co-evolution

Co-Evolution

In biology, coevolution occurs when two or more species reciprocally ("co-") affect each other's evolution. Charles Darwin mentioned evolutionary interactions between flowering plants and insects in On the Origin of Species (1859). The term coevolution was coined by Paul R. Ehrlich and Peter H. Raven in 1964.

One of the most important parts of an organism's environment is other organisms. Co-evolution occurs when, in adapting to their environments, two or more organisms evolve together. To "make the best of" where they live, organisms make use of other organisms by eating them, living on or in them, and/or building a "partnership" with them. Organisms co-evolve with many species at the same time, because an environment includes many different types of organisms.

Organisms have to adapt to form these relationships just as they have to adapt to any other part of their environments. These adaptations cause so much change that descendants, who are better suited to take advantage of the relationship, are so different that they may be an entirely different species from their ancestors.

It is important to note that species that are closely related did not always appear at the same time. For example, although the first mammals appeared approximately 225 million to 180 million years ago, not all mammal species appeared at that time. This is especially important to realize in the case of co-evolution. Organisms have co-evolved whose families first appeared very far apart on evolution's time scale. For example, the first segmented flatworms originated millions of years before the first mammals. However, the tapeworm, a segmented flatworm that is a parasite of humans, cows, and other mammals, could not have evolved before the first large mammals, because it adapted so much to the parasitic relationship that its ancestors before the relationship were not of the same species of worm.

Defense Mechanisms
Coevolution is manifested in defense mechanisms as well as attractants: Botanical structures and chemicals (secondary metabolites) have evolved to discourage or to prevent the attention of plant eaters.

These include the development of spines, barbs, thorns, bristles, and hooks on plant leaves, stems, and trunk surfaces. Cacti, hollies, and rose bushes illustrate this form of plant strategy. Some plants produce chemical compounds that are bitter to the taste or poisonous.

Plants that contain organic tannins, such as trees and shrubs, can partially inactivate animals’ digestive juices and create cumulative toxic effects that have been correlated with cancer. Grasses with a high silica content act to wear down the teeth of plant eaters.

Animals have counter adapted to these defensive innovations by evolving a higher degree of resistance to plant toxins or by developing more efficient and tougher teeth with features such as harder enamel surfaces or the capacity of grinding with batteries of teeth.