Download A105 exam 1 essay 3

Essay 3
We were looking for 3 pieces of information in answers to this question:
1) An explanatory answer to the question "are humans subject to natural selection?"
2) An awareness of natural selection as a PROCESS by which genes become fixed in a
population
3) More than one example that supported the position taken in (1).
• A 10/10 paper did an outstanding job explaining and integrating all parts of the
question, particularly (2), and included specific, well-written explanations of at least
two good examples.
• An 8-9 paper contained all pieces of information and had at least 2 examples, with at
least one of them being good. It was also possible to get up to an 8 with just one
example, provided that the example was really good.
• A 6-7 paper contained (1) and either (2) and one example or at least two fair
examples.
• A 4-5 paper contained (1) and either (2) or one example.
• A 1-3 paper contained (1) and no examples.
The best answers didn’t just list the examples but explained the process of how natural
selection worked in each example, and compared them.
Essay 3
10/10
Humans, like any animal, are subject to natural selection. Natural selection occurs when
three factors are present: species have heritable traits that vary between individuals, more
offspring are produced than can survive (competition), and heritable traits bestow an
advantage on those individuals who possess them in their environment. Humans all vary,
genetically, in terms of their resistence to disease, for example. With diseases and new
strains of bacteria, competition is present, just as it has always been. Certain humans also
display differential reproductive success, allowing them to inherit traits to aid in survival.
Natural selection continues to occur in humans. For example, people who live in areas
with widespread malaria outbreaks frequently carry the sickle cell gene, a small genetic
mutation which influences the ability of Hemoglobin protein in red blood cells to carry
oxygen. Homozygous sickle cell is often fatal. But heterozygotes for this trait can
survive infection by the malaria virus. Those who carry this gene are able to survive and
pass it along to their offspring. Those who do not carry the gene fall victim to malaria and
have a higher risk of dying. Natural selection acts on the individuals, affecting overall
genetic frequencies in populations, which causes microevolution through time. Another
example is cystic fibrosis. This inherited disease produces a thick mucus which fills the
lungs. While this seems quite negative, it actually aids in preventing death from
Tuberculosis. Therefore natural selection caused an increase in the carrying of the cystic
fibrosis gene in areas or times where TB was a danger. This appeared during the
industrial age in England.
Essay 3
7/10
Humans are subject to natural selection. Although natural selection in animals is more
primary, evidence of it in humans is undeniable. Very clear examples are ones of
heterozygous disease genes. There exist many instances where being heterozygous for a
disease can be favored. Cystic fibrosis, for example, as a heterozygous trait gives
resistance to Tuberculosis. As well sickle cell anemia does with malaria. These diseases
would have been eradicated like diseases of the past except for the fact that they favor
reproduction and survival in their respective disease-ridden areas. Some may argue that
humans do not go through natural selection due to medical advancements. These
advancements are, in fact, natural and contribute to natural selection – curable diseases
allow the victim to live, and not-curable still die. That may be a bit different than
traditional natural selection, but it is only a way natural selection has kept current with
our technological advancements.
Essay 3
5/10
Humans are definitely subject to natural selection. I know this from the readings and
lectures about people that are lactose intolerant. People that live in the swiss region are
more likely to digest milk because milk is a major part of there diet. The gene (lactase)
that recognizes milk in the system is less likely to shut down when milk is a major part of
that person’s diet. People in east Asia are less likely to be able to digest milk when they
get older because milk isn’t a key part in their diet. Another natural selection in humans
is the sickel cell desiese. People with sickel cell are less likely to get malaria. So people
in the regions were there are a strong case of malaria are probably not threatened by
sickel cell.
Essay 3
2/10
Yes, natural selection is the process that there is change over time. Every human is
subject to change, but people don’t evolve, populations do. Examples are such as hair
styles. Some hair styles were pretty popular in the 80’s, but you don’t see a lot of those
styles any more. The variation of genes or infectious disease that that may have been a
problem before but is not in todays world. It does not take one person to evolve but a
whole population for evolution.