9 B. Natural Selection Because evolution occurs over a long time period it is difficult to look at in nature. However, many of the selection pressures are measurable and we can see the process of natural selection at work if we look at a few subsequent populations. We know that mutations occur at random in populations and that they contribute to changes in the genetic make-up of the population. If a mutation is advantageous, it will likely become more prevalent within the population over time. Looking at some observations of nature and then making inferences from those observations can help us logically break down Darwin’s theory of natural selection. Facts Based on Observations of Nature: •Organisms express variations, some of which are inheritable. •More individuals are born than survive to reproduce. •Competition for resources occurs between individuals. Inferences from Observations: •
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