For the littlest ones, evolution is a matter of self-selection. Microbes carve their own evolutionary path by managing their own genetics. Viruses, archaea, and bacteria frequently decide how to adapt themselves to environmental conditions via self-generated genetic modifications. One way they do so is by sharing genetic concepts among themselves: a process called horizontal gene transfer. These ready-made adaptations, which microbes selectively employ, can facilitate the rapid evolution of populations. Thus, resistance quickly arises in populations of pathogens subjected to antibiotics.
At the organism level, adaptation visibly appears via bodily change. Physiological changes are often the tip of the iceberg to functional transformations, including behaviors.
The threat of being killed for food has long been recognized as a key ecological factor for adaptive responses. Predation risk also drives the evolution of social complexity. Groups become more cohesive under the threat of becoming dietary casualties. Organisms stay together to maximize their statistical chances of staying alive.
Sociality is not without costs, but these are far outweighed by the benefits. Hence, sociability is the norm for organisms throughout the tree of life.
Worldwide, coral reefs are presently under severe stress from ocean warming and acidification. Only to a limited degree can coral quickly adapt on their own. To better acclimatize, coral hire algal symbionts that can stand the heat. The coral gets improved temperature tolerance, and the algae find themselves safely harbored in a well-furnished home.
Evolutionary fitness is strengthened by cooperation. Life is not a hierarchy. It is an entangled web.