UC Berkeley
Image Caption
Through sampling error, genetic drift can cause populations to lose genetic variation. Imagine that our random draws from the marble bag produced the following pattern: 5:5, 6:4, 7:3, 4:6, 8:2, 10:0, 10:0, 10:0, 10:0, 10:0… Why did we keep drawing 10:0? Because if the green marbles fail to be represented in just one draw, we can't get them back — we are "stuck" with only brown marbles. The cartoon below illustrates this process, beginning with the fourth draw.
Image use policy: For non-commercial, educational purposes, this image may be used with a Creative Commons CC BY-NC-SA 4.0 license. Please credit as follows: © University of California Museum of Paleontology, Understanding Evolution, www.understandingevolution.org
See where this image appears on the Understanding Evolution website »
To save: 1) Click on image for the full-size version, 2) right-click (Windows) or control-click (Mac) on the image, and 3) select "Save image."