Unit 6: The Changing Nature of Life

Unit 6: The Changing Nature of Life

Adaptation is based on the concept that organisms' populations change over time due to natural selection. Adaptive evolution is driven by increased survivorship and increased reproductive success. This happens when a collection of individuals in a population gain an advantage because of their unique traits. These traits may be either inconspicuous or quite elaborate. For example, they may start 2 mm lengthening in the nectar-gathering tongue of a few moths that feed on orchids. If beneficial, the tongue may become much longer in that species over time as those individuals and their offspring out-reproduce others. Eventually, the long shape becomes the norm because the long-tongued adaptation, which allows more efficient feeding, contributes to increased reproductive success.

Darwin discovered an orchid with a vast, 11-inch-long nectar-producing tube in Madagascar. He predicted that there would be a moth that feeds from the tube with an 11-inch proboscis. Almost 50 years later, Darwin's prediction proved true when scientists discovered the moth Xanthopan morganii praedicta with a 12-inch proboscis that fed and pollinated Darwin's orchid (Angraecum sesquipedale). Of course, the ultimate source of an adaptation like this, and all others, is genetic because only traits that can be passed on from one generation to the next are influenced by natural selection.

Darwin's orchid-and-moth example is one of the more visible cases of adaptation. One feature of a plant is associated with a corresponding feature of an animal so that both benefit from their interconnected lives in nature. But more generally, organisms are a mass of adaptations that combine to make a particular lifestyle work. Why? Because many factors in the environment are 'problems' that require 'solutions.' The availability of food, predator-prey relationships, and climate all play an essential role in selecting 'through natural selection' beneficial characteristics.