LS Problem Set 2 PDF

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LS Problem Set 2 ! 1.

How did researchers determine whether the snow lotus flowers in China are becoming shorter over time? Is this result/observation sufficient to conclude that humans are causing this change? Why or why not?

Researchers determined whether snow lotus flowers were becoming shorter by measuring the recently sold collections in China and comparing those measurements to other from flowers of different ages. They retrieved data from various field collections that held information about plant biodiversity from around the world. From this, they took measurements of all different ages of snow lotus plants from 8 herbaria collections. Then they made note of the average height of the flowers from prior to 1920 and plants from after 2000. They found the recently collected plants showed a decrease in average height (from 22cm to 14cm). They additionally measured the snow lotus plant from a closely related species that is seldom harvested and this study showed that there was no decline in height. This proved their hypothesis that human harvesting of the taller snow lotus flower is causing evolution through selection of smaller plants. However, this was not enough evidence to come to the final conclusion that humans instigate this change. While they were able to compare the measurements to less harvested flower, they would still need to find out if the flowers not harvested by humans at all - from that same area - are getting smaller too. Although there was a further investigation into the Tibetan flower that was not allowed to be harvested, there could be an element of environmental or regional difference that take influence on the height of the plant too. ! 2.

What two “control groups” did the researchers use in their comparisons with today’s plants? Why do we call these comparison plants “control groups”? In what way do they differ from a control group in a randomized, controlled, double-blind study.

First control group: snow lotus flowers from numerous filed collections and herbaria records! Second control group: plants growing in a protected and sacred area of Tibet where flower harvesting is not allowed. ! These are considered control groups in this experiment because the only difference between them and the recently sold flowers is the fact that they have not been affected by longterm harvesting / human harvesting. There was no

need for randomized, double-blind study because, unlike humans, plants could not be affected or influenced in a certain way. ! 3.

What evidence did the researchers present? Did the evidence support or refute their hypothesis? How much confidence do you have in their conclusions? Why?

Evidence showed that the flowers’ average heights decreased over time from 22cm to 14cm between the time periods of before 1920 to after 2000. Similarly, from the study on Tibetan flowers that were protected, researchers saw that flowers from protected areas held a height of 22.7cm while flowers heavily harvested areas had a mean height of 13.4cm. This strongly supported their hypothesis that human harvesting of the taller snow lotus flower is causing evolution through selection of smaller plants . I would say that I have confidence in this conclusion because there was a significant amount of research and data collected which was relevant to the study. Data was taken over a great length of time and compared to various control groups that further supported their hypothesis. While there still exists the possibility of environmental influence, I am still confident that the conclusion about human harvesting being the major influence is true. ! 4.

Using examples for each, describe natural selection and distinguish it from evolution. Over the course of several decades, plant breeders working with corn crops significantly increased the kernel size and nutrition. Why did this work? If the rate of improvement slows down or stops, what might you recommend they do to improve the results from their selective breeding programs? Why?

Natural selection: It is the change in allele frequencies in a given population. Can be seen as a mechanism for evolution whereby individuals with a greater fitness have the better chance of survival and reproductive success to pass on their genes. ! Evolution: gradual process in which something changes into a different, more complex form ! The corn crops gradually became larger in size because of the specific breeding and directional selection done artificially by the breeders. Breeders would take corn crops with the best nutrition and kernel size and breed them to reduce genetic variation amongst the crops. ! If the rate of improvement slows or stops, they could improve their results by bringing a similar species of the corn crop or one from another region to increase genetic variation and possibly produce better results. Another solution

might be to pick the top 20% of crops that are largest and nutritious and breed those. However, this may have been what the breeders were doing previously thus I would better recommend the first solution given. ! 5.

Among the Old Order Amish of Lancaster, Pennsylvania, there is an unusually high frequency of polydactylism (extra fingers). Since the group was founded by a small group of separatist German Mennonites in the early 1770s, some 61 cases of this rare trait have been reported, about as many cases as in the entire rest of the world since that time. Given that the trait is inherited, how can you explain the high frequency of this trait among the Old Order Amish? Is it the result of natural selection? Why or why not? Be sure to think about the necessary and sufficient conditions for natural selection in framing your answer.

The high frequency amongst the Old Order Amish can be explained by the Founder’s Effect. This is a form of genetic drift which a mechanism for evolution whereby a subset of a population finds a new population. In the case of the Old Order Amish, the German Mennonites were initially a small subset of a larger population that isolated themselves and were not representative of their previous population. This caused an increase in the frequency of the allele for polydactylism. ! This is not a result of Natural Selection because the increase in the allele frequency for polydactylism occurred by random chance event. In Natural selection, the increase in frequency of this allele would de dependent on the beneficial/harmful effects of the allele as well as the increase reproductive success. However, this was not the case. ! 6.

How does modern medicine influence the selective pressures on birth weight in humans? What are the consequences for genetic variation for this trait in human populations?

Modern medicine has reduced the selective pressures on the birth weight in humans. It has allowed babies with either extremely high or low weights to live longer than what they have survived for without this technology. Before this modern technology, there was an element of stabilizing selection whereby the babies with the intermediate weight of 7-8 pounds would live longer therefore reducing the frequency of the allele associated with extreme birth weights in the population. With the technology, there is now the consequence of decreasing the selection against alleles causing high and low birth weights thus reducing their rate of removal from the population. !

7.

Today, approximately 25 million people live at elevations above 10,000 feet, with the highest permanent human settlement at 17,500 feet in the Peruvian Andes. Biological anthropologists have studied the way these people have responded to the physiological problems raised by low oxygen pressure and extreme cold. Studies show that some humans living at high altitudes exhibit the following anatomical and physiological differences relative to populations at sea level. 1) 30% higher red blood cell counts 2) larger right ventricles of the heart Furthermore, populations living at higher elevations (in Peru, Tibet, and Colorado) report higher infant mortality rates, mainly resulting from respiratory infections. Would you hypothesize that evolutionary agents have been at work on these populations? Might several evolutionary agents be combined to produce these results? Is it possible that these changes in physiology and anatomy have not resulted from a change in allele frequencies, and therefore are not evolutionary changes as we have defined them? Explain.

I would hypothesize that evolutionary agents have been at work on these populations as the alleles from humans living at high altitudes have had to adapt to the environment of low oxygen pressure and temperatures. The reproductive cells may have mutated to survive this environment hence the higher red blood cell counts and right ventricle. This is then passed on to the next generation which will in turn show an element of evolution as those children’s alleles will result in high red blood cell counts to survive the higher altitudes. The migration to the higher altitude could also be a cause for the change in allele frequencies. Natural selection also shows evidence of occurring in terms of the variation of a trait and the heritability. The more reproductive success for those with possible lower birth weights, larger red blood cells counts, and larger right ventricles (which lead to improved lung functionality) may have induced an increase in the associated alleles. ! I do not think is is possible that these changes have not resulted from evolutionary causes because the a population will only change both physiologically and anatomically through evolutionary mechanisms that affect both phenotypes and genotypes in a given population over time. !...