Answers to exploration questions: the evolutionary causes of biodiversity

If you are wondering where the suggested answers came from, you can review the videos and articles in this tutorial.

1.     In this tutorial, the narrator says that Darwin’s description of natural selection as “survival of the fittest” should actually be “survival of the fitter”. In your own words, explain why survival of the fitter is a more accurate description of how natural selection works on individual members of a population or species. Hint: review the video example of redwood tree adaptations if you need some ideas about how to explain this concept.

Answer: A complete explanation would start by mentioning that natural selection works on the variation that exists among individuals of the same species. For instance, individuals can show variation in their behavior that might determine how well they attract a mate, or in their physiology that might determine how well they are able to survive a disease, or in a physical trait such as tree trunk height that determines how much food the leaves can make from sunlight. All of this variation determines an individual’s overall fitness, or how likely they are to survive and reproduce. Another way of saying this is how well adapted they are to their environment. The phrase “survival of the fittest” implies that there is a single, best end point to fitness in a population. But there isn’t! An individual doesn’t have to be the most fit ever; it just has to be a little bit better or more fit than other individuals in the population to reproduce more and pass on more of its unique combination of genetic information. How fit or well adapted an individual is all depends on the particular environmental conditions or constraints under which it is living. And as we know, environmental conditions change with time and human influence.

2.     Your friend tells you that biodiversity is increased when a species decides to evolve into a new species. Do you agree or disagree with your friend’s explanation of how speciation occurs? Hint: Review the video example of the formation of the Isthmus of Panama.

Answer: A complete explanation would mention that although speciation does indeed increase biodiversity, speciation does not occur because a species decides to become a new species. There is no conscious control or decision-making involved. Species do not possess the ability to decide to evolve into a new species. The environmental conditions impose a selection pressure on the individual members of a population or species. Those individuals well adapted to the current conditions survive better and reproduce more. And they breed with each other across the whole population, maintaining gene flow and the traits of that single species. But if something happens in the environment to restrict the gene flow, to subdivide the single population into separate, isolated populations that do not interbreed, the stage is set for speciation to occur. When sea levels changed and the Isthmus of Panama appeared, it separated or isolated porkfish on each side of the land bridge, and over time the Atlantic and Pacific populations each evolved into new species.

3.     Consider the following fictional scenario: A population of lions is living in the wilds of sub-Saharan Africa. A genetic mutation occurs that causes the lion’s roar to be silent. This mutation is heritable and can be passed down to future generations in the population. Describe one scenario in which this mutation would be selected for and would increase in future generations, and describe another scenario in which it would be selected against. For both scenarios, be sure to explain why the silent roar mutation would be selected for or against.

Answer: There is no specific right answer here; this is a question for your creativity. In both scenarios you have to consider what environmental conditions might make a silent roar advantageous or disadvantageous. For example, a silent roar might be advantageous if humans establish a settlement near the lions’ habitat and whenever they hear lions roaring they go out and shoot the roaring lion. Or perhaps a lion that roars silently doesn’t attract as many competitor lions trying to steal their mate or food. Selection for the silent roaring trait means that lions that roar silently will survive better and reproduce more, passing on the genetic information for silent roaring; and over time, over many generations, the frequency of silently-roaring lions will increase in the population. On the other hand, there might be selection against silent roaring if, for example, lions that don’t make any sound when they roar can’t find a mate or get separated from their group and don’t have any help catching prey. In this case, silent roaring would be disadvantageous and you would expect the trait to be selected against. The trait would decease in frequency in the population over time or maybe even be eliminated completely.