Each living thing is adapted to its mode of life in a general way, but each is adapted especially to its own distinct niche. A plant, for example, depends upon its roots to anchor itself and to absorb water and inorganic chemicals. It depends upon its green leaves for photosynthesis, the process of using the sun's energy to manufacture food from inorganic chemicals. These are general adaptations, common to most plants. In addition, there are special adaptations that only certain species of plants possess. The mistletoe, for example, is a parasitic plant; it lacks true roots but lives with its rootlike haustoria buried in the branches of a tree. It depends upon the tree to anchor itself and to absorb water and inorganic chemicals. In order to survive, the mistletoe must establish its parasitic relationship with a suitable tree. The mistletoe is also dependent upon an insect to pollinate its flowers, and a bird to disseminate its seeds by eating the berries and depositing its droppings containing the seeds onto the branches of appropriate trees.

Many animals have adaptations that help them elude their predators. Some insects are camouflaged by their body color or shape, and many resemble a leaf or a twig. The coats of deer are colored to blend with the surroundings. Their behavior, too, is adaptive: they have the ability to remain absolutely still when an enemy is near. These adaptations arose from the natural selection of heritable variations.

Organisms have a great variety of ways of adapting. They may adapt in their structure, function, and genetics; in their locomotion or dispersal for defense and attack; in their reproduction and development; and in other respects. Favorable adaptations may involve migration for survival under certain conditions of temperature, for example. An organism may create its own environment, as do warm-blooded mammals, which have the ability to adjust body heat precisely to maintain their ideal temperature despite changing weather. Adaptations to temporary situations may be reversible, as when humans become suntanned.

Usually adaptations are an advantage, but sometimes an organism is so well adapted to a particular environment that, if conditions change, it finds it difficult or impossible to readapt to the new conditions. The huia bird of New Zealand, for example, depended upon a close collaboration between male and female: the male chiseled holes in decaying wood with its stout beak, and the female reached in with her long, slender beak to capture grubs. When New Zealand was deforested, these birds could no longer feed in their accustomed way and soon became extinct. (See also Evolution.)