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What is Natural Selection?


To many people, natural selection is a confusing and even controversial topic in biology. In reality, natural selection is very logical and easy to understand.


We’ll start with an example: A population of moths that spend their days hiding on trees with white bark. Most of the moths are pale in color, but they range all the way from dark gray to white. Moths that match the color of the tree bark most closely are hardest for birds to find and eat.


Let’s say a factory moves next door to the forest where the moths live. The factory releases a lot of soot, which settles on the tree bark and turns it a dark gray color. Now the pale-colored moths are easier for the birds to see, while the darker moths have better camouflage.


Since more of the pale-colored moths are eaten before they can reproduce, fewer pale-colored genes get passed on to the next generation. Even though there used to be far more pale-colored moths in the population, over time the population will become darker as more dark-colored genes get passed on. This is an example of natural selection


















A naturalist named Charles Darwin first developed the idea of natural selection after his voyage through the Galapagos Islands. Darwin noticed that the finches he saw on different islands were almost identical to the birds he saw on the mainland, except for their beaks; finches on different islands had different sizes and shapes of beaks to best make use of whatever food source was found on that particular island.


Darwin realized that these new finch species must have originated when finches flew over from the mainland, and then eventually changed into distinct species since only the birds adapted for that island’s food source survived to pass on their genes.


Darwin’s Theory of Natural Selection is based on four main points. First, individuals of a species have a variety of different traits. Second, traits are passed down from generation to generation. Third, more offspring are produced than will survive to adulthood. Fourth, only the animals best adapted to survive the competition for resources will pass on their genes.


We can actually observe natural selection even over the short term. If you were to put a bunch of bacteria on an agar plate treated with antibiotics, most of the bacteria would die. However, a few bacteria would have genes that made them resistant to the antibiotic, and within a very short period of time the bacteria population would be made up entirely of antibiotic-resistant bacteria. This is why doctors don’t use antibiotics if it’s not strictly needed, because using them too often will naturally select for bacteria that are resistant to antibiotics.