Reference no: EM132934696

A biologist studies the grass plants in two fields. Both fields are fenced to keep all-natural grazing wildlife (such as deer) out. Both are exactly the same size and are located in the same county, at the same elevation. Extensive measurements show that both fields have exactly the same simultaneous amount of rain, snow, and sunshine, and that the simultaneous temperatures are also the same for both. Before beginning an experiment, the biologist randomly collects representative grass seed from each field, plants the seed under identical controlled conditions, and allows the resulting grass to grow to maturity. The heigh of each resulting grass plant is measured and the average heights of the grass plants grown from seed in each field are shown to statistically identical.

The biologist then introduces goats to graze on one of the fields, while the other has no grazing animals present. A the end of a 5-year period, the biologist again randomly collects representative grass seed from each field, grows the seed under identical controlled conditions, and allows the resulting grass to grow to maturity. The height of each resulting grass plant is measured and the average height of the grass plants grown from seed collected in the field where grazing occurred was shown with statistical significance to be 4 cm shorter than that of the fields where no grazing occurred.

What is the Darwinian principle that can explain this difference in average height between the grass from each field? What are the independent and dependent variables in the experiment? What was the control?