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Title: The Evidence for Evolution
Description: Biology 101 notes on the evidence for evolution. Taught by Dr. Bostrom at Marietta college.
Description: Biology 101 notes on the evidence for evolution. Taught by Dr. Bostrom at Marietta college.
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Chapter 21 The Evidence for Evolution
Beaks of Darwin’s Finches
Darwin collected 31 specimens from 3 islands in the Galapagos Islands
-Darwin not an expert on birds
-Took them back to England for identification
-Told his collection was a closely related group of distinct species
-All were similar except for beak characteristics
-In all, 14 species now recognized
Adaptive radiation----character displacement
Natural selection
Modern research has verified Darwin’s selection hypothesis
3 conditions of natural selection
-Variation must exist in the population
-This variation must lead to differences among individuals in reproductive success
-Variation among individuals must be genetically transmitted to the next generation
The grants
-Studied medium ground finch on Daphne Major
-Found beak depth variation among members of the population
-Average beak depth changed from one year to the next in a predictable fashion
*Droughts: birds with deeper, more powerful beaks survive better
*Normal rains: average beak depth decreased to its original size
When the environment changes, natural selection often favors different traits in a species
Adult Biston betularia come in a range of shades
-Body color is a single gene
-Black individuals have the dominant allele
*Rare in the population until 1850’s
*From that time on, frequency increased to near 100%
J
...
Tutt hypothesized that light-colored moths declined because of predation
Light moths were easily seen by birds on darkened sooty trees
Confirmed with separate field studies with a variety of experimental designs (keetlewell)
Industrial melanism
Phenomenon in which darker individuals come to predominate over lighter ones
-other moths in other industrialized areas showed the same trend to darken
Pollution control resulted in bark color being lighter again
Light-colored peppered moths now are dominant in the population
Agent of Selection?
Tutt’s hypothesis about the agent of selection is currently being reevaluated
The current reconsideration of the agent of natural selection illustrates well the way in which scientific
progress is achieved
Hypotheses, such as Tutt’s are put forth and then tested; if rejected, new hypotheses are formulated,
and the process begins anew
Artificial Selection
Operates by favoring individuals with certain phenotypic traits, allowing them to reproduce and pass
their genes on the next generation
Drosophilia melanogaster
Selected fruit flies with many bristles on abdomen
At the start average number of bristles was 9
...
Evolution is not solidly demonstrated
*Just a theory like the theory of gravity
2
...
The intelligent design argument
*Too complex for a random process
*Natural selection is not random but it is not directed
4
...
Proteins are too improbable
*Probability of hemoglobin as random event = (1/20)141
*Can’t argue backwards – what are the odds of students having the birthdays they do in
class
6
...
The irreducible complexity argument
*Intricate machinery of cell cannot be explained by evolution from simpler stages
*Natural selection can act on a complex system because at every stage of its evolution,
the system functions
Title: The Evidence for Evolution
Description: Biology 101 notes on the evidence for evolution. Taught by Dr. Bostrom at Marietta college.
Description: Biology 101 notes on the evidence for evolution. Taught by Dr. Bostrom at Marietta college.