intergrade

[ noun in-ter-greyd; verb in-ter-greyd ]

/ noun ˈɪn tərˌgreɪd; verb ˌɪn tərˈgreɪd /

an intermediate grade, form, stage, etc.

to merge gradually, one into another, as different species through evolution.

Origin of intergrade

First recorded in 1870–75; inter- + grade

The two subspecies of the Violet-green Swallow, thalassina and lepida, intergrade in Coahuila.

Birds from Coahuila, Mexico |Emil K. Urban
The subspecies cahooni and compositus of the Brown-throated Wren seem to intergrade in the southern part of the State.

Birds from Coahuila, Mexico |Emil K. Urban
Previously the two kinds were thought not to intergrade and were regarded as two species.

Speciation of the Wandering Shrew |James S. Findley
The specimen from Chanquejelve is an intergrade between the two subspecies just mentioned.

New Subspecies of the Rodent Baiomys From Central America |Robert L. Packard

For the present it seems best to regard the specimen merely as an intergrade.

American Weasels |E. Raymond Hall

intergrade

(intr) (esp of biological species, etc) to merge one into another

an intermediate stage or form

intergradation, noun intergradational, adjective intergradient, adjective