Misconception: “Evolution means that life changed ‘by chance.’ ”

Response: Chance is certainly a factor in evolution, but there are also non-random evolutionary mechanisms. Random mutation is the ultimate source of genetic variation, however natural selection, the process by which some variants survive and others do not, is not random.

For example, some aquatic animals are more likely to survive and reproduce if they can move quickly through water. Speed helps them to capture prey and escape danger. Animals such as sharks, tuna, dolphins and ichthyosaurs have evolved streamlined body shapes that allow them to swim fast. As they evolved, individuals with more streamlined bodies were more likely to survive and reproduce. Individuals that survive and reproduce better in their environment will have more offspring (displaying the same traits) in the next generation. That's non-random selection. To say that evolution happens “by chance” ignores half of the picture.

The streamlined shape of these yellowfin tuna is no accident. A more streamlined shape allows these fish to move through the water faster. During their evolution, natural selection favored the more streamlined tuna.


• Tuna photo courtesy of the NOAA/Dept. of Commerce.

"Trying" to Adapt

Search · Site Index · Navigation · Copyright · Credits · Contact
Understanding Evolution For Teachers Home · Understanding Evolution Home

Read how others have recognized the Understanding Evolution website

Spanish translation of Understanding Evolution For Teachers from the Spanish Society of Evolutionary Biology.