4 Processes of Evolution Assignment (Chapter 4)
Which Process of Evolution is most likely impacting the following populations?
The goal of this assignment is to aid you in understanding how the four processes of evolution work to change populations over time. Before you start this exercise I recommend that you first memorize the definition for each process. I generally encourage students to put definitions in their own words rather than memorize them but for many of the concepts in physical anthropology the words often have specific meanings that can’t easily be replaced with other words. Make sure you read through the examples in your text and understand how each process works to change populations over time.
1. Read through each problem and identify the specific process of evolution that is most likely affecting the population. State which process of evolution you think is most likely and then give a couple of sentences explaining WHY you think that process could be responsible for the change.
Hint: As you read through the problems refer back to the definition for each process of evolution. You should be able to come up with a match. The biggest stumbling block I see students face is that they try to come up with “what if” scenarios. Don’t extrapolate beyond the information that is given. Just work to match the description of evolution with the example given.
– For gene drift make sure to delineate which aspect of gene drift is likely affecting the population (sampling error, fission/fusion, bottleneck).
– For problem four there are two questions- make sure to answer each one.
2. Turning in your assignment: Turn your work in the Submissions Box (not as an attachment) by the due date. You must have several sentences for each problem to explain WHY you picked the process that you did.
3. Last Step for the Assignment: Read my notes and comments at the end of the assignment.
Processes of Evolution Problems
1. Physical anthropologist Eva Hernandez visits the Yamomamo in Venezuela and finds that only 3 individuals in a small village of 85 people have blood type A. Her grandson, Alberto Hernandez, returns 45 years later and finds that no one in the village has type A blood. Which process of evolution is likely affecting this population?
2. The allele that causes an altered form of hemoglobin occurs in all human populations as a result of mutation. Individuals who have one allele for this condition have an increased resistance to malaria. Individuals with two alleles for this condition have significant medical problems and die young. This allele has been found in high numbers in certain populations in West Africa, Southeast Asia and Greece. Why would this allele be in such high numbers in certain populations?
3. In 1959 Daniel Yuh set up a long term study of cataloging the blood types of a group of hunter-gatherers in the Brazilian rainforest. In 1959 he found there were no individuals with blood type B. Three generations later, after this group had begun exchanging mating partners with another group, there were several members with blood type B. Which process of evolution is likely affecting this population?
4. Britain’s Queen Victoria was a carrier for the allele that causes hemophilia and she passed this allele on to some of her descendants. However, there is absolutely no evidence of anyone in
Queen Victoria’s ancestry having hemophilia. What is the most likely explanation for her possessing the hemophilia allele? Which process of evolution likely led to some of her descendents having this allele?
5. The inhabitants of the island Tristan de Cunha are all descended from one indigenous family and a few sailors. The incidence of a rare eye disorder is much higher in these islanders than in other human populations. Presumably, at least one of the original island settlers carried the allele of the trait. The disorder has an abnormally high frequency in this small population because many can trace descent from this one member of a small group of colonists. Which process of evolution likely affected this population in regards to this trait?
Once you have completed the exercise and turned in your work check yourself below. Remember, I am grading you more on following the instructions and completing your work than being completely accurate. Your goal should be to make sure you are learning the material and can apply your understandings to the assignments.
Processes of Evolution Review/Answer Sheet
1. GENETIC DRIFT, specifically Gamete Sampling/Sampling error. Gene Drift is defined as random fluctuations from one generation to the next and in a small population this can lead to an allele going up to 100% or 0% through a random fluctuation of alleles from one generation to the next.
2. NATURAL SELECTION is the only process of evolution that is directional and leads to the selection for individuals with certain traits. This problem is describing sickle cell anemia. If an individual has one allele for sickle cell they have an increased resistance to malaria, which is a leading cause of death in many geographic areas. If an individual has two alleles for sickle cell it is always negative and will affect their longevity and reproductive fitness. In some human populations it has been documented that the rates of the sickle cell allele will fluctuate in relationship to the threat of malaria.
3. GENE FLOW refers to the exchange of alleles between populations. The allele distribution changed as members exchanged mating partners with another group.
4. MUTATION, a random change in the genetic code is the most likely explanation for the appearance of the hemophilia allele in Queen Victoria. There is no history of hemophilia in Queen Victoria’s ancestry prior to her. GENE DRIFT, specifically gamete sampling is the most likely explanation for the high rates of the allele in her offspring and the subsequent generations. In small breeding populations (the royal families inter-bred a great deal, first cousin marriages were the norm) allele frequencies can fluctuate dramatically (from zero to one hundred percent).
5. FISSION and FOUNDER EFFECT, a form of gene drift which occurs when a group of individuals separates from its original population. Founder effect occurs when the break away group has a trait in high numbers due to a random distribution and sampling error. The example from problem five is a real life example as is the problem with Queen Victoria.