BIOL 4160 Chapter Notes - Chapter 3: Selective Breeding, Logical Consequence, The Scientists
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Darwinian Natural Selection (Pages 74 – 97)
3.1. Artificial Selection: Domestic Animals and Plants
To increase the frequency of desirable traits in their stocks, plant and animal breeders employ
artificial selection (Example of Darwin and his pigeon’s on Page 74).
o If the desirable traits are passed from parents to offspring, then the next generation,
consisting of the progeny of only the selected mates, will show the desirable traits in a
higher proportion than existed in the previous generation.
o Read example of Tomato on page 74 and 75.
3.2. Evolution by Natural Selection
Darwin realized that a process like artificial selection occurs in nature
His Theory of Evolution by Natural Selection suggests that descent with modification is the
logical outcome of four postulates:
Individuals within populations are variable
The variations among individuals are, at least in part, passed from parents to
In every generation, some individuals are most successful at surviving and
reproducing than others
The survival and reproduction of individuals are not random; instead they are
tied to the variation among individuals. The individuals with the most
favourable variations, those who are better at surviving and reproducing, are
o If these four postulates are true then composition of the population changes from one
generation to the next (see Figure 3.4 on page 76).
o If there are differences among the individuals in a population that can be passed on to
offspring, and if there is differential success among those individuals in surviving and/or
reproducing, then some traits will be passed on more frequently than other.
The characteristics of a population will change slight with each
succeeding generation Darwinian evolution.
o Darwin referred to the individuals who are better at surviving and reproducing, and
whose offspring make up a great percentage of the population in the next generation as
The ability of an individual to survive and reproduce in its environment
An important aspect is its relative nature. Fitness refers to how well an
individual survives and how many offspring it produces compared to others of
Adaptation refers to a trait or characteristic of an organism that increases its
fitness relative to individuals without the trait.
Read on Alfred Russell Wallace (Page 77)
The interesting fact is that the Darwin-Wallace theory’s four postulates and their logical
consequence can be verified independently (testable).
3.3 The Evolution of Flower Color in an Experimental Snapdragon Population
K.N Jones and J. Reithel (2001) did an experiment using 48 snapdragons to see if Darwin’s four
postulates are true.
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