How Green Beetles Took Over: Natural Selection

Hi, I'm Atlas. Let's solve a real mystery in this meadow. Look closely: the beetles are not all the same. Some are brown and some are green. These small differences are called variation. Because the differences come from a beetle's parents, we say the variation is heritable — meaning parents pass traits to their offspring. Now add the birds. Birds love eating beetles, but on these green leaves the brown beetles are easy to spot, while green beetles blend in and hide. So more green beetles survive long enough to have babies. Surviving and reproducing more than others is called differential survival and reproduction. Here is the key idea: the green beetles do not turn green on purpose. They were already green when they hatched. They simply survived more often, so they had more green offspring. After many generations, most of the population is green. That slow change in a whole population over time is natural selection. It explains adaptation — how traits in a population become better suited to the environment over generations. (Natural selection is just one piece of the larger story of biodiversity; we will explore that in later lessons.) If this feels tricky, slow down and remember the recipe: heritable variation, then survival of some, then more offspring with the same trait. Then try the sorting activity below.