13.2 Natural Selection in Action
Further examples of Natural Selection as a driving force for evolution
Point mutation (only one nucleotide has changed) drives evolution of a pathogen
Resistance to anti malaria drugs Fansidar of Plasmodium falciparum in S.E. Asia is due to a point
mutation (single nucleotide changes in DNA sequence of a gene that change he amino acid
sequence of the corresponding protein product).
Both human hosts and Plasmodium parasite require folic acid, an essential vitamin. While we
must obtain folic acid from food, Plasmodium can synthesize its own folic acid.
Effective anti malaria drugs target enzymes in Plasmodium responsible for synthesizing folic
In regions where anti malaria drugs use is rampant, the pathogen populations have high
frequencies of the mutant gene coding for the enzyme (protein), rendering Fansidar ineffective.
Q. Would there be this mutation if human beings had not developed Fansidar as antimalaria
drug? Mutation does not depend on the need of the organisms
Q. if a population of bacteria is exposed to antibiotics, will some bacteria become antibiotic
resistance as a result? (Or if the bacteria were not exposed to antibiotics, would they have the
mutation that can resist antibiotics). ***Know this concept!!! It will be on the final
A. yes, some bacteria will have the mutation to resist antibiotics
B. I do not know, they might or they might not, depending on if the mutant gene that
resist antibiotic already exist in some individuals in this population (if the population does not
have the mutant gene they cannot produce the gene which resists antibiotics—evolution/
natural selection is an editor, not an author. Genes cannot be created in response to
C. I do not know the answer
Adaptive radiation: Hawaiian honey creepers as examples
Hawaii is a perfect place to illustrate the concept of adaptive radiation:
It is the most remote archipelago (a series of islands) on earth, making it very hard for any
terrestrial organisms from anywhere in the world to get to; It is an archipelago, as opposed to a single island, thus facilitating populations to be isolated
from one another (and splitting into distinct species);
It is large enough with a great variety of different kinds of habitats, providing niches for
radiation of large number of new species.
It is young but old enough, 5 millions years, for adaptive radiation to achieved maturity.
There used to be over 60 species of honey creepers in Hawaiian archipelago (more than half of
them have gone extinct). All species of honey creepers descended from a single pair or a small
flock of colonists that arrived in the islands many thousands of years ago. The ancestors of
modern day honey creepers were related to goldfinches in North America
The humble beginning of a few ancestral birds bred and propagated. Over time, their
descendants diverged, exploiting the various niches available to them, and eventually became
distinct species different from one another.
Overhunting, deforestation, rats, carnivorous ants, avian malaria have wiped out most of these
species unique to Hawaii. Honey creepers are endemic to Hawaii, found only in Haw