Which graph represents selection that may lead to reduced variation in a population?

A frequency graph can represent selection to illustrate population variation. 

Frequency graphs are used to represent data to identify a range of measure. It displays a visual illustration that presents frequency counts to make the information be interpreted more easily. It also shows an absolute distribution or relative frequencies like precentages or proportions. Frequency table or Frequency graph is the simplest method to show the number of occurrences of a particular characteristics. Histograms or bar charts are both displays of frequencies. This is done through plotting columns on a graph. It is usually written thru an X and Y axis which generally represents a measured variable and frequency count, respectively.