Fall 2010 Take-Home EXAM

Heather Blair

CI519 SSM: SCIENCE

Fall 2010 Take-Home EXAM

PART I

Question 1

Consider the following issue, and describe how you would address it in your class and your reasons for doing so:

In a high school Biology class, students organized a debate where both groups used Darwin’s Theory of Natural Selection to defend their respective positions regarding “human nature”. Their arguments are as follows:

Position A: Humans are fundamentally selfish, or in the words of Thomas Hobbes “nasty, brutish, and short”. The reason for this is that natural selection is about the ability of INDIVIDUAL members of a species to survive. It is the individual’s genes that must be passed on. All of evolution is aimed towards insuring that individuals adapt to survive so that they may reproduce. Consequently, “survival of the fittest” means that individuals who survive are the fittest to survive. Hence, self-interest prevails.

Two examples: Animals: Some fish and birds will eat their young. People: In 1816 a French frigate, Meduse, sank in the Atlantic while 147 people escaped on a raft. After 12 days only 15 remained to be saved. The others were either thrown overboard or killed and eaten by the strongest survivors.

Position B: Humans, like other species are fundamentally altruistic and self-sacrificing. The reason for this is that “survival of the fittest” is a designation intended for entire species and not individuals. Maximization of the probability of survival of the gene pool of the species is the appropriate interpretation of Darwin’s Theory of Natural Selection. Furthermore, this is apparent in humans and other species.

Two examples: Animals: A worker bee will sting an invader to a hive even though it will die in the process. Humans: During Robert Scott’s expedition to the South Pole (1911-1912), Captain Lawrence Oates walked out into the snow to certain death, so as not to be a burden to other members of the expedition.

Background

Individuals whose characteristics are will-suited to their environment survive. Individuals whose characteristics are not well suited to their environment either die or leave fewer offspring. This principle is called “survival of the fittest.” (297)

(Miller & Levine, 2000)

The fact that less-fit individuals of a species do not survive helps keep the species from covering the Earth. (297)

(Miller & Levine, 2000)

In his original formulation, Darwin broke the process of evolution by natural selection into four simple postulates, or steps in a logical sequence:

1.  The individual organisms that make up a population vary in the traits they possess, such as their size and shape.

2.  Some of the trait differences are heritable, meaning that they are passed on to offspring genetically. For example, tall parents may tend to have tall offspring.

3.  Each generation, many more offspring are produced than can possibly survive. Thus, only some individuals in the population survive long enough to produce offspring; and among the individuals that produce offspring, some will produce more than others.

4.  The subset of individuals that survive best and produce the most offspring is not a random sample of the population. Instead, individuals with certain heritable traits are more likely to survive and reproduce. Natural selection occurs when individuals with certain characteristics produce more offspring than individuals without those characteristics. (490)

(Freeman, 2008)

Today, biologists usually condense Darwin’s four postulates into two statements that communicate the essence of evolution by natural selection more forcefully: Evolution by natural selection occurs when (1) heritable variation leads to (2) differential success in survival and reproduction. (490)

Freeman, S. (2008).

Evolution is defined as a change in allele frequencies in a population over time. (490)

Freeman, S. (2008).

The biological meaning of adaptation, like the biological meaning of fitness, is quite different from its normal English usage. In biology, an adaptation is a heritable trait that increases the fitness of an individual in a particular environment relative to individuals lacking the trait. Adaptations increase fitness – the ability to produce offspring. (491)

Freeman, S. (2008).

When natural selection occurred, the individual cells did not change through time; they simply survived or died, or produced more or fewer offspring. This is a fundamentally important point: Natural selection acts on individuals, because individuals experience differential success. But only populations evolve. Allele frequencies change in populations, not in individuals. (493)

Freeman, S. (2008).

Clarifying common misconceptions about how natural selection works:

1.  Selection acts on individuals, but evolutionary change occurs in populations

2.  Evolution is not goal-directed or progressive

a.  Under evolution by natural selection, there is no such thing as a higher or lower organism.

3.  Animals do not do things for the good of the species

a.  Individuals with self-sacrificing alleles die and do not produce offspring. But individuals with selfish, cheater alleles survive and produce offspring. As a result, selfish alleles increase in frequency while self-sacrificing alleles decrease in frequency. This, it is not possible for individuals to sacrifice themselves for the good of the species. (496-497)

Freeman, S. (2008).

Evolution is the change in allele frequencies over time. This occurs in four observable ways in nature: natural selection, genetic drift, gene flow and mutation

1.  Natural selection is the process by which individuals with certain heritable traits tend to produce more surviving offspring than do individuals without those traits, often leading to a change in the genetic makeup of the population.

2.  Genetic drift is any change in allele frequencies due to random events. This causes allele frequencies to drift up and down randomly over time, and eventually can lead to the fixation or loss of alleles.

3.  Gene flow is the movement of alleles between populations; occurs when individuals leave one population, join another, and breed.

4.  Mutations are any change in the heredity material of an organism (DNA in most organisms, RNA in viruses).

(Freeman, 2008)

Evolution occurs not on an individual basis but rather on a population of species. Therefore one organism alone cannot evolve in its lifetime and cause an evolutionary change on the species level. In order for evolution to occur by any of these four processes, an adapted characteristic must occur on an individual level and the adaptation must be passed on to its offspring through heritable traits.

