EVOLUTION IN HAWAII
A SUPPLEMENT TO TEACHING ABOUT EVOLUTION AND THE NATURE OF SCIENCE
Hawaii Is One of the Best Places in the World to Study Biological Evolution
The biodiversity of the native plants and animals that live in the Hawaiian islands is breath-taking. On the northern and eastern sides of the islands, where the trade winds drop their moisture on upsloping hills and mountainsides, luxuriant rainforests contain a profusion of species of trees, shrubs, birds, and insects. On the southern and western sides of the islands—often just a few miles away—open landscapes of grasses and shrubs receive just a few inches of rain a year. On the flanks of the high volcanoes of Maui and the Big Island of Hawaii, scattered bushes and hardy flowering plants endure frequent frosts and even an occasional snowfall. In the reefs surrounding the islands, hundreds of species of tropical fish swim amid colorful beds of coral.
Where did all these plant and animal species come from? The Hawaiian islands consist of the tops of mid-ocean volcanoes, are about 4,000 kilometers (2,500 miles) from the nearest continent, and have never been connected to any body of land (see Figure 1). Plants and animals therefore could not have taken an overland route from continents such as Asia or the Americas to reach the islands. Many of the plants and animals on the islands are so similar to species elsewhere that they obviously were brought to Hawaii by the humans who began colonizing the islands between approximately 1,200 and 1,600 years ago. But many other plant and animal species on Hawaii are so different from organisms elsewhere that they must be native—that is, they had to be present on the islands before the arrival of human beings.
The characteristics of native Hawaiian plants and animals raise further questions. Most native Hawaiian species are endemic, which means that they are found in Hawaii and nowhere else in the world. How did these unique species come to live only in the Hawaiian islands?
Furthermore, though the islands have a rich variety of flowering plants, insects, birds, land snails, and fish, they have no native species of reptiles, amphibians, or conifers, and a single species of bat and a seal species are their only living native mammals. Why do some kinds of organisms live in Hawaii but not others?
Finally, some categories of native Hawaiian plants and animals are represented with remarkable abundance. For example, approximately 800 species of flies belonging to the genera Drosophila and Scaptomyza exist in the Hawaiian islands—about a quarter of the worldwide total and far more than are found in a comparable area anywhere else on earth. But only about 15 percent of the world’s total of insect families is represented in Hawaii. Before the arrival of humans, Hawaii had no native species of termites, ants, or mosquitoes, according to the fossil record.How can all these facts be explained?