BIO 118 .docx - Oriya Romano Bio 118 Intro to Cell and...

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Oriya Romano Bio 118- Intro to Cell and Molecular Biology Fall 2017 Why do giraffes have long necks? Science is a process of asking a question, testing a hypothesis (A testable explanation often based on some type of observation, explanation, evidence Hypothesis can be tested by an observation or experimental process) Example: Giraffes have long necks to reach food unavailable to other mammals. An alternate hypothesis was proposed by Roberts Simmons and Lue Scheepers: Giraffes have long necks to use as effective weapons against their opponents. In order to test these hypothesis scientists must: Design an observational or experimental study that tests the predictions. A hypothesis can either be rejected due to the evidence, a demonstration that the prediction is inaccurate, OR A hypothesis can fail to be rejected (ie. supported) by the evidence…. A hypothesis is never proven (the best a hypothesis can ever be is the best possible explanation). If it fails to be rejected many many times, it becomes a theory . Food competition hypothesis: 1. Giraffes compete with other mammals for food, and giraffes with longer necks can reach food that other animals cannot reach. (long neck is a heritable trait) Thus, giraffes with longer necks would survive better and produce more offspring with longer necks, shifting the giraffe population over time to have long necks. (ones with shorter necks would die out due to lack of food) 2. Giraffes feed high in trees, especially during the dry season when food is scarce and the threat of starvation is high. This is an observational study done to prove the food competition theory These graphs showed that the hypothesis is rejected They aren’t feeding at their average height and most of the time giraffes even have their necks bent when they feed This was done in both wet and dry seasons Sexual competition hypothesis: Males fight amongst themselves for the opportunity to mate. Giraffes with longer necks strike harder blows, and have more opportunities to mate. Thus, giraffes with longer necks would produce more offspring with longer necks, shifting the giraffe population over time to have long necks. Since again, it is a heritable trait. Male giraffes with longer Chapter 1- Intro
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necks are more successful at fighting and gain more access to females. Several studies have shown that these predictions are accurate. Thus, providing evidence that fails to reject the sexual competition hypothesis Sexual competition is certainly playing an important role in the evolution of this trait but other pressures may be contributing as well…including food competition.
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