Many food industries today practice a process of artificial selection. For the desired product, workers purposely do not use and/or discard those organisms with less desirable traits but mate those organisms with more desirable traits. Consequently, the offspring produced will most likely possess the desirable traits. For example, similar cows that produce larger quantities of milk than others are forced to mate (artificially of course) and produce offspring that yield large quantities of milk. The cows that produce less milk or lack the ability to fill a certain quota are more or less discarded therefore their characteristics are not passed on to offspring.

A similar process occurs in nature, but naturally rather than artificially. Depending on the environmental conditions where certain organisms inhabit, the organism that manages the conditions better and is able to produce more offspring is usually naturally selected for. If there were black and white bunnies in the snowy terrain of Alaska, the white bunnies are better adapted to the environment. Since the snow is white and their fur is white, they are more camouflaged with the environment and therefore less detectable by predators. On the other hand, predators because of the black fur against the white snow can see the black bunny easier. In this case the white bunny has a better chance of survival than the black bunny and will most likely produce more offspring with white fur.

The white and black bunny case exemplifies “survival of the fittest.” When explaining his findings, Darwin used the word “fit” to describe an individual’s ability to survive and produce offspring. As a result, the individuals that are more fit are better adapted to the environment. In the previous example, the white bunny is more fit. Because they have a better rate of survival, they have a higher chance of producing offspring with white fur. Darwinian fit is defined differently than what is found in common language. Instead of strength, “survival of the fittest” illustrates a higher probability of an individual to survive, reproduce and pass its heritable adaptive traits to its offspring.

Finally, evolution occurs on a population level. Although the four mechanisms of evolution occur fundamentally at the individual level, individuals that adapt and pass adapted traits to their offspring, drive evolution on the level of their population.

Addressing the Situation

Addressing the misconceptions found in the student’s defense of natural selection would really depend on the situations. If this is a classroom debate and there are two different sides, the students obviously have some preparation time. As the students are preparing their defense, I would check in with each group and find out how they are using Darwin’s theory of Natural Selection to make a stance.

Classroom debates are a great catalyst to improve comprehension and interest. If I had the opportunity to identify the misconceptions the student’s have before entering the debate, we could develop solid evidence for their defense. As a result, while the students defend their argument, they are using accurate ideas and examples and they learn the correct application of natural selection before the debate.

While meeting with each group individually, I would ask them to pitch their defense to me. I will start with complimenting them with what I liked about their defense, then ask the group:

“Can you explain to me again what ‘survival of the fittest’ means again?”

“So you are telling me that ‘fit’ is a measure of an individual’s strength. Who do you think the strongest person in the world is? (students respond…superman or something). So you would agree that Superman would most likely survive over any other being? (yes). So then what would happen if Superman were unable to have kids? Would he still be most fit in terms of natural selection? Would Superman be naturally selected for in terms of your definition of “survival of the fittest?”

I would discuss this with my students and let them talk it over among themselves while I talk to the other group. I will also first listen while the second group pitches their defense to me. Starting with a compliment, I will then converse with them:

“Explain ‘survival of the fittest to me again.” (students explain)

“OK, so lets think about us humans for a second. Do we all have the same characteristics? (No) Why is that? (gene expression or a response similar – difference in heredity) Are there some characteristics that we some humans have that help us survive in an environment better then those that lack that characteristic? (if no response, hint at skin color). Hypothetically speaking, what would happen if there were a mutation of one person’s genes that gave them the ability to have 9 lives like a cat? What are their chances of survival over yours and mine? (way better) So then if that person how does “survival of the fittest” relate to that one person so that more people like he/she exist? Do you think that would change the gene pool?”

After we discussed this for some time, I will approach the second misconception (although, this might be a stick topic. By addressing the following issue, it might change the group’s main idea completely. Therefore I will have to judge this one. I can always hold off on this explanation until after the debate):

“So your examples state that like honey bees and Captain Lawrence Oates, humans are naturally altruistic and self-sacrificing. Where does this characteristic derive from? (it’s in their genes or they learned from their parents). OK, so if a hive of honey bees were massively attacked, and the bees that possessed the altruistic characteristic died to save their fellow bees, which type of bees are mostly left? (the selfish ones) So if the selfish ones were the predominant bees left, wouldn’t the reproduce more selfish bees? How would they get the altruistic bees back? Or, if the altruistic bees learned this from their parents, is it genetic? Will it be passed on to their children?”

At this point, I would hop between groups to assure they have sound arguments before starting the debate. The point I am trying to make with the first group is that “fit” does not mean strength but rather the chances and/or ability to reproduce. Just because an organism is stronger than another does not always mean those traits will be passed on. Being “fit” means that a certain individual is better adapted to it’s environment and has more chance for reproducing offspring that will also thrive in the same environment.

For the second group, I hope to uncover the real meaning of “survival of the fittest.” Individuals that have a higher probability of survival and reproduction are the “fittest” and their survival contributes to the survival of the species as a whole. The gene pool changes with adaptations and these adaptations occur on an individual level that reflects in the species population over time.