Biological Evolution Explains the Characteristics of Hawaii’s Plants and Animals
Only one known scientific explanation can account for the characteristics and distribution of Hawaii’s flora and fauna. All of the native plants and animals in Hawaii must be descended from organisms that made their way to the initially barren islands through the air or across the water from the surrounding continents and from distant islands. In those cases where the initial colonists survived and produced descendants, the conditions existing in the Hawaiian islands resulted in the evolution of new species with traits found nowhere else in the world.
This process of biological change is described by the theory of evolution. Evolutionary theory holds that all the organisms existing on the earth today are the descendants of organisms that existed on the earth in the past. But today’s organisms are not necessarily the same as past organisms, because living things have the potential to change from one generation to the next. When organisms reproduce sexually, their offspring differ from each other as well as from their parents. For example, an individual insect might have a somewhat different configuration of its wings, a plant might have a thicker stalk, or a mammal might be colored differently. Some of these new traits might be harmful for an organism, causing it to die before it can have its own offspring. But other traits might be advantageous in a particular environment. They might enable an organism to gather food more effectively, live in a place where there is less competition for resources, or avoid predators. If an organism with an advantageous trait can more successfully exploit a particular ecological niche, it has better odds of surviving and is likely to produce more offspring than is an organism without that trait.
Many of the traits of an organism are shaped by interactions between the genetic messages encoded in its DNA and the environment in which it lives. If an individual organism has a trait encoded in its DNA that is advantageous in a given environment, its offspring can inherit that trait through the transmission of DNA between generations. These offspring can in turn pass the trait on to their offspring, so that over many generations the trait gradually becomes more common in a population of organisms. Individual organisms do not evolve during their lifetimes, but over long expanses of time successive generations of organisms can acquire new characteristics that enhance their ability to survive and reproduce.
Consider, for example, a population of drosophilid flies that lay their eggs in the rotting bark of trees in damp forests (see Figure 2). As this population expands and moves into new areas, it may encounter forests in drier regions. There some flies may attempt to lay their eggs in trees where running sap has dampened the bark. Those flies that are most able to lay their eggs in this new substrate, whether because of their behavior or the shape of their bodies, would likely produce more offspring, and these offspring will tend to inherit their parents’ traits. Over time, a population of flies will develop with traits more suited to laying eggs in sap-dampened bark than in rotting bark. Indeed, just such a transition occurred several times during the evolution of the Hawaiian drosophilids.
The evolution of a new trait can have important consequences. Within a population of flies adapted to laying its eggs in sap-dampened bark, other variations in behavior or morphology