NO. 3655 PARALLEL EVOLUTION—-FRIEDMANN 9 
Here, then, is a series of remarkably parallel situations of similarly 
colored, sympatric species, each with a paler, grayer form in the open 
grasslands of eastern Africa and each with a darker, greener represent- 
ative in the forests of central and western Africa. In some, the repre- 
sentatives are clearly conspecific; in others, they have achieved 
specific distinction—minor and conirostris; meliphilus, willcocksi, and 
exilis; narokensis and pumilio; variegatus and maculatus. 
It is, of course, impossible to state with any certainty either that 
these similar species all originated as greenish forest birds that gave 
rise to paler, grayer races in the open country, or that all began as 
erayish denizens of the savannas and each evolved a darker, greenish 
representative form in the wooded areas. It is equally possible that 
some may have gone one way, and others, the opposite direction; but 
the end result, which is all we have for study, shows a remarkable 
parallelism. As Mayr (1963, p. 609) noted, true parallelism is due to 
the necessarily similar response of a common genetic heritage to similar 
selection pressures. Inasmuch as all of these species of honey-guides 
seem in every way to be closely related, and, hence, to have a basically 
similar genetic composition, their parallel evolutionary picture seems 
to be true parallelism rather than mere convergence, a situation wherein 
similar phenotypic developments have resulted as a response to 
similar environmental selection factors. The small species of Indicator 
have, at best, a very restricted phenotypic potential, much like some 
of the tyrant flycatchers of the genera Empidonaz and Elaenia. 
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