Classical example: Industrial melanism----Link to study
Background on Malaria
https://www.cdc.gov/malaria/stories/unwanted_souvenir.html
Malaria was once endemic to North Carolina
For Homework
View this film on the work that initially was used to correlate the sickle cell trait with increasing probability of contracting malaria because of prevalence in certain area of vectors.
http://www.hhmi.org/biointeractive/making-fittest-natural-selection-humans
a. What is sickle cell anemia?
b. How was the correlation between sickle cell and malaria confirmed?
c. What does the sickle cell mutation tell us about how natural selection works?
The influence of malaria on human biology is evidenced by the number of other "resistent" phenotypes that have evolved.
For example, persons who are negative for the Duffy blood group have red blood cells that are resistant to infection by P. vivax.
The prevalence of hemoglobin-related and other blood cell disorders, such as Hemoglobin C, the thalassemias and G6PD deficiency, are more prevalent in malaria endemic areas and are thought to provide protection from malarial disease.
Two potential presentation topics.
Heterozygote advantage (not on exam)
Present resistance as reshaping of responses to past pressures
https://evolution.berkeley.edu/evo-news/ghosts-of-epidemics-past/
https://evolution.berkeley.edu/the-relevance-of-evolution/medicine/hiv-the-ultimate-evolver/
Graphs using real data from natural populations can be used to estimate the “strength or potency" (rate of change through time) of natural selection.
Classical example: Industrial melanism----Link to study
Selection can be strong. Rates of changes, from slopes of simulations, of 0.3 to 0.5 have been estimated for industrial melanism and pesticide resistance. When the dark form comprises about 10 per cent of the population, it could jump to 90 per cent in as little as 15 or 20 years.
Most estimates for rates of change, especially for humans, are lower.
For example, the lactose-tolerant allele spread from very low frequencies to high frequencies in less than 9000 years, with an estimated rate of change of 0.09-0.19 for one Scandinavian population.
Today, most field researchers prefer to use selection or fitness gradients.
The trends are the same
.
Surprisingly there is little evidence for negative selection. These are sites that do not appear to be drifting at high rates.
Why are these "traits" being conserved?
It could be an effect of population size or structure. But the reasons could also be that the genes identified have piggybacked on other positively selected genes or their effects (the selected phenotype) or selective agents have been improperly defined. Birth rates are decreasing for humans, researchers are divided as whether this will increase or decrease the potency of selection on traits.
A note on artificial selection
Artificial selection (goal oriented selection) was considered evidence by Darwin for comparable scenarios in natural selection.
An example of how artificial selection is currently being used by evolutionary engineers to develop molecules that one day may prove useful to the biomedical field
https://evolution.berkeley.edu/evolibrary/article/ellington_01
For those interested: Bioengineering with RNA
