Question of The Day

According to the passage, adaptive convergence and adaptive divergence are

The opposite of adaptive divergence is an interesting and fairly common expression of evo- lution. Whereas related groups of organisms take on widely different characters in becoming adapt-  (5) ed to unlike environments in the case of adaptive divergence, we find that unrelated groups of organisms exhibit adaptive convergence when they adopt similar modes of life or become suited for special sorts of environments. For example, (10) invertebrate marine animals living firmly attached to the sea bottom or to some foreign object tend to develop a subcylindrical or conical form. This is illustrated by coral individuals, by many sponges, and even by the diminutive tubes of bry-­ (15) ozoans. Adaptive convergence in taking this coral-like form is shown by some brachiopods and pelecypods that grew in fixed position. More readily appreciated is the streamlined fitness of most fishes for moving swiftly through water; (20) they have no neck, the contour of the body is smoothly curved so as to give minimum resis- tance, and the chief propelling organ is a power­ -ful tail fin. The fact that some fossil reptiles (ichthyosaurs) and modern .Mammals (whales, (25) dolphins) are wholly fishlike in form is an expres -sion of adaptive convergence, for these air-breath­ -ing reptiles and mammals, which are highly effi- cient swimmers, are not closely related to fishes. “Unrelated or distantly related” organisms that (30) develop similarity of form are sometimes desig­ -nated as homeomorphs (having the same form).

compensatory adjustments made in response to unlike environments