Three relationships with the same slope, but different amounts of “scatter” around an imagined best fit line.
A classic example of natural selection:
Paper on industrial melanism.
a. Kettlewell’s primary hypothesis.
b. The different ways Kettlewell tested his hypothesis.
Two methods deserve special attention.
1. Kettlewell's work was the first that used mark-recapture. Mark-recapture, first used to test the effectiveness of natural selection, is now of the most common “experimental” methods used in ecological research. It is important that you understand this method.
.
Calculate the relative fitnesses for typical and melanistic moths in Dorset, England if the number of moths released was 406 melanistic and 393 typical. They recaptured 19 of the melanistic moth marked and 54 of the typical.
d. Determine which type of evidence, frequency distributions (correlations), mark-recapture work, experiments on predation or modeling, best supports Kettlewell’s hypothesis. Justify your answer.
2. Kettlewell also used correlation. Many studies in evolutionary medicine will relay on correlations rather than experimentation.
The experiment has long been accepted as a way to gather evidence for or against hypothesis. Yet often it is impossible to conduct the appropriate experiments to examine major evolutionary questions. Making more observations has always been a legitimate way of testing scientific hypotheses.
Example: Every time the sun sets in the west and rises in the east I am more convinced that it will continue to do so. (reason for the sun rising----http://www.universetoday.com/18117/why-does-the-sun-rise-in-the-east-and-set-in-the-west/)
Correlations are trends, collections of observations, measured by the tightness of fit between two variables. Statistics is often used to determine how closely data points fit to a straight line drawn between them (linear regression).
Three relationships with the same slope, but different amounts of “scatter” around an imagined best fit line.
Lately non-experimental science has been dubbed discovery science. This seems a humble name for methods that have given use major theories in biology such as "the cell theory" and "the grand synthesis or evolutionary theory".
For example, Dr. Snow used observations and correlations to determine the cause of cholera.
An observation based on interviews and city medical records.
"The most terrible outbreak of cholera which ever occurred in this kingdom, is probably that which took place in Broad Street, Golden Square, and the adjoining streets, a few weeks ago. Within two hundred and fifty yards of the spot where Cambridge Street joins Broad Street, there were upwards of five hundred fatal attacks of cholera in ten days. The mortality in this limited area probably equals any that was ever caused in this country, even by the plague: and it was much more sudden, as the greater number of cases terminated in a few hours.
The mortality would undoubtedly have been much greater had it not been for the flight of the population. Persons in furnished lodgings left first, then other lodgers went away, leaving their furniture to be sent for when they could meet with a place to put it in."
A correlative map put together by Snow.
Read the following passage from Snow's work. Why did Snow feel it important to investigate individuals in the area of the outbreak that did not get cholera?
“There are certain circumstances bearing on the subject of this outbreak of cholera which require to be mentioned. The Workhouse in Poland Street is more than three-fourths surrounded by houses in which deaths from cholera occurred, yet out of five hundred and thirty-five inmates only five died of cholera. . . . The workhouse has a pump-well on the premises, in addition to the supply from the Grand Junction Water Works, and the inmates never sent to Broad Street for water. If the mortality in the workhouse had been equal to that in the streets immediately surrounding it on three sides, upwards of one hundred persons would have died. “
“ There is a Brewery in Broad Street, near to the pump, and on perceiving that no brewer's men were registered as having died of cholera, I called on Mr. Huggins, the proprietor. He informed me that there were above seventy workmen employed in the brewery, and that none of them had suffered from cholera--at least in a severe form--only two having been indisposed, and that not seriously, at the time the disease prevailed. “
“ The men are allowed a certain quantity of malt liquor, and Mr. Huggins believes they do not drink water at all; and he is quite certain that the work-men never obtained water from the pump in the street. There is a deep well in the brewery, in addition to the New River water. “
More on natural selection.
a. Experiments are the best test.http://evolution.berkeley.edu/evolibrary/article/side_0_0/tegula_01
b. Correlations suffice, but best if can tie them into predictions. https://evolution.berkeley.edu/evolibrary/news/090301_cichlidspeciation
c. Why do you suppose the following examples are considered examples of natural selection directing the changes observed?
http://evolution.berkeley.edu/evolibrary/article/microexamples_01
Genetic drift is being accepted as a potent force in evolution.
http://evolution.berkeley.edu/evolibrary/article/samplingerror_01 and
http://evolution.berkeley.edu/evolibrary/article/bottlenecks_01
We will work with this simulation on genetic drift to get a feel for randomness. We'll do a class poll to see what is the smallest and largest number of trials before genes are fixed.
http://pages.ucsd.edu/~dkjordan/resources/clarifications/MitochondrialEve.html
and
http://www.cals.ncsu.edu/gn/ex/mit-eve.html
Often simulations are done on a population level. Below are graphs that simulate genetic drift under the gene frequencies and numbers indicated. Can you explain the difference between graphs below?
Current examples of genetic drift as a potent force in nature.
http://evolution.berkeley.edu/evolibrary/news/101201_panthers
http://evolution.berkeley.edu/evolibrary/news/080901_dftd
http://evolution.berkeley.edu/evolibrary/news/070701_cheetah .
Selection or drift: How do you judge?
For larger populations look for evidence of correlation between environmental change and phenotypic change. If not there, look for conditions favorable for potent genetic drift, such as small population sizes, etc.
