How organisms, move, obtain food, reproduce and respond to danger, all are based on the organism s evolutionary history. Content Standard Life Science 5-8 NSES Content Topic Diversity and Adaptations of Organisms Biological evolution accounts for a diversity of species developed through gradual processes over many generations. Species acquire many of their unique characteristics through biological adaptation, which involves the selection of naturally occurring variations in populations. Biological adaptations include changes in structures, behaviors, or physiology that enhance reproductive success in a particular environment. Extinction of a species occurs when the environment changes and the adaptive characteristics of a species do not enable it survive in competition with its neighbors.
Fossils indicate that many organisms that lived long ago are now extinct.
Extinction of a species is common. Most of the species that have lived on Earth no longer exist. The great diversity of organisms is the result of more than 3.5 billion years of natural selection and evolution that has filled every available niche with life forms. Natural selection and its evolutionary consequences provide a scientific explanation for the fossil record of ancient life forms, as well as for the striking molecular similarities observed among the diverse species of living organisms. The millions of different species of plants, animals, and micro-organisms that live on Earth today are related by descent from common ancestors.