Descent with Modification
Darwin’s theory of descent with modification proposed that all species must have descended from original, preexisting species and that they must be able to undergo change over time. Descent with modification is evident with Struthioniformes and the five different species of kiwis found across the country of New Zealand and the surrounding islands. The species of kiwis are geographically isolated from one another and living in different climate areas. Each species differentiated themselves from one another by adapting to their own individual environment and passing on favorable traits, such as feather color and pattern, to their offspring. For instance, the great spotted kiwi has a plumage of feathers in a stripe-like pattern that ranges from charcoal gray to light brown. Another species, the north island brown kiwi, has a streaky red-brown and spiky plumage. These different types of plumage allows the kiwis to better camouflage in their own environment. Even though the kiwi species are different, they can all be traced back with the other struthioniformes to a common ancestor.
Natural Selection
Darwin’s theory of natural selection states that organisms that are better adapted to their environment tends to survive and reproduce in greater numbers than others of their kind, thus ensuring that those favorable traits are passed down to the
next generations. This concept is a key mechanism of evolution and is what causes the change of inherited traits over time. Based on the trait of leg strength, struthioniformes underwent directional selection. Ostriches have long, powerful legs that allows them to run great distances at even greater speeds. Emus legs are strong, thick, able to trot for long distances, and capable of jumping up to seven feet straight up. Kiwis have small, but muscular legs that makes up a third of the bird’s total body weight. They are used to silently run and fight. Having muscular legs is an advantage for struthioniformes because it compensates for their lack of ability to fly. They travel and migrate long distances on land with their legs rather than by wings, and they defends themselves from predators with their strong kicks instead of flying away.
Order Struthioniformes 