Artificial Selection Examples
- Humans have been domesticating animals and plants for more than
10,000 years
- Earliest animal to be domesticated was the wolf (which are now
dogs)
- Plants are equally capable of being selectively bred to suit our needs
- Ex. wild sea cabbage (differences in taste and appearance)
How Does Artificial Selection Work?
– breeding selected individuals with certain favoured traits will
result in the favoured traits becoming more prevalent and more
pronounced
Independent variable – breeding population (selected by
breeder)
Dependent variable – appearance of favoured trait in the
population
Procedure
1) Choose a useful species that can be bred in captivity
2) Breed a large number of individuals
3) Choose a trait that you wish to favour (i.e. large size, colour,
sweetness)… artificial insemination
4) Identify individuals that exhibit the favoured trait most strongly
5) Breed only these individuals to produce the next generation of
individuals
6) Repeat over many generations
How Does Artificial Selection Work?
Ex. Indigenous peoples domesticated the tomato
- Wild tomato plants produce nutritious but small fruit (exhibited
variability – some larger, smaller, rounder etc.)
- Generations after generations, farmers selected seeds from the
best plants to sow the next season
- The seeds germinated, grew, flowered, and then cross –
pollinated one another, producing more fruit with the desired
traits
- Farmers would save seeds from the best plants for sowing
- These practices happened in many parts of the world
- Continuation
The Power of Artificial Selection
- The most unexpected results of artificial selection is the
production of individuals that exhibit traits that are far
beyond the natural variability witnessed in the original
breeding population
- Ex. giant pumpkin or long horns of the Texas Longhorn
Longest Running Artificial Selection
Experiment
- Illinois agricultural experiment station
- Started in 1896 and is still continuing (over 100 years)
- Testing oil content on corn seeds
- Involved two separate breeding experiments
1) Corn plants were selected for high oil content
2) Corn plants were selected for low oil content
- Over 76 years, the oil content increased from 5% to more
than 18% in the first experiment
- Whereas, it dropped less than 1% in the second
- Evidence proves that the process of artificial selection can
indeed be used to dramatically increase or decrease oil
content in corn seeds