A biologist wants to know whether a plant's growth is affected by the material it's planted in. She plants lima bean seeds in a jar of dirt, a jar of cotton, and a jar of rocks, then provides each jar with equal amounts of water, plant food, and sunlight. In this experiment, the independent variable is the material in which the plant is getting planted.
The independent variables are the variable that are in control of the experimenter. The independent variables do not depend on the other variable for their selection. The changes in a dependent variable is studied by varying the independent variable accordingly.
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<span>A certain virus infects one in every 200 people. A test used to detect the virus in a person is positive 90% of the time if the person has the virus and 5% of the time if the person does not have the virus. (This 5% result is called a false positive.) Let A be the event "the person is infected" and B be the event "the person tests positive".
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The relative shortness of time they have been separated is the most important for explaining why there are equal numbers of snapping shrimp species on either side of the isthmus.
Speciation is the process of forming new species.
There are five main types of speciation:
- Allopatric speciation
- Sympatric speciation
- Peripatric speciation
- Parapatric speciation
- Artificial speciation
Although allopatric speciation is the most common type of speciation, all five types are described in more detail in the following sections.
Allopatric speciation occurs when one population is physically separated by a geographic barrier and slowly evolves into two separate species. With separation into different environments comes different environmental pressures that shape natural selection, the survival of the most fit organisms in the environment. These different environments allow for different traits to be selected.
Over time, the selection can create entirely new species. For example, snapping shrimp are a group of shrimp that were separated by the Isthmus of Panama across the Caribbean Sea. Over time, the selective pressures were so different that the populations of shrimp evolved into different species.
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