If the rate of speciation or variation in a clade is greater than the rate of extinction, the clade is likely to survive. On the other hand, if the rate of extinction is greater than the variation within the clade, the clade would face extinction.

The two models that are used to describe the rate of evolution includes gradualism and punctuated equilibrium. When a geologic change occurs in a slow and steady rate rather an abrupt one, the evolution happens over a long period of time. This pattern of evolution is said to be under the gradualism theory. On the contrary, a punctuated equilibrium occurs when a period of stability is ceased by brief periods of rapid changes.

In adaptive radiation, single species evolve into different groups in order to fill new or different ecological niches. This pattern of evolution happens in related species. On the contrary, in convergent evolution, organisms that are not closely related forms similar structures that are favored by natural selection. Eventually, different organisms become more alike due to this pattern of evolution.

Coevolution is responsible for the evolutionary change that happens between two or more species that are closely related to one another, particularly in organisms that have competitive associations like predator-prey and host-parasite relationships. It is characterized by the evolutionary change in one organism that is often followed by a change in another organism.

For example, the polar bear’s fur has evolved over time from a brown color into a white color in order to blend in the snowy environment. In this way, its prey, which is the seal, would not notice when it is approaching. On the other hand, the seal’s offspring has evolved into a white color to avoid being eaten by the bear.

The reason for this is because the major geologic changes, such as abnormal climate conditions, movement of plates, volcanic eruptions, changing sea levels, and collision of comets and asteroids, often cause harm or damage in the habitat of organisms. This leads to the destruction of the entire ecosystem. Since it can no longer sustain life, mass extinction occurs.

Sheep, goats, antelopes, and deer are all members of the Order Artiodactyla, which is also known as even-toed ungulates. However, the deer branched off and evolved separately from sheep, goats, and antelopes. Deers are members of the family Cervidae, whereas sheep, goats, and antelopes are from family Bovidae.

Therefore, these animals did not evolve from a common ancestor that has horns. Instead, they all evolved from a hoofed mammal. Moreover, the deer evolved from a cervid that has antlers, whereas sheep, goats, and antelopes evolved from a bovid that has horns.

Aquatic animals experienced changes in their morphological structures and developed adaptations that are suited for terrestrial life. These vertebrates acquired lungs for respiration, neck for mobility, and limbs that can support their weight during walking when they moved to the land. Moreover, some scientists believe that natural selection is the driving force of this evolutionary pattern. The changes in the water condition, such as temperature and salinity, have forced some of the organisms to move to the land and the shallower parts of the water.