In evolutionary biology, convergent evolution is the process by which two organisms or taxonomic groups have a character in common due to independently adapting to a similar environment or niche, not by homology.
An example of this would be the similarities in behavior and morphology between bats and birds. Although superficially very similar, the two groups are considered by evolutionists to be only very distantly related (being grouped only within the clade Reptilia). Their similarities are therefore considered to be a result of evolution in response to nearly identical ecological niches and pressures.
Convergent evolution is a theory and has not been observed in action. Also, it presents the following conceptual problems. First, it requires that random chance produce the same outcome in at least two independently occurring instances, which is substantially less likely even than doing so once. Such evolutionary coincidence is a less plausble explanation than one that evolutionists assume away, namely, a common Designer. Second, because convergent evolution would work by random chance rather than by being intelligently guided, simple probability indicates that even if it produced a good result in a particular structure (e.g., an eye) in one organism, it might well produce a suboptimal result in that same structure in another organism. No such result has been observed.